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Solutions of carbenoids 4a and 1 la were prepared by the reaction of alkyllithiums with dihalocyclopropanes 1. Carbenoid 4a had limited stability a t -80" but could be trapped by carbonation which gave 2 in low yield and by protonation which gave 4b in high yield. Bicyclobutane 5 was the major product of thermal decomposition of 4a. Carbenoid lla was more stable at -80" as evidenced by reactions with HtO, DnO, and benzophenone. Thermal decomposition of 1 la at -20' gave diene 14, presumably via dimerization of l-methoxycyclohepta-1,a-diene (16).

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HiO, B the concerted reaction are the zwitterion, which would result from stepwise decomposition of IH+ by initial loss of a proton from oxygen, and protonated maleic anhydride, which would result from initial loss of the amine from IH+.Our results would indicate that once a tetrahedral addition product of an amide has been produced, two factors will promote decomposition in the direction of amine expulsion for any compound. These are (1) removal of the hydroxylic proton and (2) protonation of the amine functionality. Other aspects of rate differences probably will be inherent to the substrate and nucleophilic catalyst. The relative sizes of kl and k-1 will d k,the case of formation of an enzyme-substrate derivative, kllk-1 can be extremely favorable and internal bases can supply the function of B. The rate of protonation of I a t the amine will probably be diffusion limited so that this feature of catalysis will not evolve as a kinetic factor for the enzyme. Rather, the apparent basicity of the amine should be increased without a t the same time increasing the strength of the C-N bond. We are currently investigating chemical means through which this may be accomplished. Abstract:The a-haloorganolithium compounds lb, 2b, and 3b were prepared from the gem-dihalocyclopropanes by stereoselective halogen-lithium exchange using methvl-or butyllithium. T,he nucleophilic properties of these carbenoids were studied by reactions with the electrophiles H+, D+, CH31, benzophenone, and halogenating agents. The chlorination (CC14) of Ib and bromination (BrCC13) of 3b provided stereoselective routes to the epimeric bromochlorocyclopropanes 3d and 6a. Factors influencing the nucleophilic reactivity of l b and 2b are discussed.