Functionalized Alkylidenecyclobutanes from a Cyclopent‐2‐enone Substrate via a Tandem Photochemical Transformation and an Allylic Substitution Protocol.

A four‐step metal‐free procedure is described for the transformation of 4‐hydroxy‐2‐methylcyclopent‐2‐enone derivatives into highly functionalized E‐alkylidenecyclobutanes featuring oxygenated tetrasubstituted centers. The key intermediate is a (cyclobutenyl)propane‐1,3‐diol diester, easily accessed via a tandem photochemical reaction, which undergoes an original Brønsted acid‐catalyzed allylic substitution reaction with alcohols to give the title products with ester‐protected primary alcohol side chains. [ABSTRACT FROM AUTHOR]