Methyl diazoacetate, photolysis

Photolysis of diazomethane in carbon-tetrachloride in the presence of benzophenone yields 1,1,1,2-tetrachloroethane showing an enhanced absorption due to the triplet carbene. The direct photolysis of diazomethane proceeds via singlet methylene CIDNP-studies of the photolysis of methyl-diazoacetate, for which a radical pair mechanism was suggested, were recently challenged 2). 

Carbenes, such as that formed by the photolysis of methyl diazoacetate, may add to one of the carbon-carbon bonds (Scheme 6.28). 

Even poorer selectivity was observed with carboalkoxycarbenes. Thus, treatment of (62) with the carbene (63 R = H, R = C02Me) (derived by photolysis of methyl diazoacetate) gave the corresponding disilacyclopentane (M R = H, R = C02Me) in 14% yield and the disilacyclobutanes derived from insertion into primary and secondary CH bonds in 53% and 33% yield, respectively... 

In the photolysis of several cyclic ketones the recent observation of CIDNP in 13C Fourier-transform n.m.r. is taken as good evidence for the involvement of biradical species in the reactions.426 Other reactions studied with n.m.r. CIDNP techniques include the photolysis of some simple alkanones,487 some decarboxylation reactions,428 in dyestuffs,429 in electron-transfer reactions in aromatic ketones,430 in methyl diazoacetate,431 and in acylsilane432 and cleavage of... 

Photolysis of methyl diazoacetate in benzene gives all four isomers of methoxy-carbonylcycloheptatriene, of which only one reacts with maleic anhydride at room temperature, giving (302). Details have appeared of the addition of methyl coumalate (303) to butadienes to give (304) and (305). The readily accessible pyran (306) adds stereospecifically to cyclopentadiene at room temperature and to butadienes at 120 °C to give synthetically useful adducts (307) and (308). ... 

The formation of cyclopropane derivatives by photolysis of diazoalkanes in the presence of alkenes is believed to occur by photolytic decomposition of the diazoalkane to yield the carbene, followed by addition of this carbene to the alkene. Cycloaddition of this type has been reported in furan, dihydrofuran, and thiophene.198 Thus, photolysis of ethyl diazoacetate in thiophene yields the bicyclic sulfur heterocycle (215). Alternatively, photolysis of 3-diazo-l-methyl-oxindole (216) in cyclohexene leads to the formation of two isomers which are thought to have the spirocyclopropyl structure (217) photolysis in ethanol yields 3-ethoxy-1-methyloxindole.194... 

Carbenes 100, generated by UV irradiation of methyl (alkoxysilyl)diazoacetates 99, furnish l-oxa-2-silacyclopentanes 101 by 1,5-C,H insertion (equation 25)60. In order to suppress competing reaction pathways of the carbene intermediate (e.g. formation of a ketazine with excess diazo compound), the photolysis was carried out at high dilution, but, even then, yields were rather modest. Carbene insertion at CH2 seems to occur much more easily than at CH3 a preference of 3 0.6 1 for methylene insertion can be calculated from the isolated yields after correction for the number of C—H bonds. It should be noted that for both carbenes, 96 and 100, C,H insertion occurs only in the 1,5 mode whereas no 1,3-, 1,4- or 1,6-C,H insertion products could be detected. 

In contrast to the carbene and carbenoid chemistry of simple diazoacetic esters, that of a-silyl-a-diazoacetic esters has not yet been developed systematically [1]. Irradiation of ethyl diazo(trimethylsilyl)acetate in an alcohol affords products derived from 0-H insertion of the carbene intermediate, Wolff rearrangement, and carbene- silene rearrangement [2]. In contrast, photolysis of ethyl diazo(pentamethyldisilanyl)acetate in an inert solvent yields exclusively a ketene derived from a carbene->silene->ketene rearrangement [3], Photochemically generated ethoxycarbonyltrimethyl-silylcarbene cyclopropanates alkenes and undergoes insertion into aliphatic C-H bonds [4]. Copper-catalyzed and photochemically induced cyclopropenation of an alkyne with methyl diazo(trimethylsilyl)acetate has also been reported [5]. 

Cyclopropyl aldehydes.2 The reagent is a more reactive 1,3-dipole than alkyl diazoacetates. It reacts with various olefins such as styrene, methyl acrylate, and 2 to form pyrazolines a, which on photolysis are converted into the cyclopropyl acetals b. The free aldehydes (3) are obtained by acid hydrolysis in overall yields greater than 80%. 

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