Iron-Catalyzed Oxidative Mono- and Bis-Phosphonation of N,N-Dialkylanilines



The dehydrogenative α-phosphonation of substituted N,N-dialkylanilines by dialkyl H-phosphonates was achieved under mild conditions by using environmentally benign iron(II) chloride as catalyst and tert-butyl hydroperoxide as oxidant. The reaction proceeded in the presence of electron-donating (methoxy, methyl, benzyl) and electron-withdrawing ring-substitutents (bromo, carbonyl, carboxyl, m-nitro) in moderate to good yields. The X-ray crystal structure of N-(5,5-dimethyl-2-oxo-2λ5-[1,3,2]dioxaphosphinan-2-yl-methyl)-N-methyl-p-toluidine was determined. Bis-(4-(dimethylamino)phenyl)methane and bis-4,4′-(dimethylamino)benzophenone underwent bisphosphonation selectively by respective monophosphonation at the remote dimethylamino groups. Furthermore, the use of excess dialkyl H-phosphonate and oxidant allowed us to functionalize both methyl groups of N(CH3)2 in N,N-dimethyl-p-toluidine and N,N-dimethylaminomesidine, respectively, to obtain α,α′-bisphosphonatoamines in high yield.