Photodecarbonylation of chiral cyclobutanones

Article abstract of DOI:10.1139/v97-060

Triplet photosensitized irradiation of 2(S),3(R)-bis[(benzoyloxy)methyl]cyclobutanone gave optically pure (-)E-1(S),2(S)-bis(benzoyloxymethyl)cyclopropaneas a major product in the nonpolar fraction along with its stereoisomer and cycloelimination products. The absolute stereochemistry of the chiral cyclopropane was established by independent synthesis and X-ray crystal structure determination of a synthetic precursor. The distribution of decarbonylation and cycloelimination products was inversely dependent on the concentration of the substrate. Irradiation of the same ketone in tetrahydrofuran or benzene gave mostly cycloelimination products. Addition of Michler's ketone increased the ratio of photodecarbonylation, suggesting a triplet state pathway for this process. This was corroborated by the addition of dicyanoethylene, which showed significant quenching of photodecarbonylation. Irradiation of 2(S)-[(benzoyloxy)methyl]cyclobutane in acetone gave the corresponding cyclopropane as the principal product.