3-alkylidenephthalides synthesis

A complementary procedure for the preparation of ylidenebutenolides from maleic anhydrides, which has several advantages over the Grignard-and Perkin-type approaches, employs phosphoranylides. This approach was first applied in the synthesis of alkylidenephthalides e.g. 162) by reaction between phthalic anhydride and the appropriate triphenylphos-phorane 133). Interestingly, the condensations involving phosphoranes... 

Knight, D. W., and G. Pattenden 4-Phosphoranylidenebutenolide Intermediates in the Synthesis of 4-Ylidenebutenolides and 4-Ylidenetetronic Acids. Synthesis of Alkylidenephthalide Constituents of Celery Odour and Models for Freelingyne. J. Chem. Soc. Perkin I (London) 635 (1975). 

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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