Chelation-Directed Asymmetric Lithiation and C-Substitution of 1,2,4-Butanetriol Acetonide

Abstract

The 4-O-(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-butyllithium in ether with high lk-diastereoselectivity: The presumed bicyclic chelate complex 2⋅OEt 2 is trapped by various electrophiles to form optically active adducts 4 with > 95% diastereoselectivity, serving as a synthetic equivalent for the unknown (1S,3S)-1,3,4-trihydroxybutanide ion. External complexation of tertiary diamines can compete with the internal oxygen ligand, leading to modified stereoselectivities.