Unexpected 1,5-dilithiation of chiral o-TMS blocked (dimethylamino)phenylmethylferrocene: an alternative approach to chiral ferrocenyl 1,5-diphosphanes.
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 Ph2PCl. The rhodium and copper complex of 12 catalyzed well the asymmetric allylic alkylation with a Grignard reagent and hydrogenation with the alpha-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 Ph2PCl.
Fukuzawa
Shin-ichi
S
Department of Applied Chemistry, Institute of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan. fukuzawa@kc.chuo-u.ac.jp
Yamamoto
Masahisa
M
Kikuchi
Satoshi
S