New methods for the stereoselective synthesis of 2-hydroxy-3,4-dienoates and functionalized 2,5-dihydrofurans

Titanium enolates of 3,4-dienoates 3 were formed by treatment with LDA and Cp2TiCl2 and oxidized with dimethyl dioxirane to furnish the allenic hydroxyesters 4 with up to 90% diastereoselectivity. Smooth cyclization to the functionalized 2,5-dihydrofurans 5 was accomplished with complete axis to center chirality transfer by treatment with HCl gas in chloroform.