Reaction of sulfene and dichloroketene with N,N ‐disubstituted α‐aminomethyleneketones. Synthesis of 5 H ‐pyrano[3,4‐ e ]‐1,2‐oxathiin and 2 H ,5 H ‐Pyrano[4,3‐ b ]pyran derivatives

The polar 1,4‐cycloaddition of sulfene to N,N ‐disubstituted ( E )‐3‐aminomethylene‐2,3,5,6‐tetrahydro‐4 H ‐pyran‐4‐ones II, prepared from 2,3,5,6‐tetrahydro‐4 H ‐pyran‐4‐one via the 3‐hydroxymethylene derivative, occurred only in the case of aliphatic N ‐substitution to give, generally in satisfactory yield, 4‐dialkylamino‐3,4,7,8‐tetrahydro‐5 H ‐pyrano[3,4‐ e ]‐1,2‐oxathiin 2,2‐dioxides, which are derivatives of the new heterocyclic system 5 H ‐pyrano[3,4‐ e ]‐1,2‐oxathiin. The cycloaddition of dichloroketene to II occurred only in two cases of aromatic N ‐substitution to give 3,3‐dichloro‐3,4,7,8‐tetrahydro‐4‐(methylphenyl)(diphenyl)amino‐2 H ,5 H ‐pyrano[4,3‐ b ]pyran‐2‐ones IVi, l . Dehydrochlorination of IV with triethylamine was successful only in the case of IV l to give 3‐chloro‐7,8‐dihydro‐4‐diphenylamino‐2 H ,5 H ‐pyrano[4,3‐ b ]pyran‐2‐one in low yield.