1,2‐Silyl migration in 1‐halonaphthalenes catalyzed by I₂

Abstract

1‐Halo‐8‐hydrosilylnaphthalenes undergo 1,2‐silyl migration to form 1‐halo‐7‐silylnaphthalenes. The influence of the substituents on the silicon atom, the solvent effect, and the D‐labeling experiments are investigated. The migration process may include four steps: (a) generation of acid (HI) by the reaction of the hydrosilane with I₂, (b) protonation of the naphthalene ring, (c) silyl group migration in the protonated intermediate, and (d) deprotonation of the naphthalene ring.

1 INTRODUCTION

Silyl migrations have received much attention in terms of mechanistic considerations as well as synthetic utilities because the migratory aptitudes of silyl groups are higher than those of organyl groups.1 Silyl migrations can be classified as neutral, cationic, anionic, and radical migrations. Although anionic migrations have been well studied, cationic migrations have been less thoroughly explored. As a typical example of the cationic migration, 1,2‐bis(trimethylsilyl)benzene I underwent 1,2‐rearrangement to its 1,3‐disilyl isomer II in an acid‐catalyzed manner (Scheme 1).2 1,8‐bis(trimethylsilyl)naphthalene III similarly afforded 1,7‐disilyl isomer IV. 1‐Silylnaphthalene V also underwent 1,2‐rearrangement to its 2‐silyl isomer VI (Scheme 1).3 The main driving force for these migrations was discussed to be relief of steric compression.

Scheme 1

Silyl migration in 1,2‐disilylbenzene I, 1,8‐disilylnaphthalene III, and 1‐silylnaphthalene V

Here we report cationic 1,2‐silyl migration in 1‐halo‐8‐(hydrosilyl)naphthalenes 1 and 2, during which a hydrosilyl group at the eight‐position undergoes migration to the seven‐position to form 3 and 4, respectively, upon standing, on silica gel, or in the presence of catalytic amounts of I₂ (Scheme 2).

Scheme 2

1,2‐Silyl migration in 1‐halo‐8‐silylnaphthalenes 1 and 2

2 RESULTS AND DISCUSSION

2.1 Preparation of 1‐halo‐8‐silylnaphthalenes

1‐Halo‐8‐silylnaphthalenes 1, 2, 5, and 6 were prepared in good yields by lithium‐halogen exchange of 1,8‐dihalonaphthalenes 7 with n‐BuLi and the subsequent treatment with chlorosilanes (XR₂SiCl) (Scheme 3).4-6 Methoxysilane 5a was also obtained by chlorination of 1a with trichloroisocyanuric acid (TCCA) and alcoholysis of 8 (Scheme 4).7, 8 Reduction of 5a with LiAlD₄ afforded deuterated silane 1a‐D (Scheme 5).9 The structures were characterized by NMR spectroscopy.

Scheme 3

Preparation of 1‐halo‐8‐silylnaphthalenes 1, 2, 5, and 6

Scheme 4

Preparation of 1‐halo‐8‐(methoxy)silylnaphthalene 5a

Scheme 5

Preparation of 1‐halo‐8‐deuteriosilylnaphthalene 1a‐D

2.2 Silyl migration in 1‐halo‐8‐silylnaphthalenes

Upon standing in air for 3 days, 1‐iodo‐8‐silylnaphthalene 1b underwent 1,2‐silyl migration to afford 1‐iodo‐7‐silylnaphthalene 3b.11 The migration was observed even under nitrogen atmosphere, but it was slow (ca. 3 months).
No other product was observed in the ¹H NMR spectra as shown in Figure 1. The silyl migration also occurred when 1b was subjected to column chromatography on silica gel eluted with hexane. The ¹H resonance of the proton bonded to the silicon atom was shifted upfield from δ = 5.66 ppm in 1b to δ = 4.59 ppm in 3b.

Figure 1

¹H NMR spectra of 1‐iodo‐8‐silylnaphthalene 1b and 1‐iodo‐7‐silylnaphthalene 3b

The silyl migration was promoted by a catalytic amount of I₂ (Scheme 6). The silyl migration in 1‐halo‐8‐silylnaphthalenes 1, 2, and 6 was monitored by ¹H NMR spectroscopy. A solution of the substrate in CDCl₃ or C₆D₆ was treated with I₂ (5 mol%) in an NMR tube for 5 minutes or less, and the reaction mixture was directly subjected to ¹H NMR spectroscopy. The yields of the products were estimated by using cyclohexane as an internal standard.

Scheme 6

1,2‐Silyl migration in 1‐halo‐8‐silylnaphthalenes 1, 2, and 6 catalyzed by I₂

The results of these experiments are summarized in Table 1. Dimethylsilyl derivatives 1 produced the migrated products 3 in 33%‐81% yields in addition to protodesilylated products 9 in 19%‐64% yields. Diphenylsilyl derivatives 2 afforded migrated products 4 in 10%‐21% yields with protodesilylated products 9 (34%‐56% yields) and 2 (30%‐45% yields). The amount of I₂ was also significant, as only protodesilylated products 9 were obtained from 1, 2, and 6 in the presence of 50 mol% I₂. The migrated products were obtained in higher yields in hexane and C₆D₆ than in CDCl₃. Dimethylsilyl derivatives 1 produced the migrated products in higher yields than diphenylsilyl derivatives 2.

