The addition of titanium and lithium enolates 1 and 2 to γ-alkoxy enone 4 occurs in good yield with good stereoselectivities. 3,4 syn - 2,3 syn adducts 7 are obtained starting from the lithium enolate 2, whereas the 3,4 syn - 2,3 anti isomers 9 are formed using the titanium enolate 1. The levels of selectivity vary with the nature of the oxygen protecting group.
The reactions of the Ti ate enolate 1 and the Li enolate 2 with the chiral enone 3 were studied. Both reactions are moderately stereoselective, leading to the synthesis of the 2,3-anti-3,4-anti and the 2,3syn-3,4anti isomers with 78% and 82% selectivity, respectively. The addition of 1 appears to take place via an inverse demand Diels-Alderreaction, rather than a conjugate addition. This finding can