MOLECULAR STRUCTURE AND PHOTODECARBONYLATION OF 2,3,4,5‐ TETRAPHENYLCYCLOPENTANONE

Clemmensen reduction of tetracyclone yields r‐2,t‐3,t‐4,c‐5‐tetraphenylcyclopentanone, the structure of which was established by x‐ray crystallography. Photodecarbonylation of this molecule results in the formation of cis‐ and trans‐stilbenes and minor amounts of tetraphenykyclobutane. The stilbenes are initially formed in comparable yield, but secondary photoisomerization results in cw‐rich mixtures. Stepwise photodecarbonylation is proposed to yield triplet meso‐ 1,2,3,4‐tetraphenylbutane‐diyl which undergoes nonstereoselective elimination in preference to cyclization. The intermediacyof the same biradical in the photodimerization stilbene can be effectively eliminated on the basis of stereochemical evidence.