Zinc Oxide: a new tool for the solvent free regioselective C-arylsulfonation of Indoles

TOCCO, GRAZIELLA;BEGALA, MICHELA

2011-01-01

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Abstract

trans-Resveratrol is a natural phenolic component of Vitis vinifera L. (Vitaceae). It has shown a number of biological activities, including protection against coronary heart disease, as a result of different effects: significant antioxidant activity, modulation of lipoprotein metabolism, vasodilatatory and platelet antiaggregatory properties. Recently we have reported the synthesis of a series of resveratrolo-coumarine hybrids that showed interesting vasorelaxant and platelet antiaggregatory activities [1,2]. In an attempt to prepare more active heterocyclic derivatives which incorporate the nucleus of the resveratrol, we synthesised a new series of 2-arylbenzofurane derivatives by an intramolecular Wittig reaction starting from the appropriate triphenylphosphonium salt and the corresponding aroyl chloride. The desired Wittig reagent was readily prepared from the conveniently substituted 2-hydroxy-benzyl alcohol and triphenylphosphine hydrobromide (Figure 1) [3]. However, while developing our methodology, we observed, together with the desired 2-arylbenzofurane derivatives with the general stricture 1, the formation of the side products 2 in a ratio ranging from 2:1 to 8:1. To get insight on the structure and on the mechanism of formation of these side reaction products, we decided to undertake a mass spectrometric study using an ion trap mass spectrometer operating under both EI and CI conditions. In particularly, MS/MS experiments were performed on the molecular ions and on the diagnostic fragment ions generated by the side products 2 as well as by the side product synthesised from labelled starting aroyl chloride. The data so obtained were consistent with the aroyl-benzofurane structure, a scaffold of many pharmaceutical drug candidates [4], thus allowing us to discover and develop a new and convenient approach to the preparation of this class of active compounds.