Wolff Rearrangement of Oxidatively Generated α‐Oxo Gold Carbenes: An Effective Approach to Silylketenes

Abstract

Gold-catalyzed oxidations of alkynes by N-oxides offer a direct access to reactive α-oxo gold carbene intermediates from benign and readily available alkynes instead of hazardous diazo carbonyl compounds. Despite various versatile synthetic methods developed based on this strategy, one of the hallmarks of α-oxo carbene/carbenoid chemistry, i.e., the Wolff rearrangement, has not been realized in this context. This study discloses the first examples that the Wolff rearrangement can be readily realized by α-oxo gold carbenes oxidatively generated from TBS-terminated alkynes. The thus-generated silylketenes can be isolated pure or subsequently trapped by various internal or external nucleophiles in one pot to afford α-silylated carboxylic acids, their derivatives or TBS-substituted allenes.

Recent Progress in N-Heterocyclic Carbene Gold-Catalyzed Reactions of Alkynes Involving Oxidation/Amination/Cycloaddition

“…Only very recently, Zhang and coworkers discovered an elegant protocol for the facile and straightforward synthesis of a wealth of valuable silylketenes through NHC gold-catalyzed oxidative rearrangement of TBS (t-butyldimethylsilyl)-terminated alkynes with quinoline N-oxide [84]. It should be noted that this was the first example of the Wolff rearrangement by oxidatively generated α-oxo gold carbene species.…”

Nitrene Transfer and Carbene Transfer in Gold Catalysis

“…Wolff Rearrangement. Very recently, the first goldcatalyzed oxidative Wolff rearrangement was demonstrated by L. Zhang, Xu, and co-workers (Scheme 167) 191. In the presence ofScheme 162.…”

Non‐Diazo C−H Insertion Approach to Cyclobutanones through Oxidative Gold Catalysis

“…With the optimal conditions (Table , entry 10) secured, we then varied the phenyl group of 1 b . As shown in Table , an n ‐butyl group was tolerated (entry 1), but the substrate with a cyclohexyl group underwent mostly the Wolff rearrangement, which upon subsequent hydrolytic decarboxylation led to the formation of the ketone 5 in 79 % yield (entry 2). A cyclopropyl group, however, had little such side reaction (entry 3).…”