PHOTOCHEMISTRY OF ALKYL HALIDES - VII. CYCLOPROPANATION OF ALKENES

Article abstract of DOI:10.1016/S0040-4020(01)92370-1

The previously observed cyclopropanation of alkenes by irradiation of diiodomethane (1) in their presence has been studied in more detail and found to be a synthetically useful procedure which is significantly less subject to steric effects than the traditional Simmons-Smith method.The results from photocyclopropanation of a variety of alkenes are summarized in Tables 1 and 3-4.In a number of cases the photochemical procedure afforded improved results over the Simmons-Smith method, particularly with sterically congested alkenes.Cycloalkenes showed relative rates of photocyclopropanation as a function of ring size similar to those of the Simmons-Smith method (Table 5).However, the photocyclopropanation reaction exhibited steadily increasing relative rates with increasing substitution about the double bond-in contrast with the Simmons-Smith method (Table 6), in which steric effects offset increasing nucleophilicity of the alkene with increasing substitution.The α-iodocation 2 is suggested as the methylene transfer species.In the presence of lithium bromide cation 2 was trapped to afford bromoiodomethane.