Titanium enolates of thiazolidinethione chiral auxiliaries: Versatile tools for asymmetric aldol additions

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.