CIAMICIAN-DENNSTEDT Cyclopropanation

CIAMICIAN - DENNSTEDT Cyclopropanation Cyclopropanation of alkenes with dichlorocarbene derived Irom CHCI3 and sometimes subsequent rirtg enlargement of fused cyclopropanes 1 Na... 

CIAMICIAN - DENNSTEDT Cyclopropanation Cyciopropanation of alkenes with dichiorocarbene derived from CHCI3 and sometimes subsequent ring enlargement of fused cyclopropanes... 

The Ciamician-Dennstedt reaction can be thought of as the complement to the Reimer-Tiemann reaction (Scheme 8.3.2). The first step of both reactions is cyclopropanation of one of the carbon-carbon double bonds of a pyrrole with a dichlorocarbene, resulting in intermediate 3. The Ciamician-Dennstedt reaction results from cleavage of the internal C-C bond and elimination of chloride (path a), while the Reimer-Tiemann reaction results from cleavage of the exocyclic bond, and subsequent hydrolysis of the dichloromethyl moiety to furnish aldehyde 5 (path b). 

Ciamician-Dennstedt rearrangement. Expansion of the pyrrole ring by heating with chloroform or other halogeno compounds in the alkaline solution. The intermediate dichlorocarbene, by addition to the pyrrole, forms an unstable dihalogeno-cyclopropane that rearranges to a 3-halogenopyri-dine. 

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