The introduction of alkylidene substituents into the 4-position of the 3,3,5,5-tetramethyl-Δ1-pyrazoline nucleus by the thioketone plus diazoalkane reaction: synthesis of tetrasubstituted episulphides and alkenes

Abstract

A wide range of 4-alkylidene-3,3,5,5-tetramethyl-Δ1-pyrazolines (2), potential precursors of unsymmetrical trimethylenemethane biradicals, can be made through the reaction of thioketone (3b) with various diazo compounds (9) or the reaction of diazo compound (3e) with thioketones. In some cases, depending on the nature of the substituents X and Y, thiadiazoline and/or episulphide intermediates can be isolated but in others the alkene is obtained directly. Reaction of the thioketone (3b) with the diazo compound (3e) gives the thiadiazoline (13) which, when heated in the solid state and then treated with trimethyl phosphite gives the unusual, highly crowded olefin (12). A byproduct of the reaction of thioketone (3b) with diazodicyanomethane is the novel azomethine imine (11).