Miscellaneous Reactions of Dichlorocarbene

Reaction of diclilorocarbene with substituted benzaldehydes affords the corresponding mandelic acids. It might be supposed that this reaction does not involve dichlorocarben but rather its precursor, the trichloromethide ion. Nucleophilic addition of the trichlorc methyl anion to benzaldehyde should yield phenyl trichloromethyl carbinol. In control experiments, however, phenyl trichloromethyl carbinol was not hydrolyzed to mandelic acid under the reaction conditions. It was suggested that the reaction involves dichlorocarbene addition to the benzaldehyde carbonyl to form 2,2-dichloro-3-phenyloxirane followed by rearrangement to a-chlorophenylacetyl chloride which then is hydrolyzed as shown in equation 3.16. Mandelic, 4-methylmandelic, and 4-methoxymandelic acids were produced in 75%, 80%, and 80% yields, respectively [24]. 

Thus far, there is only one dichlorocarbene reaction with a thioether reported [25]. Dichlorocarbene reacts with the allylic sulfide to form an ylid which undergoes a facile [2, 3] sigmatropic rearrangement. The product obtained after hydrolysis and chromatography is a mixture of /3,7-unsaturated-S-phenyl esters according to equation 3.17. 

Qiloroform yields both the trichloromethyl anion and dichlorocarbene as reactive intermediates under basic phase transfer conditions. The trichloromethyl anion reacts with phenylmercuric chloride under these conditions to yield phenyl(trichloromethyl)-mercury (72%). The product is unstable, however, to the 50% aqueous sodium hydroxide solution usually used in phase transfer catalysis. When 10—15% aqueous sodium hydroxide solution was used, while maintaining the ionic strength by addition of potassium fluoride, the product survived. Reasonable yields of the mercury compound were thus obtained and the reaction was successfully extended to bromodichloromethane [yielding 64% of phenyl(bromodichloromethyl)mercury] and bromoform [yielding phenyl(tribromomethyl)mercury, 54%]. The transformation is illustrated in equation 3.18 [26]. 

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