The migration reactions of 1 and 2 were also performed in a reaction flask in hexane or hexane‐toluene, and migrated products 3 and 4 were isolated in 38%‐83% yields, as summarized in Table 2.

Table 1. 1,2‐Silyl migration reactions in an NMR tube

	R	X	Y	Solvent	Time (min)	Products (yield (%))a^a The yields were estimated in the ^1H NMR spectra using cyclohexane as internal standard.
1a	Me	H	Br	CDCl3	1	1a (0)	3a (33)	9a (64)
1a	Me	H	Br	C6D6	5	1a (0)	3a (41)	9a (56)
1b	Me	H	I	CDCl3	1	1b (0)	3b (46)	9b (35)
1b	Me	H	I	C6D6	3	1b (0)	3b (81)	9b (19)
2a	Ph	H	Br	CDCl3	1	2a (45)	4a (21)	9a (34)
2b	Ph	H	I	CDCl3	1	2b (30)	4b (10)	9b (56)
6a	Me	Me	Br	CDCl3	1	6a (100)	11a (0)	9a (0)

• ^a The yields were estimated in the ¹H NMR spectra using cyclohexane as internal standard.

Table 2. 1,2‐Silyl migration reactions in a flask to isolate 3 and 4

	R	X	Y	Solvent	Products	Yield (%)a^a Isolated yields.
1a	Me	H	Br	Hexane	3a	83
1b	Me	H	I	Hexane	3b	43
2a	Ph	H	Br	Hexane‐toluene	4a	40
2b	Ph	H	I	Hexane‐toluene	4b	38

• ^a Isolated yields.

2.3 Structures of 1‐halo‐8‐silylnaphthalenes

The driving force for silyl migration may be relief of steric compression, as discussed for the reactions of 1,2‐disilylbenzene, 1,2‐disilylnaphthalene, and 1‐silylnaphthalene.2, 10, 3

Steric repulsion in 1 was supported by the NMR spectra. The ¹H resonances of the proton on the silicon atom in 1 and 2 were deshielded, whereas the ²⁹Si resonances of the silicon atom of the hydrosilyl group were shielded compared with the corresponding values of silylnaphthalenes 11 and 12, respectively, as shown in Table 3. This behavior can be explained in terms of the van der Waals effect11; the steric repulsion between the hydrosilyl group and the halogen atom causes a decrease in the electron density on the hydrogen atom and an increase in the electron density on the silicon atom. The van der Waals effect is also indicated by the IR spectra (Table 3); the ν(Si‐H) absorptions in 1 and 2 appeared at higher frequencies than those in 11 and 12, respectively.

Table 3. Selected ¹H and ²⁹Si resonances in 1, 2, 11, and 12

	R	X	Y	^1H (δ)	^29Si (δ)	ν (Si‐H) (cm^−1)
1a	Me	H	Br	5.19	−13.43	2164
1b	Me	H	I	5.66	−18.78	2158
2a	Ph	H	Br	6.43	−16.98	2162
2b	Ph	H	I	6.90	−17.83	2137
11	Me	H	H	4.96	−20.41	2123
12	Ph	H	H	5.92	−20.57	2108

The molecular structures of 2a and 2b were revealed by X‐ray crystallographic analysis (Figures 2 and 3).12, 13 Each molecule is distorted owing to the steric repulsion between the halogen atom and the silyl group. The substituents are not coplanar with the naphthalene ring. The dihedral angles of Si‐C8‐C1‐Y are 23.6° (Y = Br (2a)) and 27.5° (Y = I (2b)). The atomic distance between Si and Y (3.22 Å (Y = Br (2a)); 3.42 Å (Y = I (2b)) is longer than the mean distance between C1 and C8 on the naphthalene ring.

Figure 2

Molecular structure of 2a; thermal ellipsoids are drawn at the 30% probability level and H atoms, except for H1, are omitted for clarity

Figure 3

Molecular structure of 2b; thermal ellipsoids are drawn at the 30% probability level and H atoms, except for H1, are omitted for clarity

DFT calculations also supported the existence of steric repulsion.14 The structures of 1b and 3b were optimized at the B3LYP/6‐31G(d)+LANL2DZ level of theory, as shown in Figure 4. 7‐Silylnaphthalene 3b is more stable than 8‐silylnaphthalene 1b by 56.3 kcal/mol. 8‐Silylnaphthalene 1b is highly distorted, such extent that the dihedral angle of Si‐C8‐C1‐I is 24.4°. In contrast, 7‐silylnaphthalene 3b is almost planar, as the dihedral angle of Si‐C7‐C1‐I is 0°.

Figure 4

Optimized structures of 1b (left) and 3b (right)

2.4 Reaction mechanism of silyl migration

To gain further insight into the reaction mechanism of silyl migration, D‐labeling experiments were performed (Scheme 7). Deuterated silane 1a‐D was treated with I₂ under the conditions used for the nondeuterated compounds. In the presence of 4 mol% I₂, 3a‐D (56%), 9a‐D (5%), and 9a (37% yield) were obtained. In contrast, when 50 mol% I₂ was used, 9a‐D (52%) and 9a (43%) were obtained, but 3a‐D was not obtained.

