Synthesis of the Derivatives of 2-[(2-Ethoxy-2-oxoethyl)sulfanyl]- and 2-[(2-Ethoxy-2-oxoethyl)(methyl)amino]methylfuran-3-carboxylates and Investigation of Their Intramolecular Cyclization

Series of 5-substituted alkyl 2-[(2-ethoxy-2-oxoethyl)sulfanyl]methyl- and 2-[(2-ethoxy-2-oxoethyl)(methyl)amino]methylfuran-3-carboxylates have been synthesized and intramolecular ester condensation of these compounds has been investigated. It has been shown that sulfides, when heated with sodium foil in benzene, undergo cyclization to give sodium salts of 2-substituted ethyl 4-oxo-4,7-dihydro-5H-thiopyrano[3,4-b]furan-5-carboxylates. Upon long boiling under the same conditions, sarcosine esters form sodium salts of 2-substituted ethyl 6-methyl-4-oxo-4,5,6,7-tetrahydrofuro[2,3-с]pyridine-5-carboxylates. Salts of the derivatives of dihydrothiopyrane series exist in the carbanion form, while these of tetrahydrofuropyridine derivatives are enolates. The reactions of these salts with methyl iodide and acetyl chloride predominantly yield the products of С-alkylation and С-acylation in the former case, affording the enolates in the latter case. Influence of substituents in position 5 of the furan ring on the direction of metalation and the possibility of cyclization of (3-alkoxycarbonylfur-2-yl)methylsulfanylacetates and N-(3-alkoxycarbonylfur-2-yl)methylsarcosinates into the corresponding fused systems has been observed.