Carbene-olefin addition

Seyferth (7) discovered that phenyl(trihalomethyl)mercury compounds decompose when heated in a solvent giving dihalocarbenes. When the solvent contains a suitable olefin, carbene addition occurs giving 1,1-dihalocyclopropane derivatives. The reaction has the advantage that strong base is not required in the reaction mixture, and base-... 

Closs, G. L., Structures of Carbenes and the Stereochemistry of Carbene Additions to Olefins, 3, 193. 

The majority of preparative methods which have been used for obtaining cyclopropane derivatives involve carbene addition to an olefinic bond. If acetylenes are used in the reaction, cyclopropenes are obtained. Heteroatom-substituted or vinyl cyclopropanes come from alkenyl bromides or enol acetates (A. de Meijere, 1979 E. J. Corey, 1975 B E. Wenkert, 1970 A). The carbenes needed for cyclopropane syntheses can be obtained in situ by a-elimination of hydrogen halides with strong bases (R. Kdster, 1971 E.J. Corey, 197JB), by copper catalyzed decomposition of diazo compounds (E. Wenkert, 1970 A S.D. Burke, 1979 N.J. Turro, 1966), or by reductive elimination of iodine from gem-diiodides (J. Nishimura, 1969 D. Wen-disch, 1971 J.M. Denis, 1972 H.E. Simmons, 1973 C. Girard, 1974). 

Relative Reactivities of Some Olefins towards Addition of Carbenes and Carbenoids in Solution... 

The dilution technique makes use of the different concentration dependence of the S—T conversion (a) and the carbene addition to the olefin (/S). The decay of the metastable singlet state is unimolecular, while the stereospecific addition rate is first-order in olefin concentration 78). The dilution technique has not yielded a common ratio in the experiments with cis- or iraws-butene and 2c (see Table 11). Extrapolation of the data to infinite dilution gives a product ratio of 0.16, suggesting that... 

R = /-Bu, MCsSi) . When the pyrolysis is carried out in the presence of olefins, the addition is non-stereospecific, signifying the presence of the triplet carbene (75). 

The cyclopropanation of alkenes with dihalocarbenes, CX2 or CX X, except for CF2, can be efficiently executed by the PTC procedures (CHX3/strong aqueous base/catalyst), which are well-documented in books and reviews . The dichloro- and dibromo-carbene additions by the PTC procedure have successfully been applied for many alkenes, conjugated polyolefins and allenes. Satisfactory results are also reported for the reactions of sterically hindered olefins as well as electronically deactivated olefins, which frequently... 

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