Process for preparing methyl-6, alpha-ionones (alpha-irones) isomers, by the cyclization of methyl-3-pseudo-ionones

摘要

Methyl-6,a -ionones are prepared by slow addition of boron trifluoride in small molecular excess to a solution of pseudo-irones in dry benzene while cooling with a freezing mixture. The product is rich in stereoisomer having the cis (2,6) structure found in orris oil and of which the phenyl-4-semicarbazone melts at 164.5-165 DEG C. Pseudo-irones obtained by condensation of methyl-3-citrals with acetone are mixed with dry benzene, and boron fluoride introduced at 0-5 DEG C. Caustic soda is added while keeping below 10 DEG C., and the benzene layer worked up to recover the a -irones which are converted to phenyl-4-semicarbozones and fractionally crystallized. Specification 643,353 is referred to.