Scheme 7

D‐labeling experiment for 1,2‐silyl migration in 1a‐D

According to the literature2, 10, 3 and the D‐labeling experiments, the reaction mechanism is postulated as follows (Scheme 8). (a) Reaction of 1‐D_Si with catalytic amounts of I₂ affords iodosilylnaphthalene 1‐I and DI.15 (b) Reaction of 1‐D_Si with DI yields Wheland complex IntA‐D_SiD.16 (c) A hydrosilyl group in IntA‐D_SiD migrates to the cationic carbon at the 7‐position to form IntB‐D_SiD. (d) Iodide (or another nucleophile) attacks the hydrogen at the 7‐position in IntB‐D_SiD to afford 3‐D_SiD. Alternatively, iodide (or another nucleophile) attacks the silyl group in IntA‐D_SiD to produce desilylated naphthalene 9‐D. After DI is consumed, 1‐D_Si reacts with HI to form IntA‐D_SiH, IntB‐D_SiH, and finally 3‐D_SiH in manners similar to the reaction of 1‐D_Si with DI. D‐incorporation into the naphthalene ring is induced only by DI, which is generated by the reaction of 1‐D_Si and I₂ in the initial step. Thus, the extent of D‐incorporation depends on the amount of I₂.

Scheme 8

Plausible mechanism of 1,2‐silyl migration in 1‐D

3 CONCLUSION

1‐Halo‐8‐(hydrosilyl)naphthalenes 1 and 2 underwent 1,2‐silyl migration to afford 1‐halo‐7‐silylnaphthalenes 3 and 4. The driving force for the silyl migration may be relief of steric compression, which was supported by the NMR spectra and DFT calculations. D‐labeling experiments were also performed to obtain further insight into the reaction mechanism of silyl migration. It was postulated that the migration process may include four steps: (a) generation of acid (HI) by the reaction of the hydrosilane with I₂, (b) protonation of the naphthalene ring, (c) silyl group migration in the protonated intermediate, and (d) deprotonation of the naphthalene ring.

4 EXPERIMENTAL SECTION

4.1 General considerations

¹H (400 MHz), ¹³C (100 MHz), and ²⁹Si (79.5 MHz) NMR spectra were recorded using a Bruker Avance III 400 spectrometer. ¹H and ¹³C chemical shifts were referenced to the internal CDCl₃ (δ(¹H) = 7.26 ppm; δ(¹³C) = 77.00 ppm). ²⁹Si chemical shifts were referenced to external tetramethylsilane (δ = 0 ppm). The mass spectra (EI) were recorded at 70 eV using a JEOL JMS‐Q1000GC Mk II mass spectrometer in our laboratory. Column chromatography was performed using silica gel 60N (63‐210 mesh, Kanto Chemical Co., Inc., Tokyo, Japan). Thin layer chromatography (TLC) was performed on plates of silica gel 60 F₂₅₄ (Merck, Darmstadt, Germany).

4.2 Materials

1‐Bromonaphthalene (Tokyo Chemical Industry Co., Ltd., Tokyo, Japan), n‐butyllithium in hexane (Kanto Chemical Co., Inc.), chlorodiphenylsilane (Shin‐Etsu Chemical Co., Ltd., Tokyo, Japan), lithium aluminum hydride (Wako Pure Chemical Industries, Ltd., Osaka, Japan), and TCCA (Wako Pure Chemical Industries, Ltd.) were used as received. Chlorodimethylsilane (Tokyo Chemical Industry Co., Ltd.) was distilled under a nitrogen atmosphere over calcium hydride. Chlorotrimethylsilane (Tokyo Chemical Industry Co., Ltd.) was treated with small pieces of sodium under a nitrogen atmosphere to remove dissolved HCl, and the supernatant was used. Triethylamine (Tokyo Chemical Industry Co., Ltd.) was distilled under a nitrogen atmosphere over calcium hydride. 1,8‐Dibromonaphthalene and 1,8‐diiodonaphthalene were prepared according to the literature methods.4, 5 THF and Et₂O were distilled under a nitrogen atmosphere over sodium benzophenone ketyl. Hexane was distilled under a nitrogen atmosphere over sodium. All reactions were carried out under an inert gas atmosphere.

4.3 Experimental details

4.3.1 1‐Bromo‐8‐(dimethylsilyl)naphthalene (1a) (CAS No. 1313372‐01‐8)

