Base and a Substituted Halogenomethane

Method using Base and a Substituted Halogenomethane. The influence of catalyst anions (as their tetrabutylammonium salts) and cations (as chlorides or bromides) on the generation of dichlorocarbene from chloroform-sodium hydroxide has been studied under standard conditions by determining the yield of dichloronorcarane produced from the addition of the carbene to cyclohexene. The presence of olefin appears to be necessary since in its absence only very slow decomposition of the trichloromethyl anion occurs. Dehmlow has also devised a new procedure for phase-transfer-catalysed cyclopropanation. Treatment of an alkene (or cycloalkene) with sodium trichloroacetate and a tetra-alkylammonium salt in chloroform without 

In the presence of more conventional bases carbene production is supressed. The decomposition of the chlorodifluoromethyl anion has been shown to be reversible and the yield of difluorocyclopropane is increased by increasing the alkene concentration. Epoxides upon treatment with dichlorocarbene afford cyclopropanes stereospecific-ally. The reaction proceeds by stereospecific deoxygenation of the epoxide to give olefin (41) which is subsequently trapped by the carbene. 

The most significant advance in the synthesis of cyclopropanes during the course of this Report has come from the work of Olofson and co-workers. By employing the arpoon base, lithium 2,2,6,6-tetramethylpiperidide (LiTMP) the stringent selectivity requirements for proton abstraction in chloromethyl esters and ethers are 

The enantioselective addition of dichlorocarbene to unsymmetrical olefins in the presence of a chiral phase-transfer catalyst has been further examined and it has been found that the optical rotation of the product is strongly dependent on the structure of the catalyst employed. The first products of di-iodocarbene (generated from iodoform with t-butoxide) addition have been characterized and di-iodonorcarane is stable for long periods at 0 °C, contrary to earlier reports. The base-catalysed decomposition of ethyl trichloroacetate in methanol results in dimethoxycarbene formation and. 

Kimura, Y. Ogaki, K. Isagawa, and Y. Otsuji, Chem. Letters, 1976, 1149. 

The olefinic selectivity of dibromocarbene generated from bromoform has been reinvestigated and, by employing 3-ethyl-3-heptoxide as the base (to suppress alkene formation), the results reveal minimal kinetically effective carbenoid involvement. This same group of workers have shown that MeSCCl is a free carbene while PhCF is in fact a carbenoid when generated by oxygenated base. A careful study of the relative reactivity of the vinylcarbene (48) by addition to a series of para-substituted styrenes has revealed a Hammett correlation with p = —0.75 treatment of the vinyl triflate with potassium t-butoxide results in the free carbene.  

The cyclohexadienylidene (49) has been generated for the first time, and adds to olefins effectively addition to an alkyne has not been reported. 

The rates of addition of dichlorocarbene to (50)—(52) exhibit very little dependance 

The additions of dichlorocarbenes to allenes have been reported, and Dehmlow 

The use of a phase-transfer catalyst-aqueous sodium hydroxide system has now been employed in the synthesis of thiophenylcyclopropanes [e.g. (67)] from chloro-methyl phenyl sulphide. In like manner, the addition of chlorofluorocarbene to olefins works well in a two-phase system and has the advantage that olefins with base- 

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