Monocyclic Monoterpenoids

Cyclobutane.—Further reports of grandisol (90) synthesis include Magnus s full paper (Vol. 6, p. 22) and an almost identical Japanese report of an earlier synthesis (Vol. 3, p. 25) based upon a dihydropyranone-ethylene cycloaddition.A third synthesis utilizes cyclopropanation of 4-methoxy-3,6,6-trimethylcyclohexa-2,4-dienone to yield (91) followed by rearrangement of the a-oxycyclopropylcarbinyl cation of (91) to (92). After reduction of the cyclobutanone, second-order Beckmann cleavage of the cyclopentanone oxime gave (93) from which grandisol (90) was readily obtained. 

Cyclobutane.—Grandisol syntheses have been re viewed,and Trost s full paper on grandisol and fragranol synthesis (Vol. 6, pp. 21, 22) has been published. 

Reagents i, Nitrite ester, Av ii, A iii, ether-acetone-2 % aq. HC1 iv, Ph3P=CH2-DMSO  

Cyclopentanes.—Several new iridanes have been isolated recently theveside (74) and its methyl ester from the apocynaceous species, Thevetia peruviana (Pers.) K. Schum, and the C9 iridoid glucoside galiridoside (75) from Galeopsis tetrahit L. (labiatae). A rich source of iridoid ester glycosides is the valerian 

It has been shown that 7-deoxyloganic acid (81) is a precursor of various iridoglucosidesFeeding experiments on the plants Gardinia jasminoides and Paederia scandens have shown that the acid is incorporated into the irido-glucosides of these plants and a biogenetic scheme is proposed.  

Iridoglucosides recently isolated from the plant Gardinia jasminoides are gardenoside (82) and geniposide (83), while from the fruit, genipingentiobioside (84) has been isolated. Recently, small amounts of deacetylasperulosidic acid methyl ester (85), as well as the new iridoglucoside shanzhiside (86), have also been found in the plant.  

Inouye, S. Saito, H. Taguchi, and T. Endo, Tetrahedron Letters, 1969, 2347. 

A review by CavilP summarises the earlier literature of the simpler iridoids. From the chrysope-attracting plant Actinidia polygama several ethers have been obtained, some of which have been synthesised by two groups. The 

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Mono-COT compounds, 25 441 Monocots, fibers from, 27 18 Monocotyledonous grains, 26 267 Monocryl sutures, 24 222 Monocyclic monoterpenoid alcohols,... 

Those monocyclic monoterpenoids are characteristic mainly for various mentha oils. 

Two useful supplementary volumes " " update the corresponding chapters in the second edition of Rodd on acyclic and monocyclic monoterpenoids/ on bicyclic monoterpenoids,and on the biogenesis of mevalonate, hemiterpenoids, and monoterpenoids.A useful textbook on natural plant constituents includes some biochemistry and chemistry of monoterpenoids. ... 

Menthol (1-methyl-4-isopropylcyclohexan-3-ol) is a monocyclic monoterpenoid, which possesses three asymmetric carbon atoms and therefore exists in eight stereoisomeric forms as shown in Figure 4.23. 1-Menthol is the most highly desired of these since it produces a physiological cooling effect. That is, when applied to skin or mucus membranes, 1-menthol creates the sensation of cooling independent of the... 

Terpineol, or more strictly, a-terpineol (3.38), is one of the most widespread of monocyclic monoterpenoid alcohols in nature. It is found in flowers such as narcissus and freesia herbs such as sage, marjoram, oregano and rosemary in the leaf oil of Ti-tree Melaleuca alternifolia) and in the oil expressed from the peel of lemons. Reports of the level of terpineol in oils occasionally vary considerably and one wonders how much this is due to variations in the plants and to variations in the isolation process since terpineol could be an artefact. The layman will often describe the odour of terpineol as pine disinfectant since terpineol is, in fact a major component of pine disinfectant. This product is prepared by distillation of turpentine in the presence of acid which results in opening of the ring of a-pinene (3.37) to produce a-terpineol as shown in Figure 3.19. 

Having reviewed the principles of stereochemistry, we are now in a position to investigate the chemistry of mint. There are many species and sub-species of mint and their chemistry is dominated by monocyclic monoterpenoids, mostly alcohols and ketones. Some of the more important ones are shown in Figure 4.9. By far the most important of these are carvone and menthol, both of which will be discussed in more detail later. 

Another process of major importance is the acid catalysed hydration of a-pinene to give a-terpineol as is described in section Monocyclic Monoterpenoid Hydrocarbons under a-terpineol. 

Monocyclic Monoterpenoid Alcohols and Their Esters a-Terpineol... 

The third (and probably the least likely) route, suggested by Wolinsky et al. (1965), starts from the widely distributed monocyclic monoterpenoid limo-... 

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