Diazo compounds ketocarbenes from

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... 

Ketocarbenes (1) are usually generated from the corresponding diazo compounds (3).s Other sources which are occasionally used are a,a-dibromo compounds (4),9 sulfur ylides (5)10 and iodonium ylides (6 Scheme 2).11 The thermal or photochemical decomposition of diazo compounds in the presence of ir-systems is often complicated by indiscriminate side reactions, such as Wolff rearrangements,12 C—H insertions and hydride migrations. To avoid such problems, the use of metal-catalyzed decomposition of diazo compounds is generally preferred.1 2... 

The iodonium salt 193 derived from methyl acetoacetate behaves as an a-ketocarbene equivalent and adds to methyl ketones to give the dioxoles 194. Similar addition to C=S occurs for thioketones to give 195 and with CS2 to give the oxathiole-2-thione 196 (Scheme 18) <2002TL5997>. The corresponding diazo compound 197 reacts with succin-imide and a rhodium catalyst to give the spiro dioxole 198 <2006TL2643>. 

In the reaction of ketene with diazomethane, cyclopropanone is initially formed, which reacts with another equivalent of diazomethane to give cyclobutanone ". Diazoketones react with ketenes by addition to the diazo compound. The cycloadduct eliminates nitrogen to produce butenolides. However, the ketocarbene 370, generated from... 

The reaction, formally speaking a [3 + 2] cycloaddition between the aldehyde and a ketocarbene, resembles the dihydrofuran formation from 57 a or similar a-diazoketones and alkenes (see Sect. 2.3.1). For that reaction type, 2-diazo-l,3-dicarbonyl compounds and ethyl diazopyruvate 56 were found to be suited equally well. This similarity pertains also to the reactivity towards carbonyl functions 1,3-dioxole-4-carboxylates are also obtained by copper chelate catalyzed decomposition of 56 in the presence of aliphatic and aromatic aldehydes as well as enolizable ketones 276). No such products were reported for the catalyzed decomposition of ethyl diazoacetate in the presence of the same ketones 271,272). The reasons for the different reactivity of ethoxycarbonylcarbene and a-ketocarbenes (or the respective metal carbenes) have only been speculated upon so far 276). 

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