Piperitone rearrangement

In an enamine alkylation study, piperitone (8 X = H) gave, in addition to the expected dienamines, two rearranged dienamines via ring opening and reclosure hydrolysis yielded the o-menthenones (181Dauben s full paper (Vol. 7, p. 34) on... 

Interesting syntheses of racemic sativene (203), copacamphene (205), cis-sativenediol (206), and helminthosporal (207) have been reported (Scheme 32). " The key step at the start of these syntheses is the acid-catalysed thermal rearrangement of (201), which is obtained by photolysis of piperitone in 1,1-dimethoxyethane, to give the two epimeric ketones (202). These two epimers are... 

More typically, mixtures of products are formed. Terpene epoxides that have been subjected to ZnBr2-catalyzed rearrangement include the oxiranes derived from limonene, carvomenthene, other pinenes, 2,3-carvene, pulegone and piperitone. ZnCh is rarely employed, but has been compared with AICI3 in a study involving sever epoxides. In most instances there appears to be no evidence for special advantages of zinc halides compared with other more commonly used Lewis acids. 

Anionic oxy-Cope rearrangements of /ra/ts-divinylcyclohexenols also proceed with invariable E selectivity. For example, the oxy-Cope rearrangement of cyclohexenol 31 (prepared from monoterpene piperitone 30), the key step in the synthesis of medium-ring sesquiterpene ( + )-acoragermacrone, gives product 32 in a 75% overall yield935. 

Hubbs have confirmed the result obtained last year (Vol. 10, p. 29) that the piperitone photo-adduct (209) undergoes a thermal rearrangement to produce... 

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