Catalyst-free synthesis of symmetrical diaryl ketones from arylstannanes and oxalyl chloride

Oxalyl chloride (1) has been known to be involved as C1 synthon for ketone synthesis,¹ as an alternative route for carbonylation with CO gas. Given the importance of ketones in pharmaceutical and industrial applications,there is a permanent interest in finding new ways for their synthesis. Based on the exceptional leaving group ability of the trialkylstannyl group in EAS, we have recently proposed efficient catalyst-free and regioselective synthesis of unsymmetrical ketones using different acyl chlorides.² Driven by these results we initiated studies on the reaction of arylstannanes with 1. Now, we describe a novel regioselective synthesis of symmetrical diaryl ketones using 1 as C1 carbonyl synthon, under catalyst-free conditions. These results are significant from the point of view of its simplicity, the wide range of synthetically³ or commercially available arylstannanes and the associated convenience in the utilization of 1 as carbonyl synthon, instead of specific acyl chlorides. All the reactions studied went, exclusively, through an ipso-substitution independently whether the directing influences of the aryl substituents and the trialkylstannyl group are either matched or mismatched. We suggest a mechanism by which 1 acts as C1 synthon on these reactions. In addition, a special work up is proposed in order to recover the trialkyltin chlorides generated. ¹ Rao, M. L. N.; Venkatesh, V.; Dasgupta, P. Tetrahedron Lett. 2010, 51, 4975-4980. ²Lo Fiego, M. J.; Silbestri, G. F.; Lockhart, M. T.; Chopa, A. B. J. Org. Chem. 2011, 76, 1707-1714. ³ Silbestri, G. F.; Lo Fiego, M. J.; Lockhart, M. T.; Chopa, A. B. J. Organometal. Chem. 2010, 695, 2578-2585.