High diastereoselectivity in Hosomi-Sakurai reaction on metal-complexed acyclic enones: Role of out-of-plane coordination of Lewis acid

Efficient diastereocontrol is achieved in Hosomi-Sakurai reaction of flexib le acyclic enones anchored on arene-tricarbonylchromium template. Relative stereochemistry of groups in the products is compared with those obtained b y allylmagnesium bromide addition followed by an anionic oxy-Cope rearrange ment. The results indicate an endo-selective conjugate addition dictated by an out-of-plane bound Lewis acid in the Hosomi-Sakurai reaction, similar t o the trend established earlier for rigid substrate structures.