Metal Free Sulfonylative Spirocyclization of Alkenyl and Alkynyl Amides via Insertion of Sulfur Dioxide

Abstract

Herein, we report an efficient synthesis of azaspiro[4,5]‐decanes and azaspiro[4,5]‐trienones by the radical cascade spirocyclization of N‐benzylacrylamides or N‐arylpropiolamides respectively. These reactions proceed under metal free conditions and involve in situ generation of aryl sulfonyl radicals from DABSO and aryl diazonium salts. Furthermore, a catalyst free visible light mediated protocol was developed for the sulfonylative spirocyclization of N‐aryl alkynamides using diaryliodonium salts. The utility of these protocols were justified by the excellent compatability of a wide range of functional groups, good yields and scalablity under mild conditions at room temperature.

Updates on hypervalent-iodine reagents: metal-free functionalisation of alkenes, alkynes and heterocycles

“…The title compound azaspiro[4,5]-trienones ( 71 ) were obtained in good yields from the corresponding iodonium salts (Scheme 45). 103…”

Recent Advances in the Construction of Spiro Compounds via Radical Dearomatization

“…In this approach, aryl‐substituted thiols gave 3‐sulfenyl azaspiro[4,5] trienones in moderate to good yields, whereas aliphatic thiols failed. Besides, another two groups independently developed similar protocols to prepare 3‐sulfonated azaspiro[4,5]trienones from N ‐( p ‐methoxyaryl)propiolamides 24 instead of N ‐arylpropiolamides 1 (Scheme 8c–8e) [21i,l] …”

Visible Light as the Key for the Formation of Carbon–Sulfur Bonds in Sulfones, Thioethers, and Sulfonamides: An Update

“…The reaction could be scaled up to one gram proving the robustness of the methodology. More recently, similar approaches have been applied to the preparation of azaspiro[4,5]-trienones 65 118 and to the C-H functionalization of imidazoheterocycles 124. 66 The sulfonylative spirocyclization only needed irradiation with a white LED to occur (Scheme 43D), while the derivatization of imidazoheterocycles required the Eosin Y salt as photocatalyst and irradiation with a green LED (Scheme 43E).…”