Studies in polypropionate synthesis: High π-face selectivity in syn and anti aldol reactions of chiral boron enolates of lactate-derived ketones

Use of cHex2BCl / Me2NEt in the aldol reactions of the α′-benzoyloxy ketone 7 with aldehydes leads to high stereoselectivity (97–99.5% ds) for the crystalline anti adducts 11. Under similar conditions, the corresponding benzyl ether 6 favours formation of the syn adducts 9.