Acyl-transfer
catalysis is a frequently used tool to promote the
formation of carboxylic acid derivatives, which are important synthetic
precursors and target compounds in organic synthesis. However, there
have been only a few structural motifs known to efficiently catalyze
the acyl-transfer reaction. Herein, we introduce a different acyl-transfer
catalytic paradigm based on the tropolone framework. We show that
tropolonate salts, due to their strong nucleophilicity and photochemical
activity, can promote the coupling reaction between alcohols and carboxylic
acid anhydrides or chlorides to give products under thermal or blue
light photochemical conditions. Kinetic studies and density functional
theory calculations suggest interesting mechanistic insights for reactions
promoted by this acyl-transfer catalytic system.
Arylation
reaction is an important transformation in synthetic chemistry as aryl building
blocks are ubiquitous in valuable organic frameworks. Traditionally, this type
of reaction has been carried out either via biaryl coupling reactions or with
the use of reactive intermediates such as arynes or aryl radicals. Direct
electrophilic arylation reactions have been rarely reported in literature, as
the required arenium building blocks are often unstable or inaccessible. To
develop a new strategy for such transformation, we herein introduce the
development of a formal phenylation
reaction, which proceeds via an electrophilic cycloheptatrienylation with
tropylium ion, followed by an oxidative ring-contraction.
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