A solution of n‐BuLi in hexane (1.64 mol/L, 2.68 mL, 4.40 mmol) was added dropwise to a solution of 1,8‐dibromonaphthalene (7a) (1.14 g, 4.00 mmol) in Et₂O (40 mL) at −78°C. After the reaction mixture was stirred at this temperature for 1 hour, chlorodimethylsilane (0.50 mL, 4.50 mmol) was added via a syringe. Then, the mixture was warmed to room temperature. The solvent was removed in vacuo, and the residue (1161 mg) was subjected to column chromatography on silica gel eluted with hexane (R_f = 0.52) to give 1a (891 mg, 84% yield) as a colorless oil. ¹H NMR (CDCl₃) δ 0.60 (d, J = 4 Hz, 6H), 5.19 (sept, J = 4 Hz, 1H), 7.30 (t, J = 8 Hz, 1H), 7.46 (t, J = 8 Hz, 1H), 7.84 (dd, J = 8 Hz, J = 1 Hz, 1H), 7.87 (dd, J = 8 Hz, J = 1 Hz, 1H), 7.88 (dd, J = 8 Hz, J = 1 Hz, 1H), 8.02 (dd, J = 8 Hz, J = 1 Hz, 1H). ¹³C{¹H} NMR (CDCl₃) δ 0.94, 123.16, 125.43, 125.83, 129.43, 131.25, 132.26, 136.00, 136.63, 136.76, 138.49. ²⁹Si NMR (CDCl₃) δ −13.43 (d, ¹J_Si‐H = 199 Hz). MS(EI) m/z: 266 (M⁺[⁸¹Br], 28), 264 (M⁺[⁷⁹Br], 28), 251 (M⁺[⁷⁹Br]–Me, 98), 249 (M⁺[⁸¹Br]–Me, 100), 169 (M⁺–Me–Br, 71). IR (Nujol) (cm⁻¹) 3025, 2723, 2164 (ν(Si‐H)), 1597, 1377, 1306, 1250, 1149, 980, 918, 772, 723.

4.3.2 1‐Iodo‐8‐(dimethylsilyl)naphthalene (1b) (CAS No. 105090‐68‐4)

A solution of n‐BuLi in hexane (1.60 mol/L, 2.06 mL, 3.30 mmol) was added dropwise to a solution of 1,8‐diiodonaphthalene (7b) (1.14 g, 3.00 mmol) in THF–Et₂O (20 mL/20 mL) at −78°C. After the reaction mixture was stirred at this temperature for 1 hour, chlorodimethylsilane (0.39 mL, 3.60 mmol) was added via a syringe. Then, the mixture was warmed to room temperature. The reaction mixture was washed with brine, dried over Na₂SO₄, and concentrated in vacuo to give 1b (850 mg, 91% yield) as a yellow oil. ¹H NMR (CDCl₃) δ 0.60 (d, J = 4 Hz, 6H), 5.66 (sept, J = 4 Hz, 1H), 7.12 (dd, J = 8 Hz, J = 7 Hz, 1H), 7.43 (dd, J = 8 Hz, J = 7 Hz, 1H), 7.79 (dd, J = 8 Hz, J = 1 Hz, 1H), 7.84 (dd, J = 7 Hz, J = 1 Hz, 1H), 7.96 (dd, J = 7 Hz, J = 1 Hz, 1H), 8.28 (dd, J = 7 Hz, J = 1 Hz, 1H). ¹³C {¹H} NMR (CDCl₃) δ 1.22, 96.96, 125.07, 126.33, 130.29, 131.43, 135.77, 138.37, 138.73, 139.80, 141.02. ²⁹Si NMR (CDCl₃) δ −18.78 (d, ¹J_Si‐H = 201 Hz). MS(EI) m/z: 312 (M⁺, 27), 311 (M⁺–H, 27), 297 (M⁺–Me, 100), 169 (M⁺–I, 46). IR (Nujol) (cm⁻¹) 3053, 2158 (ν(Si‐H)), 1594, 1540, 1304, 1248, 1142, 1047, 974, 893, 783, 652.

4.3.3 1‐Bromo‐8‐(diphenylsilyl)naphthalene (2a)

This compound was prepared in a manner similar to that used for 1a and obtained as a pale yellow solid after column chromatography on silica gel eluted with hexane (R_f = 0.25). The solid was recrystallized from hexane to give 2a (1.28 g) as a pale yellow crystal in 82% yield. ¹H NMR (CDCl₃) δ 6.43 (s, 1H), 7.30‐7.42 (m, 8H), 7.49‐7.52 (m, 4H), 7.78 (dd, J = 7 Hz, J = 1 Hz, 1H), 7.82 (dd, J = 7 Hz, J = 1 Hz, 1H), 7.86 (dd, J = 8 Hz, J = 1 Hz, 1H), 7.91 (dd, J = 8 Hz, J = 1 Hz, 1H). ¹³C{¹H} NMR (CDCl₃) δ 123.70, 125.43, 126.09, 127.88, 129.14, 129.43, 131.86, 132.45, 134.30, 135.63, 136.09, 137.05, 141.82 (signals corresponding to the two ipso carbons in the phenyl groups were not observed). ²⁹Si NMR (CDCl₃) δ −16.98 (d, ¹J_Si‐H = 213 Hz). MS(EI) m/z: 389 (M⁺[⁸¹Br], 4), 387 (M⁺[⁷⁹Br], 4), 311 (M⁺–Br, 100), 231 (M⁺–Br–Ph, 81). IR (Nujol) (cm⁻¹) 2725, 2162 (ν(Si‐H)), 1585, 1309, 1190, 1115, 974, 868, 818, 731, 696. Anal. Calcd for C₂₂H₁₇BrSi: C, 67.86; H, 4.40; Found: C, 67.73; H, 4.42.

