Monoterpenes acylic

Allylation of acyloyl-imidazoles and pyrazoles61 with allyl halide mediated by indium in aqueous media provides a facile regioselective synthesis of P, y-unsaturated ketones (Scheme 11.1), which has been applied to the synthesis of the monoterpene artemesia ketone. The same product can be obtained by indium-mediated allylation of acyl cyanide (Eq. 11.35).62 Samarium, gallium, and bismuth can be used as a mediator for the allylation of nitrones and hydrazones to give homoallylic hydroxylamine and hydrazides in aqueous media in the presence of Bu4NBr (Scheme 11.2).63 The reaction with gallium and bismuth can be increased dramatically under microwave activation. 

Ali, M.S. et al., A chlorinated monoterpene ketone, acylated (J-sitosterol glycosides and a flavanone glycoside from Mentha longifolia (Lamiaceae), Phytochemistry, 59, 889, 2002. 

Ali MS, Saleem M, Ahmad W, Parvez M, Yamdagni R (2002) A Chlorinated Monoterpene Ketone, Acylated (3-Sitosterol Glycosides and a Flavanone Glycoside from Mentha longifolia (Famiaceae). Phytochemistry 59 889... 

The conversion of a bicyclo[2.2.1]octenone derivative to the corresponding bicyclo[3.3.0]octenone, a common intermediate in the total synthesis of several iridoid monoterpenes, was achieved by N.C. Chang et al. The target was obtained by sequential application of the Corey-Chaykovsky epoxidation, Demjanov rearrangement and a photochemical [1,3]-acyl shift. 

Alkenylsilane acylation has been employed for the synthesis of two furano monoterpenes, dehydroel-sholzione (1) and isoegomaketone (2 Scheme 5). Acylation of isobutene with 3-methyl-2-furoyl chloride gave dehydroelsholzione in poor yield with a variety of Lewis acid catalysts (SnCU, AlCb, TiCU), but using the equivalent silane substrate, the ketone was obtained in 55% overall yield. Probably as a result of work-up conditions, the initial reaction gave a mixture of three products, the conjugated and deconjugated ketones, together with the chloro ketone addition product. Isomerization and dehydrochlorination were effected with a tertiary amine base to maximize the yield of the desired product. 

From the fruits of Gleditsia japonica, which have been used in Japanese and Chinese folk medicine as a diuretic and expectorant, seven saponins (gleditsiasaponins B, C, Dj, D2, E, G and I) had been isolated. The structural elucidation of these saponins have been carried out by the chemical degradations, enzymatic hydrolysis and C-NMR spectra, and characterized as 3, 28-0-bisglycosides of echinocystic acid acylated with monoterpene carboxylic acid [46-49]. 

A monoterpene glycoside isolated from the fruits of Gymnocladus chinensis has been shown to contain the acylated disaccharide -0- -D-glucopyranoeyl-4-0-(2-methylbutanoyl)-et.L-arablnosyl moiety. 

The acylic monoterpenes myrcene (7-methyl-3-methylene-l,6-octadiene) and ocimenes (a-ocimene 3,7-dimefliyl-l,3,7-octatriene, alloocimene 2,6-dimethyl-2,4,6-octatriene) (Fig. la-c) represent unsaturated hydrocarbons bearing conjugated double bonds, which in principle can be polymerized by radical, anionic, and cationic procedures as well as by coordination polymerization processes. 

Chiral ketene equivalent 60 was prepared from pulegone (63), a common monoterpene. Both enantiomers of 63 are known and thus, both enantiomers of 60 are available. A model that rationalizes the observed diastereoselectivity follows. The model emphasizes three points (1) The ester reacts from a conformation that minimizes dipole-dipole repulsion in terms of conformation around the 0-acyl bond. This is normally the lowest energy conformation for any ester. (2) Steric effects are minimized in the presumed reactive complex between 60 and the Lewis acid. The metal complexes opposite the large ester alkyl group, and the vinyl dienophile reacts from an -trans conformation to minimize metal-vinyl group interactions. (3) r-Stacking contributes to shielding of one face of the olefin from the diene. It is notable that the non-catalyzed process shows little asymmetric induction. 

---