Michael Addition of the Trichloromethyl Anion

Electron rich enol acetates react in a fashion similar to that described above for other poor Michael acceptors. Vinyl acetate reacts in the Michael sense with chloroform under phase transfer conditions to give 2,2,2-trichloroisopropyl acetate [14,53], but more highly substituted enol acetates undergo dichlorocyclopropanation. The reaction scheme is similar to that shown in equation 2.28 (above) and the Michael addition of trichloromethide ion to vinyl acetate and the cyclopropanation of bicyclo-[3.2.1] heptanone enol acetate [54] are shown in equations 2.29 and 2.30, respectively. 

Reaction of 1,3-butadiene [55] and 1,2-butadiene [53] systems bearing electron withdrawing groups with chloroform under alkaline phase transfer conditions results in low yields of 1,1-dichlorocyclopropanes. In these systems, dichlorocarbene generally adds to the double bond most remote from the electron withdrawing substituent. Examples are shown in equations 2.31—2.33. 

E-Methyl cinnamate, E-methyl crotonate, and methyl 3-methylcrotonate are unusual in that they undergo multiple addition of dichlorocarbene when subjected to phase transfer conditions [53]. A detailed study of this reaction has resulted in evidence for an initial cyclopropanation followed by a series of dehydrochlorinations and trichloro-methyl anion additions. The resulting tetrachlorospiropentanes which result from this complex sequence are shown in equations 2.34—2.36. Note that in these cases, there is no electron releasing group on the same carbon as the Michael activating substituent. 

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