Enantioselective conjugate additions of aldoximes to 3-crotonoyl-2-oxazolidinone and 1-crotonoyl-3-phenyl-2-imidazolidinone catalyzed by the aqua complex between R,R-DBFOX/Ph and zinc(II) perchlorate

Conjugate addition reactions of aldoximes to 3-crotonoyl-2-oxazolidinone and to 1-crotonoyl-3-phenyl-2-imidazolidinone are accelerated in the presence of a catalytic amount of Lewis acids. Among the chiral metal complexes with DBFOX/Ph, BOX/Bu-t, BOX/Ph, BOX/o-OHBn, Pybox, or TADDOL ligands, the most effective thus far is the aqua complex derived from R,R-DBFOX/Ph and zinc(II) perchlorate. The reaction of 2-furancarbaldehyde oxime in dichloromethane in the presence of the R,R-DBFOX/Ph aqua complex derived from zinc(II) perchlorate hexahydrate (10 mol%) gave a moderate enantioselectivity of 64% ee at 0°C. Reactions using other metal complexes are also discussed.