Photochemical Cycloadditions

Abstract

The photochemical [2 + 2] cycloaddition reaction of alkenes, the light-induced cycloaddition of two carbon–carbon π-bonds to produce a cyclobutane, is a potentially highly useful reaction in organic synthesis since two new carbon–carbon bonds are formed and a maximum of four new stereocenters are introduced in the process. 1 Ciamician reported the first example in 1908 when he observed the formation of carvone camphor ( 2 ) on prolonged exposure of carvone ( 1 ) to Italian sunlight (equation 1). 2