Unexpected 1,5-Dilithiation of Chiral o-TMS Blocked (Dimethylamino)phenylmethylferrocene: An Alternative Approach to Chiral Ferrocenyl 1,5-Diphosphanes

摘要

The 1,5-dilithiation of o-TMS blocked (dimethylamino)-phenylmethylferrocene 4 unexpectedly occurred even though one equimolar amount of, t-BuLi was used and the 1,5-dilithiated ferrocene 6 was trapped by iodine followed by removal of the TMS group to give the 1,5-diiodoferrocene 11 in a reasonable yield. The 1,5-diiodoferrocene 11 was converted into the diastereomer of Taniaphos 12 by sequential dilithiation and trapping with Ph_2PCl. The rhodium and copper complex of 12 catalyzed well the asymmetric allylic alkylation with a Grignard reagent and hydrogenation with the α-acetamidocinnamic acid ester, respectively, with high enantioselectivities. The methoxy 1,5-diphosphane 14, of which the enantiomer is known as a good ligand for the rhodium-catalyzed asymmetric hydrogenation, was obtained by the inversive substitution of the dimethylamino group of 11 by NaOMe and subsequent dilithiation and trapping with Ph_2PCl.