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Communication | Regular issue | Vol 104, No. 4, 2022, pp.655-666
Published online, 31st January, 2022
DOI: 10.3987/COM-21-14611
Preparation of 2,3-Dihydrobenzo[b]thiophene Bearing Benzylic Quaternary Carbon by Palladium-Catalyzed Cascade Reaction

Yosuke Hosoya, Honoka Yasukochi, Kota Mizoguchi, and Masahisa Nakada*

*Department of Chemistry and Biochemistry, School of Advanced Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan

Abstract

A palladium-catalyzed cascade reaction for preparing 2,3-dihydrobenzo[b]thiophenes and the corresponding 1,1-dioxides bearing the C3 benzylic quaternary carbon is described. This cascade reaction involves the oxidative addition of aryl iodide to Pd(0) to form a σ-aryl palladium intermediate, insertion of the internal alkene into the σ-aryl palladium intermediate to form a σ-alkyl palladium intermediate with concomitant formation of a heterocyclic ring bearing a benzylic all-carbon quaternary stereogenic center, which undergoes transmetalation with a TIPS ether of thiol, and finally, reductive elimination to afford the product. The use of N,O-bis(trimethylsilyl)acetamide (BSA) under previously optimized conditions is key to achieving a high yield.