Phosphine-catalyzed formal vinylogous aldol reaction of γ-methyl allenoates with aldehydes: Easy access to 1,3-dioxanes and dienols

A phosphine-catalyzed formal vinylogous aldol reaction of γ-methyl allenoates with aldehydes is herein reported, in which the γ-methyl group is directly involved in the carbon-carbon bond formation. Under the catalysis of triarylphosphine (20 mol %) and in the presence of a protic additive, γ-methyl allenoates and aldehydes chemo- and stereoselectively produce functionalized 1,3-dioxanes or dienols in modest to good yields. These chemical transformations provide easy excess to oxy-functionalized enoates and dienoates under very mild conditions.