Stereoselective intermolecular [2 + 2]-photocycloaddition reactions of maleic anhydride: stereocontrolled and regiocontrolled access to 1,2,3-trifunctionalized cyclobutanes.

Short synthetic sequences commencing with the photosensitized [2 + 2]-cycloaddition reactions of maleic anhydride with either allyl alcohol or propargyl alcohol have been elaborated to provide access to 1,2,3-trisubstituted cyclobutanes with three differentiated one-carbon substituents and complementary stereochemical patterns. These intermediates were used to prepare three discrete stereo- and regioisomers of hydroxymethylated cyclobutane β-amino acids in orthogonally protected form.