2-Diazo-5,5-dimethylcyclohexane-l,3-dion

Dimethyl-2-phenylspiro[2.5]nonane-4,8-dione (17) was obtained with high enantioselectiv-ity from styrene and 2-diazo-5,5-dimethylcyclohexane-l,3-dione (diazodimedone) in the presence of a copper complex bearing chiral 1,3-dioxo ligands derived from 3-trifluoroacetyl-( + )-camphor. The catalysts retain their activity even if linked to a polymeric support. Despite the impressive optical induction for this transformation, no other successful applications of these catalysts have so far been reported with a trisubstituted alkene, only very low enan-tioselectivity was observed. ... 

The carbenoid reaction between a-diazo ketones and simple alkenes or styrenes leads to acylcyclopropanes. (For the enantioselective cyclopropanation of styrene with 2-diazo-5,5-dimethylcyclohexane-l,3-dione, see Section 1.2.1.2.4.2.6.3.2.). With ketene acetals, 2,3-dihyd-rofurans are obtained. In contrast, l-acyl-2-oxycyclopropanes or 2-oxy-2,3-dihydrofurans can be formed in reactions with enol ethers and enol acetates the result depends strongly on the substitution pattern of both reaction partners.Whereas simple diazo ketones usually lead to cyclopropanes (Table 15), 3-diazo-2-oxopropanoates and 2-diazo-l,3-dicarbonyl compounds, such as 2-diazoacetoacetates, 3-diazopentane-2,4-dione, and 2-diazo-5,5-dimethylcy-clohexane-1,3-dione, yield 2,3-dihydrofurans and occasionally acyclic structural isomers thereof when reacted with these electron-rich oxy-substituted alkenes. 

Diazo-5,5-dimethylcyclohexan-l,3-dione (140) with an excess of acrylate esters serving as both reactant and solvent in the presence of rhodium acetate afforded benzofuran 141 (98SC865). The formation of the dihydrofurans probably proceeded via a 1,3-dipolar cycloaddition of a metal carbenoid to the x,/)-unsa titrated ester (98SC865). Similarly, the reaction can take place with dihydrofuran, furan, and 1-acetyl indole to give 109,142, and 143, respectively (91JOC6269) (Scheme 24). 

Azido)(chloromethylidene)dimethylammonium chloride (2.156), as a diazotransfer reagent, is comparable to the benzothiazolazidinium salt 2.144. The former also reacts in neutral or acidic solution (Kokel and Viehe, 1980). The yield of 2-diazo-5,5-dimethylcyclohexane-l,3-dione (2.121, 78-80%) is comparable to that with the benzthiazolazidinium ion 2.144 (Balli et al., 1978 a). ... 

A similar example with a relatively electrophilic diazoalkane is the diazo transfer (2-66) from ethyl diazonitroacetate (2.164) to 5,5-dimethylcyclohexane-l,3-dione (2.120) described by Schdllkopf et al. (1969). 

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