Radical Cyclization of alpha-Bromo Aluminum Acetals onto Alkenes and Alkynes (Radic[Al] Process): A Simple Access to gamma-Lactols and 4-Methylene-gamma-Lactols

An efficient preparation of gamma-lactols and methylene-gamma-lactols is described. Highly acid-sensitive lactols are prepared in a concise manner by using a radical cyclization of aluminum acetals. The precursors for the radical reactions are readily prepared from allyl or propargyl alcohols and alpha-bromo acids. Functionalization of the resulting gamma-lactols and methylene-gamma-lactols can be achieved following isolation, leading to synthetically useful building blocks, such as 1,4-diols, 1,4-dienes, gamma-lactones, and polysubstituted tetrahydrofurans