Issue 23, 2022

Ligand-controlled chemoselectivity in gold-catalyzed cascade cyclization of 1,4-diene-tethered 2-alkynylbenzaldehydes

Abstract

A method to chemo- and stereoselectively assemble polycyclic bridged pyrrolidines and azepines which relies on the gold(I)-catalyzed cascade annulation of skipped 1,4-diene-tethered 2-alkynylbenzaldehydes is described. The divergence in product selectivity was accomplished by controlling the reaction pathway of the surmised Au-bound benzopyrylium species, generated from 6-endo-dig oxycyclization of the substrate, and by changing the steric nature of the ligand of the metal complex. With BrettPhosAuNTf2 (BrettPhos = dicyclohexyl(2′,4′,6′-triisopropyl-3,6-dimethoxy-[1,1′-biphenyl]-2-yl)phosphine) as the catalyst, the ensuing [3 + 2] cycloaddition/cyclopropanation cascade of the metal-bound cyclic oxonium intermediate was found to occur to afford the cyclopropane-fused bridged-pyrrolidine product. The presence of SIMesAuNTf2 (SIMes = 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene) as the catalyst, on the other hand, was observed to result in an Au-bound benzopyrylium intermediate undergoing a sequential [3 + 2] cycloaddition followed by selective C(sp3)–H bond insertion in the ensuing gold carbenoid species to give the cyclopropane-bridged-azepine ring system. The synthetic utility of the divergent catalytic protocol was demonstrated by the late-stage modification of a series of structurally complex natural products and drug molecules under mild reaction conditions.

Graphical abstract: Ligand-controlled chemoselectivity in gold-catalyzed cascade cyclization of 1,4-diene-tethered 2-alkynylbenzaldehydes

Supplementary files

Article information

Article type
Research Article
Submitted
23 Aug 2022
Accepted
03 Oct 2022
First published
04 Oct 2022

Org. Chem. Front., 2022,9, 6520-6529

Ligand-controlled chemoselectivity in gold-catalyzed cascade cyclization of 1,4-diene-tethered 2-alkynylbenzaldehydes

J. Chen, R. Hu, Q. Bao, D. Shang, L. Yu, P. W. H. Chan and W. Rao, Org. Chem. Front., 2022, 9, 6520 DOI: 10.1039/D2QO01346K

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