Metal-free regioselective cascade sulfonylation–cyclization of 3-aza-1,5-enynes with sulfur dioxide and aryldiazonium tetrafluoroborates to construct 1,2-dihydropyridines

Abstract

Radical cascade cyclization of tethered alkynes has emerged as an efficient tool to construct small but complex cyclic compounds. However, it currently relies on aryl or heteroaryl-tethered alkynes to give...

Sulfonyl radical-triggered two/three-component tandem bicyclization of CN-containing 1,6-enynes under transition metal- and base-free conditions

“…7 Generally, the formation of sulfonyl radicals usually involves two pathways (Scheme 1b): one is directly generated in photocatalytic or oxidation systems from readily available building blocks such as sulfinic acids, sulfinates, sulfonyl halides, or sulfonyl hydrazides, 8 and the other is indirectly formed by the rapid insertion of SO 2 into the in situ generated carbon radical intermediates, which are usually derived from aryldiazonium tetrafluoroborates, aryl-boronic acids, cyclic ketoximes and so on. 9 Inspired by these advancements, we first presented a tert-butyl hydroperoxide (TBHP)-promoted radical tandem bicyclization of CN-containing 1,6-enynes with sulfonyl hydrazides in a transition metaland base-free system, which efficiently achieved the formation of four new bonds and two new rings in one step (Scheme 1c, route (i)). Subsequently, we achieved a novel and more practical three-component radical tandem bicyclization of CN-containing 1,6-enynes with aryldiazonium tetrafluoroborates and sodium metabisulfite (Na 2 S 2 O 5 ).…”