CHELATION-DIRECTED ASYMMETRIC LITHIATION AND C-SUBSTITUTION OF 1,2,4-BUTANETRIOL ACETONIDE

The 2,2,4,4-tetramethyl-1,3-oxazolidine-3-carboxylate) 1 of (S)-1,2-O- isopropylidene-1,2,4-butanetriol is readily deprotonated by sec-butyll ithium in ether with high lk-diastereoselectivity: The presumed bicycl ic chelate complex 2 . OEt(2) is trapped by various electrophiles to f orm optically active adducts 4 with > 95% diastereoselectivity, servin g as a synthetic equivalent for the unknown (1S,3S)-1,3,4-trihydroxybu tanide ion. External complexation of tertiary diamines can compete wit h the internal oxygen ligand, leading to modified stereoselectivities.