4.3.4 1‐Iodo‐8‐(diphenylsilyl)naphthalene (2b)

This compound was prepared in a manner similar to that used for 1b and obtained as a pare yellow solid after column chromatography on silica gel eluted with hexane (R_f = 0.30). The solid was recrystallized from hexane to give 2b (1.27 g) as a pale yellow crystal in 73% yield. ¹H NMR (CDCl₃) δ 6.90 (s, 1H), 7.15 (t, J = 8 Hz, 1H), 7.31‐7.41 (m, 7H), 7.47‐7.49 (m, 4H), 7.76 (d, J = 7 Hz, 1H), 7.84 (dd, J = 8 Hz, J = 1 Hz, 1H), 7.88 (dd, J = 8 Hz, J = 1 Hz, 1H), 8.24 (dd, J = 7 Hz, J = 1 Hz, 1H). ¹³C{¹H} NMR (CDCl₃) δ 97.58, 125.08, 126.60, 127.91, 129.15, 130.33, 132.21, 134.30, 135.77, 137.23, 140.21, 141.21, 142.23 (signals corresponding to the two ipso carbons in the phenyl groups were not observed). ²⁹Si NMR (CDCl₃) δ −17.83 (d, ¹J_Si‐H = 215 Hz). MS(EI) m/z 435 (M⁺–H, 4), 358 (M⁺–Ph, 23), 307 (M⁺–I, 11), 231 (M⁺–Ph–I, 100). IR (Nujol) (cm⁻¹) 2727, 2137 (ν(Si‐H)), 1604, 1300, 985, 857, 777, 729, 687. Anal. Calcd for C₂₂H₁₇ISi: C, 60.55; H, 3.93; Found: C, 60.36; H, 4.01.

4.3.5 1‐Bromo‐8‐[(methoxy)dimethylsilyl]naphthalene (5a)

A solution of 1a (248 mg, 0.94 mmol) in hexane (1.5 mL) was added dropwise to a suspension of TCCA (217 mg, 0.94 mmol) in hexane (0.5 mL) at 0°C, and the reaction mixture was stirred at room temperature for 6 hour. After filtering the reaction mixture, the solvent was removed in vacuo to afford 1‐bromo‐8‐[(chloro)dimethylsilyl]naphthalene (8) as a colorless oil. THF (2 mL), MeOH (0.04 mL, 1.06 mmol), and Et₃N (0.15 mL, 1.16 mmol) were added to the oil, which was then stirred for 1 hour at room temperature. The solvent was removed in vacuo, and the residue (389 mg) was subjected to column chromatography on silica gel eluted with hexane‐AcOEt (20:1) (R_f = 0.50) to give 5a (180 mg, 65% yield) as a colorless oil. ¹H NMR (CDCl₃) δ 0.71 (s, 6H), 3.47 (s, 3H), 7.30 (dd, J = 8 Hz, J = 7 Hz, 1H), 7.51 (dd, J = 8 Hz, J = 7 Hz, 1H), 7.81‐7.85 (m, 2H), 7.87 (dd, J = 7 Hz, J = 1 Hz, 1H), 8.20 (dd, J = 7 Hz, J = 1 Hz, 1H). ¹³C{¹H} NMR (CDCl₃) δ 2.69, 50.55, 122.09, 125.40, 125.70, 129.40, 131.15, 132.03, 136.11, 136.21, 136.90, 137.64. ²⁹Si{¹H} NMR (CDCl₃) δ 6.73. MS(EI) m/z: 296 (M⁺[⁸¹Br], 8), 294 (M⁺[⁷⁹Br], 7), 281 (M⁺[⁸¹Br]–Me, 100), 279 (M⁺[⁷⁹Br]–Me, 98), 266 (M⁺[⁸¹Br]–2Me, 73), 264 (M⁺[⁷⁹Br]–2Me, 71), 215 (M⁺–Br, 91). IR (Nujol) (cm⁻¹) 3055, 1547, 1306, 1254, 1095, 978, 868, 814, 787. Anal. Calcd for C₁₃H₁₅BrOSi: C, 52.88; H, 5.12; Found: C, 52.64; H, 5.13.

4.3.6 1‐Bromo‐8‐(trimethylsilyl)naphthalene (6a) (CAS No. 124153‐82‐8)

A solution of n‐BuLi in hexane (1.64 mol/L, 0.67 mL, 1.10 mmol) was added dropwise to a solution of 1,8‐dibromonaphthalene (7a) (286 mg, 1.00 mmol) in THF (10 mL) at −78°C. After the reaction mixture was stirred at this temperature for 1 hour, chlorotrimethylsilane (0.15 mL, 1.20 mmol) was added via a syringe. Then, the mixture was warmed to room temperature. The solvent was removed in vacuo, and the residue (343 mg) was subjected to column chromatography on silica gel eluted with hexane (R_f = 0.63) to give 6a (217 mg, 78% yield) as a colorless oil. ¹H NMR (CDCl₃) δ 0.60 (s, 9H), 7.30 (dd, J = 8 Hz, J = 7 Hz, 1H), 7.45 (dd, J = 8 Hz, J = 7 Hz, 1H), 7.82 (dd, J = 7 Hz, J = 1 Hz, 1H), 7.84 (dd, J = 7 Hz, J = 1 Hz, 1H), 7.89 (dd, J = 7 Hz, J = 1 Hz, 1H), 8.01 (dd, J = 7 Hz, J = 1 Hz, 1H). ¹³C{¹H} NMR (CDCl₃) δ 4.57, 122.35, 125.13, 125.61, 129.46, 130.83, 132.30, 136.06, 137.02, 137.65, 138.62. ²⁹Si{¹H} NMR (CDCl₃) δ −2.70. MS(EI) m/z: 280 (M⁺[⁸¹Br], 12), 278 (M⁺[⁷⁹Br], 11), 265 (M⁺[⁸¹Br]–Me, 100), 263 (M⁺[⁷⁹Br]–Me, 98), 183 (M⁺–Me–Br, 87). IR (Nujol) (cm⁻¹) 3055, 1547, 1493, 1304, 1250, 1192, 978, 870, 834, 766, 702.

