Photolytic conversion of some bicyclo[3.2.0]heptanones into 3-hydroxy or 3-methoxy-2-oxabicyclo[3.3.0]octan-2-ones

Abstract

The ketones (1) and (7)–(9) gave the corresponding cyclic acetals (3), (4), and (12)–(17), respectively, on photolysis in methanol. Concurrent production of the alkenes (6) and (18)–(20) detracted from the potential synthetic utility of this process. However, photolysis of the ketones (8), (10), and (11) in aqueous tetrahydrofuran or aqueous acetonitrile led to a highly selective ring-expansion process, and consequently high yields of the corresponding γ-lactols (21)–(23).