New Thiocarbonyl Ylides Derived from 3,3‐Dichloro‐2,2,4,4‐tetramethylcyclobutanethione; Generation and Reactions.

Abstract

The reaction of 3,3-dichloro-2,2,4,4-tetramethylcyclobutanethione (1) with diazo compounds yielded spirocyclic 2,5-dihydro-1,3,4-thiadiazoles 3, which decomposed at ca. 45°C to give the corresponding thiocarbonyl ylide of type 4. In the absence of trapping agents, these thiocarbonyl ylides underwent a 1,3-dipolar electrocyclization to yield spirocyclic thiiranes 5. On the other hand, the thiocarbonyl methanide 4a was efficiently intercepted with C C, C=C, C=O, C=S, and N=N dipolarophiles leading to the [2+3] cycloadducts. A non-stereoselective cycloaddition took place when 3a was decomposed in the presence of the very electron-deficient dicyanofumarate or maleate, indicating a two step mechanism via an intermediate zwitterion. Furthermore, the thiocarbonyl methanide 4a could be trapped by the imidazole-2-thione 7 to give the 1,3-adduct 8. Treatment of 3a with secondary amines led to amidrazones of type 25 via base-catalyzed ring opening and condensation reaction.