Formal Markovnikov Hydroazolation of Alkenes via Reductive Activation of Alkylthianthrenium Salts.

Herein, we introduce a new synthetic protocol for azole alkylation. Our strategy first engages azoles using alkenylthianthrenium electrophiles to provide 1,2-azolothianthrenium salts, then selectively excises the sulfonium moiety via single electron transfer (SET). Given that alkenylthianthrenium salts can be readily accessed from alkenes, the net azole addition-hydrogenolysis sequence unlocks a versatile approach to formal Markovnikov alkene hydroazolation. Moreover, the key radical intermediate formed after reduction can be engaged in reactions beyond hydrogen atom transfer (HAT), providing access to carboazolation products that would be otherwise prohibitively difficult to prepare. Mechanistic studies into the reduction of the alkylthianthrenium electrophile implicate an unusual silyl radical attack on DMF that generates a strong SET reductant in situ under otherwise exceedingly mild conditions. Overall, this work introduces new approaches to transform alkylsulfonium building blocks and immediately expands the range of N-alkyl azole molecules that can be readily prepared and studied.