"Three-Component reaction" with aromatic thioketones, phenyl azide, and dimethyl fumarate

Abstract

The reaction of thiobenzophenone ( = diphenylmethanethione; 8a) or 9H-fluorene-9-thione (8b) and methyl fumarate (9) in excess PhN3 at 80" yields a mixture of diastereoisomeric thiiranes 10 and 11 (Scheme 1). A mechanism involving the initial formation of 1-phenyl-4,5-dihydro-1H-1,2,3-triazole-4,5-dicarboxylate 12 by 1,3-dipolar cycloaddition of PhN3 and 9 is proposed in Scheme 2.The diazo compound13, which is in equilibrium with 12, undergoes a further 1,3-dipolar cycloaddition with thioketones 8 to give 2,5-dihydro-1,3,4-thiadiazoles 14. Elimination of N2 yields the thiocarbonyl ylide 15 which cyclizes to the corresponding thiirane. Desulfurization of the thiiranes 10 and 11 with hexamethylphosphorous triamide leads to the olefinic compounds 16 (Scheme 3). The crystal structures of 10a, 11a, and 16b were determined.