Reactions with ketocarbenes

With a few recent exceptions the reactions in this group have been with the a-ketocarbenes, CH COOMe, CH COOEt, and CH-COCHs, derived from the corresponding diazo compounds. Sorm and coworkers have reported the ring-opening of furan and methylfurans upon reaction with diazoacetone decomposed by copper, via attack at... 

The ketocarbene 4 that is generated by loss of Na from the a-diazo ketone, and that has an electron-sextet, rearranges to the more stable ketene 2 by a nucleophilic 1,2-shift of substituent R. The ketene thus formed corresponds to the isocyanate product of the related Curtius reaction. The ketene can further react with nucleophilic agents, that add to the C=0-double bond. For example by reaction with water a carboxylic acid 3 is formed, while from reaction with an alcohol R -OH an ester 5 is obtained directly. The reaction with ammonia or an amine R -NHa leads to formation of a carboxylic amide 6 or 7 ... 

Insertion of a ketocarbene moiety into a C—O bond of orthoesters is normally performed with catalysis by BF3 Et20. Copper(II) trifiouromethanesulfonate was found to be a similarly efficient catalyst also, at least in some cases, whereas Rh2(OAc)4 was much less suited to promote this transformation l60). Besides the C/O insertion product 343, the alcohol insertion product 344 and, in reactions with ethyl diazoacetate, the formal carbene dimers were obtained. In agreement with BF3 EtzO, Cu(OTf)2 did not bring about insertion into a C—O bond of trimethyl... 

In this review an attempt is made to discuss all the important interactions of highly reactive divalent carbon derivatives (carbenes, methylenes) and heterocyclic compounds and the accompanying molecular rearrangements. The most widely studied reactions have been those of dihalocarbenes, particularly dichlorocarbene, and the a-ketocarbenes obtained by photolytic or copper-catalyzed decomposition of diazo compounds such as diazoacetic ester or diazoacetone. The reactions of diazomethane with heterocyclic compounds have already been reviewed in this series. ... 

The diazo ketone 3, when treated with silver oxide as catalyst, decomposes into ketocarbene 5 and dinitrogen Na. This decomposition reaction can also be achieved by heating or by irradiation with uv-light. The ketocarbene undergoes a Wolff rearrangement to give a ketene 6 ... 

An a-diazo ketone 1 can decompose to give a ketocarbene, which further reacts by migration of a group R to yield a ketene 2. Reaction of ketene 2 with water results in formation of a carboxylic acid 3. The Woljf re arrangement is one step of the Arndt-Eistert reaction. Decomposition of diazo ketone 1 can be accomplished thermally, photochemically or catalytically as catalyst amorphous silver oxide is commonly used ... 

Tsuda and Oikawa (1989) investigated the photolysis of the 1,2-isomer of 10.89 (1,2-benzoquinone diazide) by means of MINDO/3 molecular orbital calculations with configurational interaction. These authors came to the conclusion that no ketocarbene of the type of 10.90 is formed, but that the rearrangement into the cyclopentadienyl ketene 10.94 is a concerted reaction in which the elimination of nitrogen and the rearrangement take place simultaneously. In the opinion of the present author the theoretical result for 1,2-quinone diazide is not necessarily in contradiction to the experimental investigations of Sander, Yankelevich et al., and Nakamura et al., as the reagents used were not exactly the same. 

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