Chlorovinyl carbanions

Apart from copper(I)-mediated reactions, few studies of the treatment of vinyliodonium salts with carbanions have appeared. The vinylations of the 2-phenyl- and 2- -hexyl-l,3-indandionate ions shown in equations 222 and 223 are the only reported examples of vinyliodonium-enolate reactions known to this author26,126. ( ,)-l-Dichloroiodo-2-chloroethene has been employed with aryl- and heteroarvllithium reagents for the synthesis of symmetrical diaryliodonium salts (equation 224)149,150. These transformations are thought to occur via the sequential displacement of both chloride ions with ArLi to give diaryl (/ -chlorovinyl)iodanes which then decompose with loss of acetylene (equation 225). That aryl(/ -chlorovinyl)iodonium chlorides are viable intermediates in such reactions has been shown by the conversion of ( )-(/ chlorovinyl)phenyliodonium chloride to diaryliodonium salts with 2-naphthyl- and 2-thienyllithium (equation 226)149,150. 

A useful, although somewhat limited, method of preparing vinyl azides involves the addition of azide ion to vinyl halides with subsequent elimination of halide ion. This reaction is only possible when the halogen is located to a group which can effectively stabilize the intermediate carbanion. A number of alkyl and aryl substituted )3-chlorovinyl ketones (23) have been found to react in this way ". In many cases, however, the resulting /3-azidovinyl ketones (26) cannot... 

Alkylphosphonate esters. The carbanion generated from dechlorination with BuLi condenses with aldehydes (and some ketones). Catalytic hydrogenation of the (chlorovinyl)phosphonate products affords phosphonates. 

An aqueous NaOH-promoted intramolecular aza-Michael addition of a-carbamoyl,a-(l-chlorovinyl)ketene-S,S-acetals 25 followed by fhe nucleophilic vinylic substitution reaction furnished 1,4,4-frisubstituted 3-alkylidene-2-azetidinones 28 [37], An inframolecular aza-Michael addition of the nitrogen atom to the unsaturated p-carbon of ketene-S,S-acetals 25 under basic conditions generafes a carbanion 26, which subsequenfly rmdergoes profonation in aqueous alcoholic media to afford the intermediate products 27 (Scheme 8). Finally, the displacement of chloride in compounds 27 by alkoxide ion via nucleophilic vinylic substitution reaction leads to the formation of 2-azetidinones 28. In most of the cases, only (E)-isomer was obtained. 

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