Ethyl diazoacetate, photolysis

Carboalkoxymethylenes, like acylmethylenes, undergo rearrangement to ketenes as well as the olefin addition and C—H insertion reactions characteristic of methylenes.<37> Thus the photolysis of ethyl diazoacetate in olefinic solvents leads to substantial yields of products, which can be rationalized in terms of a Wolff rearrangement of the carboethoxymethylene followed by cycloaddition of the resulting ethoxyketene to the olefin ... 

Diazo compounds also undergo cycloaddition with fullerenes [for reviews, see (104),(105)]. These reactions are HOMO(dipole)-LUMO(fullerene) controlled. The initial A -pyrazoline 42 can only be isolated from the reaction of diazomethane with [60]fullerene (106) (Scheme 8.12) or higher substituted derivatives of Ceo (107). Loss of N2 from the thermally labile 42 resulted in the formation of the 6,5-open 1,2-methanofullerene (43) (106). On the other hand, photolysis produced a 4 3 mixture of 43 and the 6,6-closed methanofullerene (44) (108). The three isomeric pyrazolines obtained from the reaction of [70]fullerene and diazomethane behaved analogously (109). With all other diazo compounds so far explored, no pyrazoline ring was isolated and instead the methanofullerenes were obtained directly. As a typical example, the reaction of Cgo with ethyl diazoacetate yielded a mixture of two 6,5-open diastereoisomers 45 and 46 as well as the 6,6-closed adduct 47 (110). In contrast to the parent compound 43, the ester-substituted structures 45 and 46, which are formed under kinetic control, could be thermally isomerized into 47. The fomation of multiple CPh2 adducts from the reaction of Ceo and diazodiphenylmethane was also observed (111). The mechanistic pathway that involves the extrusion of N2 from pyrazolino-fused [60]fullerenes has been investigated using theoretical methods (112). 

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... 

Addition reactions of diazoalkanes, especially diazomethane, diazopropane, diphenyl-diazomethane and ethyl diazoacetate, onto olefins, substituted with one or two electron-withdrawing groups take place very smoothly affording pyrazolines which upon heating or photolysis can give rise to the corresponding substituted cyclopropanes by elimination of nitrogen. 

The migratory aptitude of R in (11) varies widely with its structure (see Section 3.9.2.1), the shift of an alkoxy group being among the slowest. The formation of alkoxyketenes in the photolysis of alkyl diazoacetates is a fairly recent discovery. The major competing reactions of the carbene precursor are insertions into the C—H and O—H bonds of alcohols employed as solvents and ketene traps. The extent of Wolff rearrangement varies with structure ethyl diazoacetate (20-25%), phenyl diazoacetate (45-60%), and A -methyldiazoacetamide (30%). These reactions are of limited synthetic interest at present. 

Photolysis of the products formed by reaction of dialkylchloroboranes with ethyl diazoacetate leads to near quantitative yields of the homologous ethyl alkyl acetates this technique readily accommodates bulky alkyl groups (Scheme 30). 

One of the main interests in matrix ketocarbene chemistry has been the quest for oxirene (52 R = R2 = H) and its derivatives. In principle, an oxirene should lie on the energy surface linking the two a-carbonylcarbenes 51 and 53 (Scheme 9), but whether as an intermediate or as a transition state has been much debated. Photolysis of diazoacetaldehyde (51 R = R = H) and ethyl diazoacetate (51 R = H, R = COjEt) in argon matrices was the first reported attempt to observe oxirenes. Only the corresponding... 

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]. 

One approach to the rearrangement problem for carbenes has been partially solved with the use of ethyl 2-diazomalonyl esters which are not as susceptible to rearrangements as diazoacetates (Hexter and Westheimer 1971). Vaughan and Westheimer (1969) have prepared the nitrophenyl ester of ethyl 2-diazomalonate and used it to acylate the reactive serine of trypsin. Photolysis at 253 nm has yielded a glutamic acid residue which presumably arises from the insertion of the... 

When diazoester 198 was subjected to gas-phase pyrolysis and ethanol was added afterwards, a partly different result was obtained (equation 63). AUcoxyacetate 199 is again considered to result from the Wolff rearrangement, but since both ethoxy groups in 200 stem from the added alcohol, a silene cannot be the precursor. In a separate experiment, the doubly rearranged ketene 202 was isolated and shown to react quantitatively with ethanol to give 200. Also interesting is the formation of a small amount (4%) of S-lactone 201, which appears to result from 1,4-C,H insertion of the carbene. No product of an intramolecular C,H insertion could be found after photolysis of ethyl (trimethylsilyl)diazoacetate in an inert solvent ... 

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