One-step synthesis of substituted 4,7-bis[alkyl(aryl)imino]-3-oxa-6-thia-1-azaspiro[4.4]nona-1,8-dienes

Alkyl-(aryl) isocyanides react with benzoyl isothiocyanate in the presence of dialkyl acetylenedicarboxylates or dibenzoylacetylene in one-pot to afford highly substituted 4,7-bis[alkyl(aryl)imino]-2-phenyl-3-oxa-6-thia-1-azaspiro[4.4]nona-1,8-dienes, with double insertion of the isocyanide, in 38–45% yields (based on the isocyanide).