Phthalides 3-alkylidenephthalides

Interestingly, electrochemical reductions of alkylidenephthalides (14), which might conceivably give radicals isomeric in the heterocyclic moiety with 13, resulted either in the addition of two electrons or in ring scission, although phthalide radicals such as 15, which is not heteroaromatic, may be prepared. ... 

Moreover, they are versatile building blocks for the synthesis of functionalized naphthalenes, anthracenes, and naphthacene natural products [8]. Recently, Rh-catalyzed C-H activation followed by nucleophilic addition to aldehydes emerged as a powerful alternative to access phthalides. In 2012, Li and coworkers developed a novel Rh(III)-catalyzed synthesis of three substituted phthalides from benzoic acids and aldehydes through carboxylate-directed ortho-C-H functionalization and subsequent intramolecular cyclization (Scheme 6.2a) [9]. In 2013, GooCen and coworkers described the straightforward synthesis of S-alkylidenephthalides from benzoic acids and aliphatic acids or anhydrides in the presence of [Rh(cod)Cl]2 and CsF (Scheme 6.2b) [10]. 

Scheme 6.2 (a) Synthesis of 3-substituted phthalides from aldehydes and aromatic acids and (b) synthesis of 3-alkylidenephthalides from benzoic acids. 

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