Mt. Crimmins et K. Chaudhary, Titanium enolates of thiazolidinethione chiral auxiliaries: Versatile tools for asymmetric aldol additions, ORG LETT, 2(6), 2000, pp. 775-777
Asymmetric aldol additions using chlorotitanium enolates of thiazolidinethi
one propionates proceed with high diastereoselectivity for the "Evans" or "
non-Evans" syn product depending on the nature and amount of the base used.
With (-)-sparteine as the base, selectivities of 97:3 to >99:1 were obtain
ed for the Evans syn products with 2 equivalents of base and for the non-Ev
ans syn when 1 equiv of base was employed. The thiazolidinethione auxiliari
es are easily removed, and the aldol adducts can be readily transformed to
various functional groups. Even direct reduction to the aldehyde with diiso
butylaluminum hydride is possible.