Completely Stereoselective Synthesis of Sulfonated 1,3-Dihydroisobenzofurans via Radical Multicomponent Reactions

Two types of new
oxidant-free radical multicomponent reactions
of β-alkynyl ketones, aryldiazonium salts, and DABCO·(SO2)2 (DABSO) were established, leading to the tunable
generation of two class of sulfonated 1,3-dihydroisobenzofurans with
moderate to good yields and complete stereoselectivity under the mild
conditions. The radical-induced scission/recombination of the C­(sp3)–C­(sp3) bond enabled direct 1,8-halosulfonylation
of β-alkynyl ketones, giving 1,3-dimethylene-substituted (1Z,3Z)-1,3-dihydroisobenzofurans
with substituent diversity by p-nitrobenzyl bromide
(PNBB) or p-nitrobenzyl chloride (PNBC) as the halo
source. Fine-tuning substituents to strong electron-withdrawing ones,
such as nitro, cyano, and trifluoromethyl, linked to aryldiazonium
tetrafluoroborates allowed a different annulation/1,5-azosulfonylation
process to access sulfonated (Z)-1,3-dihydroisobenzofurans with one quaternary carbon-amino functionality.