Stereoselective Synthesis of 3-Alkylated cis-1,2-Cyclobutanediols and Derivatives by Norrish-Yang Photocyclisation

The photocyclisation of enantiomerically pure α-heteroatom-substituted β-methyl butyrophenones 1 results in Norrish II cleavage and in Norrish II / Yang cyclisation products, cyclobutanols 2, the latter being formed with excellent diastereoselectivities and with relative yields which were strongly depending on the Hbonding activity of the α-substituent.