Diazoacetic acid esters

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). 

Other methods for the preparation of diazoacetic acid esters... 

Diazoacetic acid ester reacts with benzene and homologs to give the corresponding esters of non-caradienic acid, transformed at high temperatures to derivatives of cycloheptatriene, phenylacetic acid, and (i-phenylpropionic acid (when one or more methyl groups are present in the initial hydrocarbon). 

The most versatile carbene precursors are a-diazocarbonyl compounds such as diazoacetic acid esters because they are readily prepared, easy to handle and much more stable than ordinary diazoalkanes [10,38]. Nevertheless, one should always be aware of the potential hazards of diazo compounds in general [39],but if the necessary precautions are taken, they can be safely handled even on an industrial scale [18]. The most frequently used reagent is commercially available ethyl diazoacetate. Besides a-diazocarbonyl reagents, diazomethane [40,41 ] and a y-diazoacrylate derivative [42] have been used in enantioselective Cu-cata-lyzed cyclopropanations but the scope of these reactions has not been studied systematically. It has been shown in certain cases that diazo compounds can be replaced by other carbene precursors such as iodonium ylides, sulfonium yUdes, or lithiated sulfones [8,43],but successful applications of these reagents in enantioselective Cu-catalyzed reactions have not been reported yet. 

Carbenes and carbenoids constitute a class of reactive intermediates traditionally intimately associated with the synthesis of cyclopropanes, and more recently with products derived from C-H insertion processes. The reactions of diazoacetic acid esters with aromatic hydrocarbons such as toluene to give cyclopropanes with the liberation of N2, date back to the seminal experiments by Buchner and Curtius reported in 1885 [11]. Much later, in 1942, Meerwein reported that carbenes generated from diazomethane undergo insertion into C-H bonds [12], Seminal experiments that had significant impact for the utilization of such reactions in synthesis were performed by Stork, who demonstrated that carbenes prepared by photolysis of diazoketones participated in stereospecific intramolecular cycloadditions with al-kenes to form bicyclic cyclopropanes (Equations 1 and 2) [13]. Julia reported that intramolecular C-H insertion reactions of a chiral substrate 5 including a stereogenic methine center proceeded stereospecifically with retention of configuration (Equation 3) [14]. 

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