Reactions of Furo[2,3-b]pyrrole and Furo[3,2-b]pyrrole-Type Aldehydes

Abstract

The synthesis of methyl 2-formyl-6-(methoxymethyl)furo[2,3-b]pyrrole-5-carboxylate (1d) is described. The reactions of methyl 2-formylfuro[2,3-b]pyrrole-5-carboxylates 1a-1d with malononitrile afforded methyl 2-(2,2-dicyanovinyl)furo[2,3-b]pyrrole-5-carboxylates 3a-3d, with methyl cyanoacetate methyl 2-[2-cyano-2-(methoxycarbonyl)vinyl]furo[2,3-b]pyrrole-5-carboxylates 4a-4d and with 2-furylacetonitrile methyl 2-[2-cyano-2-(2-furyl)vinyl]furo[2,3-b]pyrrole-5-carboxylates 5a-5d. Compounds 1b-1d and methyl azidoacetate gave the appropriate vinylazides 6b-6d, which were used for preparation of substituted furo[2,3-b:4,5-b']dipyrroles 7b-7d. Reactivity of furo[2,3-b]pyrrole aldehydes 1a-1d and furo[3,2-b]pyrrole aldehydes 2a-2c in their reactions with 5,5-dimethylcyclohexane-1,3-dione is compared. The prepared methyl 2-[bis(4,4-dimethyl-2,6-dioxocyclohexyl)methylfuro[2,3-b]pyrrole-5-carboxylates 8a-8d and their isomers 10a-10c cyclized into substituted octahydroxanthenes 9a-9d and 11a-11c, respectively. Methyl 4-benzyl-2- [(4,4-dimethyl-2,6-dioxocyclohex-1-ylidene)methyl]furo[3,2-b]pyrrole-5-carboxylate (12) was prepared using microwave irradiations.