PHOTODECARBONYLATION OF CHIRAL CYCLOBUTANONES

Triplet photosensitized irradiation of 2(S),3(R)-bis[(benzoyloxy)methy l]cyclobutanone gave optically pure (-)E-1(S),2(S)-bis(benzolyoxymethy l)cyclopropane as a major product in the nonpolar fraction along with its stereoisomer and cycloelimination products. The absolute stereoche mistry of the chiral cyclopropane was established by independent synth esis and X-ray crystal structure determination of a synthetic precurso r. The distribution of decarbonylation and cycloelimination products w as inversely dependent on the concentration of the substrate. Irradiat ion of the same ketone in tetrahydrofuran or benzene gave mostly cyclo elimination 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, whi ch showed significant quenching of photodecarbonylation. Irradiation o f 2(S)-[(benzoyloxy)methyl] cyclobutane in acetone gave the correspond ing cyclopropane as the principal product.