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Reagent-free intramolecular hydrofunctionalization: a regioselective 6-endo-dig cyclization of o-alkynoylphenols†
Chanhyun Jung,Siyuan Li,Kwanghee Lee,Mayavan Viji,Heesoon Lee,Soonsil Hyun,Kiho Lee,Young Kee Kang,Chhabi Lal Chaudhary,Jae-Kyung Jung
Green Chemistry Pub Date : 02/16/2022 00:00:00 , DOI:10.1039/D1GC04848A
Abstract

Solvent-directed intramolecular hydrofunctionalization of readily available o-alkynoylphenols 1 was successfully achieved under reagent-free conditions. The hydrofunctionalization of 1 occurred by nucleophilic attack on the phenolic oxygen followed by consecutive migration of the phenolic H atom to the alkyne center, eventually affording γ-benzopyranones 2. The phenol O–H group forms intramolecular H-bonds with the carbonyl group, and we predict that these H-bonds can be distorted into their most preferred conformation in the presence of polar solvents. A regioselective 6-endo-dig cyclization seems to be thermodynamically favoured over 5-exo-dig cyclization, as supported by DFT calculations. This strategy is remarkable because it is reagent-free, regioselective, highly atom economical, and highly atom, carbon and reaction mass efficient.

Graphical abstract: Reagent-free intramolecular hydrofunctionalization: a regioselective 6-endo-dig cyclization of o-alkynoylphenols
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