Cascade heterocyclization in the reaction of tetrafluorobenzobarrelene with 3-methoxycarbonyl-2-pyridinesulfenyl chloride

Abstract

In recent years, we have developed a new approach to the synthesis of sulfur and nitrogen containing hetero cycles based on the polar cycloaddition of hetarenesulfenyl chlorides HetSCl to alkenes, dienes, and acetylenes accompanied by the ring closure through the nitrogen atom of the HetS fragment.1—6 In particular, it was found that the reactions of 2 pyridinesulfenyl chlorides con taining substituents in the pyridine moiety even with rather readily transformable bicyclic olefins, such as norbornene3 and norbornadiene,6 afford exclusively cycloaddition products with retention of the carbon skeleton of the starting unsaturated compound. With the aim of extend ing the synthetic scope of this approach, in the present study we examined the possibility of performing the tandem rearrangement—cyclization reaction with the use of readily available tetrafluorobenzobarrelene (1)7,8 as the model substrate. The choice of diene 1 was determined by the fact that its reactions with various electrophilic reagents, including sulfenylating agents, involve cascade skeletal rearrangements.8—10