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. 2014 Apr 23;136(16):5844-7.
doi: 10.1021/ja500716j. Epub 2014 Apr 14.

Dual visible light photoredox and gold-catalyzed arylative ring expansion

Xing-zhong Shu  1 , Miao Zhang, Ying He, Heinz Frei, F Dean Toste
Affiliations

Dual visible light photoredox and gold-catalyzed arylative ring expansion

Xing-zhong Shu et al. J Am Chem Soc. .

Abstract

A combination of visible light photocatalysis and gold catalysis is applied to a ring expansion-oxidative arylation reaction. The reaction provides an entry into functionalized cyclic ketones from the coupling reaction of alkenyl and allenyl cycloalkanols with aryl diazonium salts. A mechanism involving generation of an electrophilic gold(III)-aryl intermediate is proposed on the basis of mechanistic studies, including time-resolved FT-IR spectroscopy.

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Figures

Scheme 1
Scheme 1. Reaction of 1a with Diazonium Compounds
Unless noted otherwise, method A was used: visible light, 1a (0.2 mmol), ArN2BF4 (3 equiv), Ph3PAuCl (10 mol%), Ru(bpy)3(PF6)2 (2.5 mol%), degassed MeOH/CH3CN (3:1, 5 mL) under N2 at rt. Method B was used: Ph3PAuCl (10 mol%), Ir(ppy)3 (2.5 mol%). Method C was used: (4-CF3Ph)3PAuCl (10 mol%), Ru(bpy)3(PF6)2 (2.5 mol%). Isolated yields are given. Yields were calculated on the basis of 1H NMR using internal standard.
Figure 1
Figure 1
Temporal behavior of intermediate (1488 cm–1) and final product (1515 cm–1) of arylation–ring expansion of vinylcyclobutanol in liquid solution monitored by rapid-scan ATR FT-IR spectroscopy. The panel on the right shows the temporal behavior on an expanded absorbance scale for clarity. The band at 1730 cm–1 is the C=O mode of the expanded ring.
Scheme 2
Scheme 2. Proposed Mechanism for Photoredox-Promoted, Gold-Catalyzed Ring Expansion–Arylation Reaction
See this image and copyright information in PMC

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