PHOTO-CHEMICAL STUDIES ON THE MECHANISM OF THE OXADI-PI-METHANE REARRANGEMENT - EXAMPLE OF A STEREOSPECIFIC REARRANGEMENT

The photochemistry of several 2-substituted-2-(l-cyclopentenyl)cyclopentanones 2 was studied. On direct irradiation, [1, 3] acyl migrations were observed and, in the case of the optically active derivative 2c, the migration was shown to be stereospecific in the forward direction, but some loss of optical purity was noted for the reverse reaction. Sensitized irradiations of 2 gave the oxadi-π-methane (ODPM) rearrangement products 6. The ODPM rearrangement of optically active 2c gave 6c with inversion of stereochemistry at the “methane” carbon. A detailed discussion is presented with particular emphasis given to the relationship of this study with other studies of the stereochemistry of these reactions. © 1979, American Chemical Society. All rights reserved.