Catalyzed reaction of dimethyl diazomalonate with 2-mono- and 2,5-dialkyl-(alkenyl)furans

Conclusions

• 1. The catalyzed reaction of 2-substituted furans with dimethyl diazomalonate in the presence of Rh(OAc)₂ at 20°C gives the dimethyl esters of the Z-isomers of substituted 5-oxopenta-1,3-diene-1,1-dicarboxylic acids (yields up to 100%), which undergo smooth thermal rearrangement (150°C) to the E-isomers. 2,5-Disubstituted furans react to give the products of insertion of bis(methoxycarbonyl)carbene into the β-C-H bond of the furan ring, in addition to the esters of the oxodienoic acids.

• 2. Analogous reactions of 2-alkenylfurans with dimethyldiazomalonate afford both adducts of the carbene to the exocyclic double bond, and products of the reaction of the carbene with the furan ring (diesters of the oxotrienedicarboxylic acids). Introduction of methyl substituents into the β-position of the vinyl group in the starting 2-alkenylfuran modifies the course of the reaction to give predominantly (or exclusively) the oxotrienoate esters.

• 3. The reaction of 2-propenylfuran with dimethyl diazomalonate in the presence of Rh(OAc)₂ to give the 3-methyl-2-(2-furyl)cyclopropane-1,1-dicarboxylate ester has been found to be fully stereoselective.

• 4. The structures of the oxodienedicarboxylate esters formed in the reaction of furans with dimethyldiazomalonate, and of their thermal rearrangement products, have been confirmed by x-ray diffraction analysis, in the cases of the dimethyl esters of Z-7-methyl-5-oxoocta-1,3,6-triene-1,1-dicarboxylic and E-5-oxohexa-1,3-diene-1,1-dicarboxylic acids.