4.3.7 1‐Bromo‐8‐[(deuterio)dimethylsilyl]naphthalene (1a‐D)

A solution of 5a (480 mg, 1.60 mmol) in THF (4 mL) was added dropwise to a suspension of LiAlD₄ (68 mg, 1.60 mmol) in THF (2 mL) at 0°C, and the reaction mixture was stirred at room temperature for 4 hour. Me₃SiCl (0.20 mL, 1.60 mmol) was added dropwise to the reaction mixture at 0°C, and the reaction mixture was stirred at room temperature for 2 hour. After the solvents were removed in vacuo; the residue was diluted with hexane (10 mL) and filtered. The filtrate was subjected to bulb‐to‐bulb distillation (110‐120°C/1.5 mm Hg) to give 1a‐D (128 mg, 30% yield) as a colorless oil. The D‐labeling was evidenced by comparison with the spectra of 1a. ¹H NMR (CDCl₃) δ 0.62 (s, 6H), 7.31 (t, J = 8 Hz, 1H), 7.47 (dd, J = 8 Hz, J = 7 Hz, 1H), 7.84 (dd, J = 8 Hz, J = 1 Hz, 1H), 7.87 (dd, J = 7 Hz, J = 1 Hz, 1H), 7.89 (dd, J = 8 Hz, J = 1 Hz, 1H), 8.05 (dd, J = 7 Hz, J = 1 Hz, 1H). ¹³C{¹H} NMR (CDCl₃) δ 0.86, 123.16, 125.42, 125.81, 129.42, 131.24, 132.23, 135.98, 136.62, 136.71, 138.50. ²⁹Si NMR (CDCl₃) δ −13.62 (t, ¹J_Si‐D = 152 Hz). MS(EI) m/z: 267 (M⁺[⁸¹Br], 22), 265 (M⁺[⁷⁹Br], M⁺[⁸¹Br]–H, 38), 263 (M⁺[⁷⁹Br]–H, 18), 252 (M⁺[⁸⁹Br]–H, 98), 250 (M⁺[⁷⁹Br]–Me, 100), 186 (M⁺–Me–Br, 75). IR (Nujol) (cm⁻¹) 3055, 2898, 1564 (ν(Si‐D)), 1493, 1417, 1358, 1306, 1248, 1192, 1051, 978, 866, 823, 795, 768, 706.

4.3.8 1‐Bromo‐7‐(dimethylsilyl)naphthalene (3a)

A solution of 1a (106 mg, 0.40 mmol) and iodine (4 mg, 0.02 mmol, 5 mol%) in hexane (1.0 mL) was stirred at room temperature for 1 hour. The reaction mixture was washed with saturated Na₂S₂O₃ solution (0.5 mL) and dried over Na₂SO₄. The solvent was removed in vacuo. The residue (91 mg) was subjected to column chromatography on silica gel eluted with hexane (R_f = 0.58) to give 3a (46 mg, 43% yield) as colorless oil. ¹H NMR (CDCl₃) δ 0.47 (d, J = 4 Hz, 6H), 4.60 (sept, J = 4 Hz, 1H), 7.33 (t, J = 8 Hz, 1H), 7.67 (dd, J = 8 Hz, J = 1 Hz, 1H), 7.78‐7.83 (m, 3H), 8.44 (d, J = 1 Hz, 1H). ¹³C{¹H} NMR (CDCl₃) δ −3.75, 123.06, 126.67, 127.37, 127.81, 130.04, 131.06, 131.24, 133.52, 135.03, 137.04. ²⁹Si NMR (CDCl₃) δ −16.04 (d, ¹J_Si‐H = 190 Hz). MS(EI) m/z: 266 (M⁺[⁸¹Br], 31), 264 (M⁺[⁷⁹Br], 30), 251 (M⁺[⁸¹Br]–Me, 100), 249 (M⁺[⁷⁹Br]–Me, 99), 169 (M⁺–Me–Br, 33). IR (Nujol) (cm⁻¹) 3053, 2958, 2900, 2723, 2121 (ν(Si‐H)), 1545, 1415, 1354, 1306, 1250, 1150, 881, 825, 761. Anal. Calcd for C₁₂H₁₃BrSi: C, 54.34; H, 4.94; Found: C, 54.22; H, 4.80.

