Direct irradiation of a series of α,α-dichlorocyclobutanones in benzene solutions results in photocycloelimination to give 1,1-dichloroalkenes in yields ranging from 30-65%. The α,α-dichlorocyclobutanones were formed in good yields from the [2+2] cycloaddition of the terminal olefins with dichloroketene. This two-step sequence formally represents a "metathesis" of two olefinic functions and provides an easy access to functionalized 1,1-dichloroalkenes. Irradiation of the dichlorocyclobutanones in the solid state led to poor yields of 1,1-dichloroalkenes and polymeric mixtures, however, photoreactions performed in zeolites gave similar yields as those run in benzene solutions.Key words: dichlorocyclobutanones, dichloroalkenes, olefin metathesis, photocycloelimination.
A general method for the preparation of cyclopropanes is reported. Triplet-photosensitized reactions of a series of cyclobutanones give cyclopropanes as the major product. Part 1 describes the synthesis of substituted cyclobutanones used in this study. In Part 2, the photo-reactions of cyclobutanones are reported. Triplet-sensitized reactions of cyclobutanones using acetone as a sensitizer give cyclopropanes as the major non-polar products. The extent of photodecarbonylation seems to be dependent on α-substitution. Electron-donating groups promote decarbonylation while electron-withdrawing groups favour cycloelimination.Key words: photodecarbonylation, cyclobutanones, cyclopropanes, triplet-sensitization.