Preparation and pyrolysis of some sulphinyl-stabilised phosphorus ylides

Abstract

The results of further investigation into the pyrolytic behaviour of alkane- and arenesulphinyl alkoxycarbonyltriphenylphosphoranes are reported. Flash vacuum pyrolysis (FVP) of these ylides at 600°C gives vinyl sulphides, sulphides and aldehydes. The vinyl sulphides and aldehydes are explained by assuming extrusion of Ph₃P=O, followed by C-H insertion in the resulting carbene to give a β-lactone. This can either lose CO₂ to give the vinyl sulphides or fragment in the opposite sense to give the aldehydes together with unknown products. The sulphides are explained by assuming extrusion of Ph3P, followed by successive loss of CO and CO₂. A variable temperature study of Ph₃P=C(CO₂Et)SOEt has revealed a complex pattern of interdependent restricted rotation of both ester and sulphinyl groups. FVP of the alkanesulphinylbenzylidenetriphenylphosphoranes at 500°C gives the alkyl thiolobenzoates by oxygen transfer in the carbene formed by extrusion of Ph3P. The first three examples of arenesulphinyl benzylidenetriphenylphosphoranes have been prepared. FVP of these at 500°C gives a mixture containing aryl thiolobenzoates formed as above together with ketones, sulphides, thiols, disulphides and stilbene. Mechanisms are suggested for the formation of these products. Four new alkyl sulphonyldiazoacetates have been prepared. FVP of these at 600°C gives vinyl sulphones, while at lower temperatures, products resulting from transfer of oxygen in the carbenes formed by extrusion of N₂ predominate.