4.3.9 1‐Iodo‐7‐(dimethylsilyl)naphthalene (3b)

A solution of 1b (125 mg, 0.40 mmol) and iodine (4 mg, 0.02 mmol, 5 mol%) in hexane (1.0 mL) was stirred at room temperature for 1 hour. The reaction mixture was washed with saturated Na₂S₂O₃ solution (0.5 mL) and dried over Na₂SO₄. The solvent was removed in vacuo. The residue (123 mg) was subjected to column chromatography on silica gel eluted with hexane (R_f = 0.48) to give 3b (106 mg, 83% yield) as a yellow oil. ¹H NMR (CDCl₃) δ 0.46 (d, J = 4 Hz, 6H), 4.59 (sept, J = 4 Hz, 1H), 7.19 (dd, J = 8 Hz, J = 7 Hz, 1H), 7.64 (dd, J = 8 Hz, J = 1 Hz, 1H), 7.73 (d, J = 8 Hz, 1H), 7.82 (d, J = 8 Hz, 1H), 8.09 (dd, J = 7 Hz, J = 1 Hz, 1H), 8.26 (d, J = 1 Hz, 1H). ¹³C{¹H} NMR (CDCl₃) δ −3.76, 100.00, 127.33, 127.58, 128.87, 131.09, 133.44, 134.57, 137.45, 137.56, 138.67. ²⁹Si NMR (CDCl₃) δ −16.21 (d, ¹J_Si‐H = 190 Hz). MS(EI) m/z: 312 (M⁺, 51), 297 (M⁺–Me, 25), 185 (M⁺–I, 100). IR (Nujol) (cm⁻¹) 3051, 2119 (ν(Si‐H)), 1925, 1585, 1303, 1252, 1200, 1093, 879, 788, 642. Anal. Calcd for C₁₂H₁₃ISi: C, 46.16; H, 4.20; Found: C, 45.87; H, 3.98.

4.3.10 1‐Bromo‐7‐(diphenylsilyl)naphthalene (4a)

A solution of 2a (156 mg, 0.4 mmol) and iodine (4 mg, 0.02 mmol, 5 mol%) in hexane–toluene (1.0 mL/1.0 mL) was stirred at room temperature for 1 hour. The reaction mixture was washed with saturated Na₂S₂O₃ solution (0.5 mL) and dried over Na₂SO₄. The solvents were removed in vacuo. The residue (110 mg) was subjected to column chromatography on silica gel eluted with hexane (R_f = 0.20) to give 4a (59 mg, 38% yield) as a yellow solid. ¹H NMR (CDCl₃) δ 5.67 (s, 1H), 7.36 (t, J = 8 Hz, 1H), 7.40‐7.49 (m, 6H), 7.64‐7.67 (m, 4H), 7.70 (d, J = 8 Hz, 1H), 7.79‐7.84 (m, 3H), 8.57 (s, 1H). ¹³C{¹H} NMR (CDCl₃) δ 123.24, 127.08, 127.64, 127.81, 128.14, 129.97, 130.16, 131.36, 132.14, 132.92, 133.01, 135.28, 135.84, 135.98. ²⁹Si NMR (CDCl₃) δ −17.60 (d, ¹J_Si‐H = 203 Hz). MS(EI) m/z: 390 (M⁺[⁸¹Br], 29), 388 (M⁺[⁷⁹Br], 28), 309 (M⁺–Br, 100). IR (Nujol) (cm⁻¹) 2723, 2671, 2127 (ν(Si‐H)), 1587, 1377, 1109, 968, 802, 729. Anal. Calcd for C₂₂H₁₇BrSi: C, 67.86; H, 4.40; Found: C, 67.85; H, 4.43.

4.3.11 1‐Iodo‐7‐(diphenylsilyl)naphthalene (4b)

This compound was prepared in a manner similar to the used for 4a and obtained as a yellow solid (70 mg, 40% yield) after column chromatography on silica gel eluted with hexane (R_f = 0.18). ¹H NMR (CDCl₃) δ 5.64 (s, 1H), 7.21 (t, J = 8 Hz, 1H), 7.39‐7.48 (m, 6H), 7.60‐7.68 (m, 5H), 7.74 (d, J = 8 Hz, 1H), 7.82 (d, J = 8 Hz, 1H), 8.10 (dd, J = 7 Hz, J = 1 Hz, 1H), 8.36 (s, 1H). ¹³C{¹H} NMR (CDCl₃) δ 100.15, 127.73, 127.82, 128.14, 128.86, 129.97, 132.17, 132.91, 133.42, 133.62, 134.85, 135.86, 137.67, 141.15. ²⁹Si NMR (CDCl₃) δ −17.83 (d, ¹J_Si‐H = 201 Hz). MS(EI) m/z: 436 (M⁺, 36), 358 (M⁺–Ph, 26), 309 (M⁺–I, 100), 231 (M⁺–I–Ph, 57). IR (Nujol) (cm⁻¹) 2725, 2669, 2129 (ν(Si‐H)), 1589, 1377, 1109, 802, 729. Anal. Calcd for C₂₂H₁₇ISi: C, 60.55; H, 3.93; Found: C, 60.44; H, 3.96.

