3- Menthene, epoxide

For many years the formula 559 for santolinenone has been suspect. The last nail in its coffin has finally been driven by Guella et al., who, after disposing of a certain amount of published rubbish, have synthesized 559 from 1-menthene epoxide (560), by ring opening (lithium diisopropylamide) and oxidation (silver carbonate on Celite). They carefully described 559, the corresponding alcohols, and the dimer of 559, so there is no further excuse for inadequate characterization of this pseudo-product. 

Menthol from (+)-3-Carene. An Indian manufacturing process for (—)-menthol starts from 3-carene, the major component of Indian turpentine oil (55-65%). (+)-3-Carene isomerizes to (+)-2-carene, which can be pyrolyzed to (+)-tra s-2,8-/ -menthadiene. Isomerization of the latter yields (+)-isoterpi-nolene, which is hydrogenated to give >50% (+)-3-/ -menthene. Epoxidation and subsequent rearrangement lead to a menthone isomenthone mixture,... 

The results of the dioxirane epoxidation of some 3-alkyl-substituted cyclohexenes and of 2-menthene indicate that the diastereoselectivity control is subject to the steric interactions of the dioxirane with the substituents of the substrate, while the size of the dioxirane substituents has only a minimal effect . In the favored transition structure, the alkyl groups of the dioxirane cannot interact effectively with the substituents at the stereogenic center of the chiral alkene . ... 

Alternatively, (+)-tew-isolimonene can be isomerized to (+)-2,4(8)-/>-menthadiene (34), which is partially reduced to (+)-3-menthene (35). Epoxidation of (+)-3-menthene gives the epoxide, which can be isomerized to (—)-menthone. 

Thiol synthesis. A powerful flavor-impact constituent of grapefruit juice is 1 -p-menthene-8-thiol (3). It has been synthesized by reaction of thiourea with the epoxide I to give 2 followed by reduction with LiAlH4. 

The only derivative of 1,4-cineole (554) we feel constrained to mention is not even a natural product. As a herbicide, however, Cynmethylin (622) will doubtless soon be present in the environment. It was synthesized by epoxidation of l-menthen-4-ol (547), using vanadium-catalyzed rerf-butyl hydroperoxide. 

The synthesis of l(7)-menthene-2,8-diols (655) has been mentioned (Vol. 4, p. 526, Ref. 503) the two isomers have now been isolated from Osmitopsis asteriscoidesThe known acetate 656, an insect repellent, has been isolated from Mentha haplocalyx oil, and a review of synthetic methods has been published by Verghese. In this connection, attention is drawn to a method for reducing an epoxide in the presence of a ketone, by reaction with phenyl telluride anion, PhTe, then triphenyltin hydride. The dihydrocarvone epoxides (657) yielded the hydroxy dihydroketone 658 corresponding to 656. Note also... 

Access to 3-menthene-l,8-diol (670), one of the minor products isolated (as its 1-acetate) from incubation of 7-terpenyl acetate (671) with a suspension of cultured Nicotiana tabacum cells, was conveniently achieved by reduction of piperitenone epoxide (620) with lithium aluminum hydride. ... 

Limonene (68) was biotransformed via limonene-l,2-epoxide (69) to 8-p-menthene 1,2-frani -diol (71b). On the other hand, (-i-)-carvone (93) was biotransformed via (-)-isodihydrocarvone (101b) and la-hydroxydihydrocarvone (72) to (-i-)-8-p-menthene-l,2-tran5 -diol (71a) (Noma et al., 1985a, 1985b) (Figure 14.28). A soil Pseudomonad formed 1-hydroxydihydrocarvone (72), 8-p-menthene-l,2-tra i-diol (71b) from (-i-)-limonene (68). Dhavalikar and Bhattacharyya (1966) considered that the formation of 1-hydroxy-dihydrocarvone (66) is from dihydrocarvone (64). 

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