Three‐Component Reactions with Sterically Crowded 2,2,4,4‐Tetramethyl‐3‐thioxocyclobutanone, Phenyl Azide, and Electron‐Deficient C,C‐Dipolarophiles

In order to trap ‘thiocarbonyl‐aminides’ A , formed as intermediates in the reaction of thiocarbonyl compounds with phenyl azide, a mixture of 2,2,4,4‐tetramethyl‐3‐thioxocyclobutanone ( 1 ), phenyl azide, and fumarodinitrile ( 8 ) was heated to 80° until evolution of N 2 ceased. Two interception products of the ‘thiocarbonylaminide’ A (ArPh) were formed: the known 1,4,2‐dithiazolidine 3 ( cf. Scheme 1 ) and the new 1,2‐thiazolidine 12 ( Scheme 2 ). The structure of the latter was established by X‐ray crystallography ( Fig.1 ). The analogous ‘three‐component reaction’ with dimethyl fumarate ( 9 ) yielded, instead of 8 , in addition to the known interception products 3 and 6 ( Scheme 1 ), two unexpected products 15 and 16 ( Scheme 3 ), of which the structures were elucidated by X‐ray crystallography ( Fig.2 ). Their formation is rationalized by a primary [2 + 3] cycloaddition of diazo compound 18 with 1 to give 19 , followed by a cascade of further reactions ( Scheme 4 ).