<br/>Phthalides are considered to be the derivatives of 1(3H)-isobenzofuranone and have been present in a variety of biologically active plant species[1]. For instance, phthalide derivatives such as Fuscinarin can block the entry of HIV virus[2], (−)-Herbaric acid used as an antibacterial reagent[3], 3 3-Butylphthalide (NBP) used as an anti-ischemic stroke drug[4]. To date, a variety of synthetic routes have been proposed for phthalides including transition metal-catalyzed transfer hydrogenation, ketone hydroacylation, addition reaction, aldol reaction, cyclization reaction. However most of these process failed for industrial production of phthalides, due to the following reasons; (i) poor selectivity (ii) catalysts could not be reused, (iii) require harsh reaction condition, (iv) tedious work-up and (v) the cost of the catalyst (based on noble and rare-earth metals such as rhodium, iridium, platinum, gold, and ruthenium) starting materials (mostly 2-formyl benzoic acid/ester) are too high. Recently, we observed catalytic hydrogenation of phthalic anhydride to phthalide in good yield (&gt;95%, in a few gram scales) with 100% selectivity by using transition metal loaded porous heterogeneous reusable catalyst. Most importantly, switching of selectivity from phthalide to 2-methyl benzoic acid is also possible by changing the solvent of the reaction (Scheme 1). Easy synthesis, large-scale application, solvent switchable selectivity, and efficient recycling make the protocol economical and sustainable.

Selective and solvent switchable synthesis of phthalide and 2-methyl benzoic acid from phthalic anhydride

ACS Fall 2021

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