3.3- Dichloropropenes

Reaction of the azophosphoranes (Scheme 7.32) with dichlorocarbene follows an interesting pathway to produce l-aryl-5-chloropyrazole-3-carboxylic esters. The initial displacement of the phosphine (probably as the oxide) has been confirmed by the isolation of the 3,3-dichloropropenic ester under mild conditions. Subsequent conversion into the pyrazole appears to involve reaction with a trichloromethyl anion followed by attack by a second dichlorocarbene, although evidence for the mechanism of these steps is circumstantial [40],... 

An annulation protocol has been elaborated that uses lithiated 3,3-dichloropropene 124 generated in situ by deprotonation as a key intermediate. When added to a cycloalkanone, the homoallylic alcohol 125 forms upon aqueous workup. Its subsequent treatment with trifluoroacetic acid brings about elimination of water and dissociation of a chloride anion. 

SCHEME 16. Ring annulation of cycloalkanones due to Uthiated 3,3-dichloropropene... 

Similar products have been characterized as mutagenic following the chlorination of humic acids as a possible model for drinking water mutagens (33). These include compounds such as 3,3-dichloropropenal, dichloroacetonitrile, and l,l-dichloro-2-propanone (34). To date, however, for humic acids, only a small fraction of the mutagenesis obtained following chlorination has been accounted for by the identified compounds (33). Chian et al. (35) presented an analysis of the chemical products of humic acid chlorination in relation to those contained in residues of chlorinated water from a surface source. 

The self-condensation of 3,3-dichloropropenal and of 4,4-dichlorobut-3-en-2-one gives rise to the pyran-2-ones (331) and (332), respectively (59CI(L)992,62IZV2096). 

Acetophenones react with 3,3-dichloropropenal to give 1-aryl-5,5-dichloropenta-2,4-dienones 505 which on treatment with thiourea afford 6-aryl-2/7-thiopyran-2-thiones (Scheme 188) <2000MC77>. 

Carbenoid equivalent. Generation of gem-dichloroallyllithium (1) from 3,3-dichloropropene and lithium 2,2,6,6-tetramethyIpiperidide in the presence of an ulkene results in formation of gem-chlorovinylcyclopropanes (2) in 20-40% yield (crude). The paper also reports reduction of one of these products to a vinylcyclo-propane (3) with sodium-ammonia. ... 

Vinylcyclopropanes. Vinylcyclopropanes can be obtained in fair to moderate yields by the reaction of 1,3 or 3,3-dichloropropenes with a, 3-unsaturated esters in the presence of this complex in benzene at 80°. 

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