C. Balo, F. Fernández, X. García‐Mera
Dec 1, 2000
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Organic Preparations and Procedures International
Abstract
Methyl 6-(6-methoxy-2-naphthyl)-6-oxohexanoate (3) exhibits anti-inflammatory properties,' and has been used both as a fluorescent probe? and as an intermediate in the synthesis of other fluorescent molecules used for the study of the polarity of lipid bilayers in biological membranes.3 The synthesis of this useful molecule in moderate yields (40%) by a Friedel-Crafts reaction has been reported recently." The present work was undertaken in an attempt to improve the synthesis of 3 by reaction of a weakly ionic naphthalene organocadmium derivative with methyl adipoyi chloride (methyl 6-chlorod-oxohexanoate, 1) in the hope that addition would occur selectively at the most electrophilic carbonyl group. The reaction of an excess of the cadmium reagent of 2 with 1 gave, in addition to 6.6dimethoxy-2,2'-binaphthyl (4%) and adipic acid (lo%), the desired product 3 and a yellow solid 4, whose structure was established as described below. Compound 4 showed a highly deshielded D,O-exchangeable signal at 6 14.73 in its 'H NMR spectrum and reacted with diazomethane to afford a derivative 6, with an additional signal for a methoxy group at 6 3.60. However, neither the IR spectrum of 4 nor that of 6 were compatihle with these compounds being an acid and its methyl ester respectively. In fact, an authentic sample of 6-(6methoxy-2-naphthyl)-oxohexanoic acid (71, obtained by saponification of 3, had IR and 'H NMR spectra very different from those of 4. A close inspection of their spectroscopic data led us to assign the structures of 2-[hydroxy(6-methoxy-2-naphthyl)methylene]cyclopentanone to 4 and that of its methyl ether to 6.