Free-radical based cycloalkanol synthesis and annulation from thioacetal precursors

A general procedure for the synthesis of diverse cyclopentanols via free-radical cyclization of unsaturated 1,3-oxathiolanes and 1,3-oxathiolan-5-ones is described. The scope of these reactions, including preliminary rate studies that indicate that the 1,3-oxathiolan-5-ones cyclize at a useful rate (1.4 × 106 M−1 s−1 at 80°C), has been examined. This permits the rapid assembly, by intramolecular annulation, of various additional ring systems, including bicyclo[3.3.0]octanols, bicyclo[4.3.0]nonanols, and bicyclo[3.2.1]octanols for use in total synthesis. Key words: radical cyclization, oxathiolanes, oxathiolanones.