Photoannulation of 4,4-Dimethylcyclohex-2-en-1-one To 1,1-Diphenylethylene

This is the authors' abstract. We don't add key points for this paper.

The photoannulation of 4,4-dimethylcyclohex-2-en-1-one (DMC) to 1,1-diphenylethylene (DPE) results in the [2+2] formation of cyclobutanes exhibiting regio- and stereoselectivity. Additionally, regio- and stereoisomers of substituted octahydrophenanthrenes are produced. Formally, these are derived from alpha−ortho coupling of a 1,4-biradical, followed by rearomatization. From laser flash photolysis experiments, we conclude that the temporal absorbance profile observed following excitation of DMC in the presence of DPE is a composite of multiple triplet state transients that includes triplet state 1,1-diphenylethylene and likely includes a triplet state 1,4-biradical. This analysis of the transient data reveals energy transfer and product forming interactions between 3DMC and ground-state DPE. The present work renders our earlier interpretation [J. Am. Chem. Soc. 1996, 118, 8741],1 that the transient observed in this system was a 3DMC−DPE exciplex, unnecessary and unlikely.