Intramolecular Chemistry of ß-acetoxyethylidene and Photochemical Generation of Vinylidenes

Jennifer M. Nguyen, Colby College

Document Type Honors Thesis (Open Access)


The parent carbene ß-acetoxyethylidene has been previously generated by the photolysis of its precursor, acetic acid 1a,9b-dihydro-1H-cyclopropa[l]phenanthren-1-yl methyl ester. Mechanistic studies on ß-acetoxyethylidene have indicated the possibilities of three rearrangement pathways to the formation of vinyl acetate: a proton shift, an acyl shift, and a cyclic rearrangement (see Figure 8). A deuterium labeling study involving the replacement of the hydrogens on the methylene carbon has indicated that the simple 1,2-H shift was the primary manner of rearrangement, with an 82 field of product. However, a primary kinetic isotope effect may have occurred due to the greater strength of a C-D bond than a C-H bond in the 1,2-H shift. Therefore, deuterium labeling studies on the carbene center were undertaken to avoid this primary kinetic isotope effect. The monodeuterated acetic acid precursor, 1a,9b-dihydro-1Dcyclopropa[ l]phenanthren-1-yl methyl ester was generated from 1,1-dibromo-1a,9bdihydrocycloprop[ l]phenanthrene, an important carbene precursor that is produced in high yields from phenanthrene. The compound was photolyzed, and the results are forthcoming. In a second project utilizing the easily accessible 1,1-dibromo-1a,9bdihydrocycloprop[ l]phenanthrene, efforts have been made at generating a specific precursor in the generation of successive vinylidenes. Dimerization of the starting material in an effort to form the double bonded carbene precursor was attempted in a one step reaction. However, the dimerization did not fully complete, and a dibrominated dimer was formed as a product instead.