Reaction with diazoacetates

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). 

A shorter method has been used to prepare indolizine-1-acetic acid (88) by reaction with diazoacetic ester followed by base hydrolysis and acidification.139... 

Although C—H insertion reactions rarely occur in intermolecular reactions with diazoacetates, these are common side reactions with diazomalonates3132 (equation 10) and diazo ketones (with a-allyl vinyl ethers).33 Several mechanistic pathways are available to generate the products of an apparent direct C—H insertion reaction and these include dipolar intermediates, ir-allyl complexes and ring opening of cyclopropanes.1 Oxidative problems due to the presence of oxygen are common with copper catalysts, but these are rarely encountered with rhodium catalysts except in systems where the carbenoid is ineffectively captured.34... 

Selective O-alkylation of 2-pyridones is effected by reaction with diazoacetic esters in the presence of 2 mol% Rh2(OCOCF3)4 <20000L1641>. The reaction proceeds by selective transfer of the carbene from rhodium-carbene... 

Some examples of diazoacetic esters bearing functionalized ester groups are given in Table 12. For intramolecular cyclopropanation reactions with diazoacetic esters derived from unsaturated alcohols see Section 1.2.1.2.4.2.6.3.4. 

Other reactions of oxetanes reported include the asymmetric ring expansion of 2-substituted oxetanes in an enantioselectively catalysed reaction with diazoacetic esters to give 2,3-disubstituted tetrahydrofiirans <01T262I>, and the Lewis acid promoted reactions of 2-methoxy-2-siloxyoxetane with allylsilane <00MI651 >. 

Benzo[b]oxepine carbojcylates 21 (structurally related to 18) have been synthesized from chromones 19 by sequential cyclopropanation/ring-enlargement reaction with diazoacetate in the presence of Tms-OTf/Cu(OTf)2 (Tms = trimethylsilyl) [9], for example ... 

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