Photocycloadditions of 2‐(trimethylsilyloxy)‐1,3‐butadiene to 2‐cycloalkenones. Access to the basic pentalenolactone skeleton

Abstract

Abstract The [2 + 2] Photocycloaddition of 2‐(trimethylsilyloxy)‐1,3‐butadiene to a number of 2‐cycloalkenones proved to be quite a general reaction leading to good yields of the cycloadducts (Table) . This finding is surprising since dienes, in general, are better known as quenchers of enone triplets rather than as photochemical reactants. Both the high substrate concentrations, which can be employed in these cycloadditions, and the remarkable regio and stereoselectivity of the processes qualify them as valuable for syntheses. In a first application, the photoproducts 1a, b were transformed in three steps into a viable precursor 4 of the pentalenolactone‐G and ‐H antibiotics.