Menthyl

Menthyl chloride and neomenthyl chloride have the structures shown One of these stereoisomers undergoes elimination on treatment with sodium ethoxide in ethanol much more readily than the other Which reacts faster menthyl chloride or neomenthyl chloride" Why" (Molecular models will help here )... 

Horn omen thyl saUcylate (homosalate), employed as a sunscreen agent, is on a Hst of 21 compounds for OTC sunscreen products, recommended by the FDA advisory review panel on OTC bum and sunburn prevention as both "safe and effective" (30). Menthyl saUcylate (6) is also a sunscreen agent. 

An increasing number of examples of ring formation through 1,5-electrocyclization of appropriate carbanions are illustrated in Scheme 27. In the last example the use of a chiral alkoxide (R = menthyl or bornyl) results in the formation of chiral indolines with optical purities ranging from 17 to 31%. 

Menthol (hRf 15) and menthyl acetate hRt 55) yielded blue chromatogram zones caryophyllene hRf 90) and caryophyllene epoxide hRf 20 — 25) appeared red-violet and thymol hRf 40 — 45) appeared brick red in color. 

Fig. 1 Schematic sketch (A) of the separation of essential oil components (ca. 500 ng of each component) and reflectance scan of the mixture (B). Menthol (1), caryophyllene epoxide (2), thymol (3), menthyl acetate (4), caryophyllene (5), mixture (G).

J -Dehydroquinolizidine reacts with the enantiomeric (—)- and (-l-)-menthyl chloroformates forming (—)- and (-l-)-menthoxycarbonyl- -dehydroquinolizidines. These can be reduced as such or in the form of their immonium salts with sodium borohydride to (—)- and (+)-l-menthoxy-carbonylquinolizidines, which give (+)- and (-)-lupinin, respectively, on reduction with lithium aluminum hydride (243). The optical yield of the asymmetric reduction is about 10%. 

A versatile synthetic route to enantiomeric ally pure Diels-Alder adducts was deduced and found dependent on the application of enantiomerically pure 5-methoxy-174a (R=Me) and 5-(l-menthyloxy)-2(5//)-furanones 174b (R = menthyl), which were expected to undergo tt-face-selective cycloaddition with dienes. The reaction was effected by heating no Lewis acid catalysts were required (Scheme 55) (88JOC1127). 

It was found that the introduction of a sulfonyl substituent considerably enhances the furanone reactivity in Diels-Alder reaction. Thus, (55)-5-(reacted with cyclopentadi-ene at room temperature in benzene with complete conversion to the adduct 212. Also, the reaction of 211 with 2,3-dimethyl-1,3-butadiene was readily performed in refluxing benzene to give the adduct213 in 98% yield (Scheme 57) (91TL7751). 

For the regioselectivity similar rules as for the ester pyrolysis do apply. With simple, alkylsubstituted amine oxides a statistical mixture of regioisomeric olefins is obtained. On the other hand with cycloalkyl amine oxides the regioselectivity is determined by the ability to pass through a planar, five-membered transition state. This has been demonstrated for the elimination reaction of menthyl dimethylamine oxide 10 and neomenthyl dimethylamine oxide 11 ... 

It will be noted that the experiments with sodium nitrate confii m the results of Charabot and Hubert, both as regards the increase in menthyl esters and the decrease in menthone in the essential oil. 

Menthol forms an acetate, menthyl acetate,. COCHj, a thick... 

Standnikow has prepared several of the esters of menthol by heating magnesium iodo-mentholate with the esters of ethyl alcohol. For example, with ethyl acetate, propionate, and benzoate the corresponding menthyl esters were obtained. These bodies have the following boiling-points —... 

Menthyl Acetate.—This ester, of the formula CHg. CO. OC, H g, is-present in oil of peppermint, its odour being an important characteristic of that oil. It can be prepared by heating menthol with acetic anhydride and sodium acetate. Its characters are as follows —... 

Menthyl Isovalerianate.—This ester, having the formula C,H,COO. 

Geranjl, linalyl, and bornyl acetates Menthyl acetate (for peppermint oil) Geranyl tiglate (for roee-geranium oil) Santalyl acetate (for sandalwood oil) Sabinyl acetate (for savin oil). ... 

In these estimations it -is necessary to calculate all the esters and all the alcohols to one formula, expressing the result, for instance, as menthyl acetate, although as a matter of fact small quantities of the corresponding propionate and butyrate may also be present, which it is impossible to estimate separately. 

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