Diazo compounds diazopyruvates

Acetylenedicarboxylic acid esters and related activated alkynes are routinely used as dipolarophiles for diazo dipoles. Recent examples include the use of diazo compounds 20 (49), 23 (51), and 24 (52) (Scheme 8.7), 25 (56) (Scheme 8.8), diazoacetaldehyde dimethylacetal (41) (which after cycloaddition and deprotection gave the corresponding pyrazole-3-carbaldehyde), ethyl 3-diazopyruvate (270), p-tolyl-trifluoromethyldiazomethane (271), bis(trifluoromethyl)diazomethane (272), and diazomethylenephosphoranes (60). 

Certain diazoketones, for example diazopyruvate, alkyl 2-diazo-3-oxobutyrate or 3-diazo-2,4-pentanedione, react with vinyl ethers under metal catalysis to give dihydrofurans rather than cyclopropanes l Most work on this type of transformation has been that of Wenkert and Alonsoand their respective groups. A representative example is shown in equation 107. Finally, carbenoid dimerization is also a competitive reaction in metal catalysed intermolecular cyclopropanation. However, control of the chemoselectiv-ity to favour the cyclopropanation is possible. In general, the dimeric product can be avoided by using excess of alkene or by very slow addition of the diazo compound to a mixture of alkene and catalyst... 

Without the disadvantage of using diazo compounds in the first step, Wenkert s latest monoterpenoid syntheses would be most efficient approaches, and in any case represent novel routes to well-known materials. Nezukone (754) was the result of examining the reaction between butadiene and diazopyruvic ester catalyzed by rhodium tetraacetate. The major product of the addition was the cyclopropane 758 (Scheme 62). It was known that divinylcyclopropanes could be thermolyzed to cycloheptadienes (Vol.4, p.537, Ref.600). The Wittig product from 758 thus gives a cycloheptadiene, and subsequent steps are shown in the scheme. The last step involves Grignard addition to the ester function of the enolate, then loss of water and redistribution of the double bonds.(Further examples of the use of diazo compounds will be found under perillene in the section on furans.)... 

Diazo-1,3-dicarbonyl compounds such as alkyl 2-diazo-3-oxobutyrates 57a, b and 3-diazo-2,4-pentanedione 57 c behave like the diazopyruvate 56, as far as their carbenoid cycloaddition behavior is concerned 114,130). 

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). 

Alkoxyalkenes (alkyl vinyl ethers, 8.109) form dihydrofurans with various diazocarbonyl compounds, e.g., ethyl 3-diazo-2-oxopropionate (diazopyruvate, 8.110) in the presence of copper and rhodium catalysts (see Wenkert et al., 1977,... 

---