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Spirocyclopropanated Bicyclopropylidenes: Straightforward Preparation, Physical Properties, and Chemical Transformations


  • Preliminary communications: a) S. Zöllner, H. Buchholz, R. Boese, R. Gleiter, A. de Meijere, Angew. Chem.1991, 103, 1544–1546; Angew. Chem. Int. Ed. Engl.1991, 30, 1518–1520; b) M. von Seebach, S. I. Kozhushkov, R. Boese, J. Benet-Buchholz, D. S. Yufit, J. A. K. Howard, A. de Meijere, Angew. Chem.2000, 112, 2617–2620; Angew. Chem. Int. Ed.2000, 39, 2495–2498.


Perspirocyclopropanated bicyclopropylidene (6) was prepared in three steps from 7-cyclopropylidenedispiro[]heptane (4) (24 % overall) or, more efficiently, through dehalogenative coupling of 7,7-dibromo[3]triangulane (15) (82 %). This type of reductive dimerization turned out to be successful for the synthesis of (E)- and (Z)-bis(spiropentylidene) 14 (67 %) and even of the “third-generation” spirocyclopropanated bicyclopropylidene 17 (17 % overall from 15). Whereas the parent bicyclopropylidene 1 dimerized at 180 °C to yield [4]rotane, dimerization of 6 at 130 °C under 10 kbar pressure occured only with opening of one three-membered ring to yield the polyspirocyclopropanated (cyclopropylidene)cyclopentane derivative 19 (34 % yield), and at the elevated temperature the polyspirocyclopropanated 2-cyclopropylidene[3.2.2]propellane derivative 20 (25 % yield). Perspirocyclopropanated bicyclopropylidene 6 and the “third-generation” bicyclopropylidene 17 gave addition of bromine, hydrogen bromide, and various dihalocarbenes without rearrangement. The functionally substituted branched [7]triangulane 28 and branched dichloro-C2v-[15]triangulane 32 were used to prepare the perspirocyclopropanated [3]rotane (D3h-[10]triangulane) 49 (six steps from 6, 1.4 % overall yield) and the C2v-[15]triangulane 51 (two steps from 17, 41 % overall). Upon catalytic hydrogenation, the perspirocyclopropanated bicyclopropylidene 6 yielded 7,7′-bis(dispiro[]heptyl) (52) and, under more forcing conditions, 1,1′-bis(2,2,3,3-tetramethylcyclopropyl) (53). The bromofluorocarbene adduct 33 of 17 reacted with butyllithium to give the unexpected polyspirocyclopropanated 1,4-di-n-butyl-2-cyclopropylidenebicyclo[2.2.0]hexane derivative 37 as the main product (55 % yield) along with the expected “third-generation” perspirocyclopropanated dicyclopropylidenemethane 38 (21 % yield). Mechanistic aspects of this and the other unusual reactions are discussed. The structures of all new unusual hydrocarbons were proven by X-ray crystal structure analyses, and the most interesting structural and crystal packing features are presented.