Organic Letters 2003-10-30

Polyphosphoric acid trimethylsilyl ester promoted intramolecular acylation of an olefin by a carboxylic acid: convenient construction of C-18-functionalized delta14-hecogenin acetate.

Wei Li, Philip L Fuchs

Index: Org. Lett. 5(22) , 4061-4, (2003)

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Abstract

[reaction: see text]. Polyphosphoric acid trimethylsilyl ester (PPSE)-promoted intramolecular Friedel-Crafts reactions on a nonaromatic carboxylic acid system have been investigated. Studies led to the synthesis of C-18 functionalized steroidal compounds 5 and 9a-d with strict retention of the spiroketals. Isomerization of spiroketal 9e was studied.