Stereocontrolled Syntheses of Polysubstituted 2,3‐Dihydro‐4<i>H</i>‐pyran‐4‐ones by cyclocondensation of β‐ acyloxy‐ketones

Abstract

Abstract syn ‐β‐Acyloxy‐ketones 6 and an anti ‐β‐acyloxy‐ketone 17 undergo smooth intramolecular enolate/ester condensations 6 → 18 and 17 → 19 when treated with TiCl 4 /EtN(i‐Pr) 2 . Thus, tri‐ and tetrasubstituted cis ‐ or trans ‐2,3‐dihydro‐4 H ‐pyran‐4‐ones are easily prepared in a stereoselective manner.