Abstract
Methyl 6H-furo[2,3-b]pyrrole-5-carboxylate (2a) was prepared by thermolysis of the corresponding methyl 2-azido-3-(3-furyl)propenoate (1). 6-Methyl (2b) and 6-benzyl (2c) derivatives were obtained using phase-transfer catalysis conditions (PTC). The formylation of 2a-2c gave 2-formylated compounds (3a-3c). Compounds 4b, 4c were prepared by reactions of corresponding esters 2b, 2c with hydrazine in refluxing ethanol. By reaction of 3a-3c with hydroxylammonium chloride in acetic anhydride in the presence of pyridine, methyl 2-cyano-6-R1-furo[2,3-b]pyrrole-5-carboxylates (5a-5c) were obtained. The reaction of these compounds with sodium azide and ammonium chloride in dimethylformamide led to methyl 2-(5'-tetrazolyl)-6-R1-furo[2,3-b]pyrrole-5-carboxylates (6a-6c). A series of 5-methoxycarbonyl-6-R1-furo[2,3-b]pyrrole-2-carbaldehyde N,N-dimethylhydrazones (7a-7c) was prepared from methyl 2-formyl-6-R1-furo[2,3-b]pyrrole-5-carboxylates (3a-3c) and unsym-dimethylhydrazine. The correlation of the 13C and 15N chemical shifts with the data of the calculated (AM1) net atomic charges is discussed.
Highlights
Furo[2,3-b]pyrroles (2a-2c) and their positional isomers furo[3,2-b]pyrroles (8a-8c) belong to A,Bdiheteropentalenes, which possess differing degrees of aromaticity based upon chemical behaviour such as their ability to undergo substitution reactions with electrophilic reagents
In the past we were interested in syntheses and studies of the reactions of furo[3,2-b]pyrroles and their benzo or dibenzo derivatives [4,5,6,7,8,9]
In continuation of our programme aimed at developing efficient syntheses of fused oxygen-nitrogen-containing heterocycles, we report here the study of the synthesis of methyl furo[2,3-b]pyrrole-5-carboxylate (2a) and its utilization in synthesis
Summary
Furo[2,3-b]pyrroles (2a-2c) and their positional isomers furo[3,2-b]pyrroles (8a-8c) belong to A,Bdiheteropentalenes, which possess differing degrees of aromaticity based upon chemical behaviour such as their ability to undergo substitution reactions with electrophilic reagents.
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