Conjugated Additions of Selenium Containing Enolates to Enones. Enantioselective Synthesis of delta-Oxo-alpha-Seleno Esters and their Facile Transformations

Titanium enolates derived from the methyl phenylselenoacetate and other acetates bearing a selenium containing chiral auxiliary have been employed to effect 1,4-addition reactions to enones. These reactions generate delta-oxo-alpha-Seleno esters in good chemical yields and with excellent regio- and diastereoselectivities. The results obtained clearly indicate that the Lewis acids, employed to activate the starting enones to the addition, greatly influence the reactivity and the stereochemical outcome of these reactions. TiCl4-complexation resulted particularly efficient in promoting the 1,4-addition. Simple manipulations of the organoselenium moiety allowed some enantiomerically pure delta-oxo-alpha-camphorselenoesters to be transformed into the corresponding delta-oxo-alpha-hydroxy or delta-oxo-alpha-allylesters or into trisubstituted tetrahydrofurans.