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Paper | Regular issue | Vol 32, No. 6, 1991, pp.1159-1166
Published online, 1st January, 1970
DOI: 10.3987/COM-91-5713
A New Synthesis of Precocene II and Precocene III Based on the Photo-Fries Rearrangement of a Sesamol Ester

Miguel A. Miranda,* Jaime Primo, and Rosa Tormos

*ETSII, Departmento de Química, Universidad Politécnica de Valencia, Apartado 22012, E-46071 Valencia, Spain

Abstract

The photo-Fries rearrangement of the sesamol ester of 3-methylcrotonic acid (2) in the presence of potassium carbonate affords a mixture of the o-hydroxyketones (3c) and (3d). Basic cyclization of the latter leads to the chromanones (4c) or (4d), respectively. Treatment of 4c with alkoxide/alcohol results in the regioselective cleavage of the methylenedioxy ring, to give the corresponding 7-alkoxy derivatives (4e) or (4f). Subsequent methylation with methyl iodide gives rise to 4a or 4b and final reduction/dehydration by conventional methods affords the target compounds Precocene II (1a) or Precocene III (1b).