A new cascade halosulfonylation of 1,7-enynes toward 3,4-dihydroquinolin-2(1H)-ones via sulfonyl radical-triggered addition/6-exo-dig cyclization

Abstract

A new cascade three-component halosulfonylation of 1,7-enynes for efficient synthesis of densely functionalized 3,4-dihydroquinolin-2(1H)-ones has been established from readily accessible arylsulfonyl hydrazides and NIS (or NBS). The reaction pathway involves in situ-generated sulfonyl radical-triggered α,β-conjugated addition/6-exo-dig cyclization/radical coupling sequence, resulting in continuous multiple bond-forming events including C–S, C-C and C-I (or C-Br) bonds to rapidly build up molecular complexity.

Recent Advances in Radical‐Enabled Bicyclization and Annulation/1,n‐Bifunctionalization Reactions

“…Annulation/1,7-bifunctionalization reactionso f1,6-enynes. tion, [69] and halosulfonylation [70] of 1,7-enynes to afford av ariety of polyfunctionalized 3,4-dihydroquinolin-2(1H)-ones 170-172,r espectively (Scheme 42). Following these successful works, Li, Guo, and co-workers recently reported as elenosulfonation of N-tethered 1,7-enynes with sulfinic acids and diphenyl diselenide for the formation of multifunctional 3,4-dihydroquinolin-2(1H)-ones 173 in good-to-excellent yields under both batch andf low conditions (Scheme 43).…”

Synthesis of 3,4‐Dihydrobenzo[f]phthalazines via Iodine/tert‐Butyl Hydroperoxide‐Mediated Annulation Cascade of Yne‐Allenones

“…BHT as a radical inhibitor was used to detect the above transformation and the desired product 4 a was obtained in 45% yield (Scheme 3a). [8] These results suggested that this reaction may not include a radical mechanism and TBHP could oxidize the iodine anion to molecular iodine. Without triethylamine, the reaction of 1 p with 2 a was carried out under standard conditions, the product 4 p was isolated in 30% yield along with 28% yield of iodinated product 5 p, determined by X-ray diffraction analysis (Scheme 3b and see Supporting Information), [10] indicating that iodinated product may be an intermediate for forming final product 4.…”

“…A survey of literatures revealed that the generation of sulfonyl radicals from sulfonyl hydrazides under oxidative conditions is well established. [8] For these reasons, the reaction of yne-allenones with sulfonyl hydrazides was conducted by combining I 2 and tert-butyl hydroperoxide (TBHP) as a catalytic oxidative system. Instead of the expected cyclobuta[a] naphthalen-4-ol products 3 (Scheme 1c), the reaction proceeded in another direction to give 3,4-dihydrobenzo[f]phthalazin-6-ols 4, accompanied with naphthalen-1-ol intermediates 5.…”

Copper‐Catalyzed Sulfonyl Radical‐Enabled Regioselective Cyclization of 1,6‐Enynes

“…Specifically, readily available sulfonyl hydrazides have become general sulfonyl radical sources to install sulfonyl functional group. [5][6][7][8][9] In this context, sulfonyl hydrazides have been widely investigated as radical precursors for coupling with alkenes, [5] alkynes, [6] indoles, [7] 1,n-enynes [8] and others. [9] Recently, several groups have focused on developing sulfonyl radical-enabled cyclization of 1,n-enynes.…”