A new entry to oxacycles via base-catalyzed endo mode cyclization of allenyl sulfoxides and sulfones.

[reaction: see text]. Treatment of the allenyl sulfoxides and sulfones possessing a proper delta-hydroxy appendage at the C-1 position with potassium tert-butoxide effected endo mode ring closure at the sp-hybridized carbon center of the allenyl moiety to provide the five- to eight-membered oxacycles in high yields.