Photochemical generation of ketenes from phenanthrene-based cyclobutanones

Various 9,10-cyclopropanated phenanthrenes have been shown previously to be viable photochemical precursors to many different types of carbenes. There is also one known example in the literature of a related approach used to generate diphenylketene from a phenanthrene-derived cyclobutanone in a laser flash photolysis study. In an effort to broaden the scope of this promising yet under-utilized method of ketene generation, the synthesis and characterization of several phenanthrene-based cyclobutanones, and their subsequent photolysis to produce a variety of ketenes, are presented in this report. The ketenes are produced, along with phenanthrene, by a formal 2 + 2 cyclo-reversion of the cyclobutanone moiety and have been intercepted by benzyl alcohol and benzyl amine to form the corresponding benzyl esters and amides respectively.