Pyrroles reaction with carbenes

Furan and thiophene undergo addition reactions with carbenes. Thus cyclopropane derivatives are obtained from these heterocycles on copper(I) bromide-catalyzed reaction with diazomethane and light-promoted reaction with diazoacetic acid ester (Scheme 41). The copper-catalyzed reaction of pyrrole with diazoacetic acid ester, however, gives a 2-substituted product (Scheme 42). 

Reaction of pyrrole with carbenes yields enlarged ring systems as well as 2-formylpyrrole [1003-29-8] (40). 

The Ciamician-Dennstedt reaction involves the reaction of a pyrrole (1) with the carbene generated from chloroform and a base to provide a 3-chloropyridine (2, Scheme 8.3.1). 

Fluoro-substituted dihydrofuro[3,2-r ]pyridinones are obtained from the thermolysis reaction of cyclopropa[3]-furo[2,3-f]pyrroles, 134, along with the loss of HF (Equation 67) <2005SL1006>. Compound 134 is generated from pyrroles via reaction with a carbene to give an azomethine ylide which undergoes an electrocyclization reaction. 

The ambident nucleophilic character of enaminones is again demonstrated by the reaction with keto carbenes, produced in situ from diazoketones. Acyclic enaminones react via the -position to directly yield pyrroles (equation 11). Cyclic enaminones are shown to react at the nitrogen to give adducts which can be cyclized with KOH to... 

Reaction with benzene follows a similar pathway, yielding a bicyclo[3.2.2]nonatriene structure. Vinylcarbenoids also react with pyrroles to give tropanes via a cyclopropanation-Cope rearrangement route. The direct addition of carbenes to acetylenes does not give satisfactory yields of cyclopropanes, but the rhodium carboxylate catalysed reaction of diazo compounds with acetylenes is a useful source of cyclopro-panes. Carbenoids can also attack a carbonyl oxygen atom, giving rise to a zwitterion (249). An excellent review of intramolecular carbenoid reactions has appeared. ... 

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