4.3.12 1‐(Dimethylsilyl)naphthalene (11) (CAS No. 30274‐80‐5)

A solution of n‐BuLi in hexane (1.64 mol/L, 2.59 mL, 4.24 mmol) was added dropwise to a solution of 1‐bromonaphthalene (800 mg, 3.86 mmol) in Et₂O (10 mL) at 0°C. After the reaction mixture was stirred at this temperature for 1 hour, chlorodimethylsilane (0.50 mL, 4.59 mmol) was added via a syringe. Then, the mixture was warmed to room temperature. The solvent was removed in vacuo, and the residue (1157 mg) was subjected to column chromatography on silica gel eluted with hexane (R_f = 0.53) to give 11 (811 mg, 79% yield) as a colorless oil. ¹H NMR (CDCl₃) δ 0.57 (d, J = 4 Hz, 6H), 4.96 (sept, J = 4 Hz, 1H), 7.51‐7.61 (m, 3H), 7.80 (dd, J = 7 Hz, J = 1 Hz, 1H), 7.91‐7.95 (m, 2H), 8.20 (dd, J = 8 Hz, J = 1 Hz, 1H). ¹³C{¹H} NMR (CDCl₃) δ −3.26, 125.15, 125.51, 125.90, 127.58, 128.94, 129.99, 133.20, 133.61, 135.60, 136.96. ²⁹Si NMR (CDCl₃) δ −20.41 (d, ¹J_Si‐H = 204 Hz). MS(EI) m/z: 186 (M⁺, 66), 171 (M⁺–Me, 100). IR (Nujol) (cm⁻¹) 3048, 2123 (ν(Si‐H)), 1506, 1376, 1250, 1146, 985, 883, 839, 779.

4.3.13 1‐(Diphenylsilyl)naphthalene (12) (CAS No. 100447‐84‐5)

This compound was prepared in a manner similar to that used for 11 and obtained as a colorless solid after column chromatography on silica gel eluted with hexane (R_f = 0.33). The solid was recrystallized from hexane to give 12 (969 mg) as a pale yellow crystal in 81% yield. ¹H NMR (CDCl₃) δ 5.92 (s, 1H), 7.41‐7.50 (m, 9H), 7.59‐7.64 (m, 5H), 7.89 (d, J = 8 Hz, 1H), 7.94 (d, J = 8 Hz, 1H), 8.07 (d, J = 8 Hz, 1H). ¹³C{¹H} NMR (CDCl₃) δ 125.24, 125.72, 126.16, 128.09, 128.25, 128.81, 129.80, 130.79, 131.42, 133.23, 133.27, 135.98, 136.83, 137.37. ²⁹Si NMR (CDCl₃) δ −20.57 (d, ¹J_Si‐H = 200 Hz). MS(EI) m/z: 310 (M⁺, 82), 231 (M⁺–Ph, 100). IR (Nujol) (cm⁻¹) 2727, 2663, 2108 (ν(Si‐H)), 1587, 1305, 1109, 982, 787, 771, 731, 698.

4.3.14 Typical procedure for NMR experiments: reaction of 1‐halo‐8‐silylnaphthalenes with I₂ in CDCl₃

To a solution of a 1‐halo‐8‐silylnaphthalene (0.040 mmol) and cyclohexane (20 μL) in CDCl₃ (0.60 mL) in a J. Young NMR tube was added I₂ (0.5 mg, 2.0 μmol) in one portion at room temperature. The reaction mixture was shaken at room temperature for 1 minute, and the sample was directly subjected to ¹H NMR spectroscopy. The yields of the products were estimated from the integral ratios using cyclohexane as an internal standard.

4.4 X‐ray crystallographic analysis

X‐ray crystallographic data for 2a and 2b were collected using a SMART APEX‐II CCD diffractometer with graphite‐monochromated Mo‐K_α radiation (λ = 0.71073 Å) at 173 K at the Department of Chemistry, Graduate School of Science, Hiroshima University. The structures were solved by direct methods using SIR 9712 and refined by a full‐matrix least‐squares procedure based on F² with SHELX‐97.13 All non‐hydrogen atoms were refined anisotropically. Hydrogen atoms were located at the expected positions by a geometrical calculation and refined isotropically or found on the difference Fourier map and refined isotropically.

Crystal data for 2a: C₂₂H₁₇BrSi, fw 389.35, monoclinic, P2₁/c (No. 14), a = 10.1994(7) Å, b = 16.3064(12) Å, c = 11.1616(8) Å, β = 107.9380(10)°, V = 1766.1(2) Å³, Z = 4, D_calcd = 1.464 g/cm³, R(I > 2σ(I)) = 0.0221, R_w(all data) = 0.0608, GOF = 1.033, T = 173 K.

Crystal data for 2b: C₂₂H₁₇ISi, fw 436.34, monoclinic, P2₁/c (No. 14), a = 10.2281(9) Å, b = 16.1277(14) Å, c = 11.3827(10) Å, β = 106.6440(10)°, V = 1799.0(3) Å³, Z = 4, D_calcd = 1.611 g/cm³, R(I > 2σ(I)) = 0.0182, R_w(all data) = 0.0485, GOF = 1.087, T = 173 K.

CCDC‐1842169 (2a) and CCDC‐1842170 (2b) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

4.5 Computational methods

Computations were executed with the Gaussian 09 program package14 at Research Center for Computing and Multimedia Studies, Hosei University. The structures of 1b and 3b were optimized at the B3LYP/(6‐31G(d) for H, C, and Si; LANL2DZ for I) level of theory. The frequency calculations were carried out for each compound at the same level as in the structure optimization to confirm the absence of any imaginary frequencies.

ACKNOWLEDGMENTS

This work was partially supported by a Grant‐in‐Aid for Scientific Research on Innovative Areas “Stimuli‐responsive Chemical Species for the Creation of Functional Molecules” (15H00961) from the Ministry of Education, Culture, Sports, Science and Technology, Japan.

Note

1 The migration was observed even under nitrogen atmosphere, but it was slow (ca. 3 months).