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Issue 0, 1972
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Competitive anion formation in pulegone [p-menth-4(8)-en-3-one] synthesis of phenylmethylenepyrans

P. Crabbé,  E. Díaz,  J. Haro,  G. Pérez,  D. Salgado  and  E. Santos 

Abstract

Treatment of (+)-pulegone [p-menth-4(8)-en-3-one] with strong base generates various anions which can be quenched with benzoyl chloride. Enolization towards C-4 followed by acylation leads to p-mentha-3,8(10)-dien-3-yl benzoate (2a). 2-Benzoyl-p-mentha-2,4(8)-dien-3-yl benzoate (3) results from acylation of an enol generated at position 2. The 9,10-dianion reacts with benzoyl chloride to give a diketone, which by cyclization affords 4-benzoylmethylene-5,6,7,8-tetrahydro-7-methyl-2-phenyl-4H-chromen (6a). Compound (6a) was identified by an independent synthesis involving treatment of ethyl 4-methyl-2-oxocyclohexanecarboxylate with benzoylmethylene(triphenyl)phosphorane. In addition to 5,6,7,8-tetrahydro-7-methylflavone (9a), 2-(2,6-di-phenyl-4H-pyran-4-ylidene)-5-methylcyclohexanone (5a) and its isomer (6a) are also formed in equal yields in this reaction.

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Article type: Paper
DOI: 10.1039/P19720000046
Citation: J. Chem. Soc., Perkin Trans. 1, 1972,0, 46-49
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    Competitive anion formation in pulegone [p-menth-4(8)-en-3-one] synthesis of phenylmethylenepyrans

    P. Crabbé, E. Díaz, J. Haro, G. Pérez, D. Salgado and E. Santos, J. Chem. Soc., Perkin Trans. 1, 1972, 0, 46
    DOI: 10.1039/P19720000046

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