Menthyl propionate

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 —... 

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. 

Compound (+ )-(53) has been made from one of the diastereomers of the (—)-menthyl ester of 3-(p-anisylmethyl-l-naphthylstannyl)propionic acid, (54) ([a]p°° — 24) which could be obtained from the mixture of diastereomers because it is much less soluble in -pentane at low temperature than the other one. Their separation could be followed by NMR, both diastereomers differing by the position of their methoxy signal. The pure less soluble diastereomer (54) reacts with methylmagnesium iodide to give a tetraorganotin compound containing only one chiral center, the asymmetric tin atom 36> 87>. 

Since Barton decarboxylation can be performed under mild conditions, thermal or photolytic treatment of the Barton ester (13) of propionic acid with TV-hydroxy-2-thiopyridone in the presence of chiral menthyl acrylates generates addition products (14). However, diastereoselectivity is rather poor, since the chiral menthyl center is too far away from the C-C bond-forming position, as shown in eq. 10.7. When the chiral center is adjacent to the reaction position, stereocontrol is significantly affected, as shown in eq. 10.8 [9-12]. 

Preparative Methods the synthesis of this compound was first reported by methylation of (R)-(+)-t-Butyl 2-(p-Tolylsulfinyl)acetate via enolate generation with lithium bases such as n-Butyllithium or t-Butyllithium at 0 °C and with only lodomethane as the alkylating agent (eq 1). The diastereomeric ratio was shown by H NMR to be 50 50 with BuLi and 42 58 with t-BuLi. The title compound was also prepared from (-)-(1R,2S,5R)-Menthyl (S)-p-Toluenesulfinate and the magnesium enolate of t-butyl propionate in 68% yield as a 1 1 ratio of the two possible diastereomers (eq 2). ... 

Asymmetric Aldol Reactions. Reaction of (1) with Boron Tribromide in CH2CI2 affords, after removal of solvent and HBr, a complex (5) useful for the preparation of chiral enolates (eq 5). Complex (5) is moisture sensitive and is generally prepared immediately before use. For propionate derivatives, either syn or, less selectively, anti aldol adducts may be obtained by selection of the appropriate ester derivative and conditions. Thus reaction of f-butyl propionate with (5) and triethylamine produces the corresponding E 0) enolate, leading to formation of anti aldol adducts upon addition to an aldehyde (eq 6). Selectivities may be enhanced by substitution of the t-butyl ester with the (+)-menthyl ester. Conversely, reaction of 5-phenyl thiopropionate with (5) and Diisopropylethylamine affords the corresponding Z(0) enolates and syn aldol products (eq 7). ... 

A number of asymmetric syntheses have been developed. Aldol-type asymmetric condensations have also been effected in the naphthol series. To 1-naphthol in dichloromethane at -60°C, titanium tetrachloride was added, followed after 15 mins, stirring by menthyl pyruvate introduced over 15 mins. Quenching gave menthyl (-)2-hydroxy-2-(1-hydroxy-2-naphthyl)propionate in 81% yield (diastereoisomeric excess 92%) (ref.79). 

As one of the enzymic reactions, asymmetric synthesis catalyzed by cyclodextrins has been studied in the past, but gave all the products in a low optical yield. We have already found a strong chiral induction for the chlorination of methacrylic acid in the crystalline cyclodextrin complexes. 100 % enantiomeric excess (e.e.) of (-)-2,3-dichloro-2-methyl-propionic acid and 88 % e.e. of its enantiomer were isolated in a- and 3-cyclodextrins, respectively. This paper describes asymmetric addition of gaseous halogens and hydrogen halides in the crystalline complexes comprising trans-cinnamic acid as a reactant and a- or 3-cyclodextrin as chiral matrix. Asymmetric bromination of menthyl cinnamate and of salts from the acid and several chiral amines have been reported, but gave low chiral inductions up to 2 16 % e.e.. 

In this example, synthetic DJ.-menthol racemate is initially chemically esterified with acetate, formate, propionate, myristate, benzoate, or succinate. The ester is then selectively hydrolyzed by steriospecilic microbial enzymes to produce L-menthol that is readily isolated from the D-menthol ester. The low water solubility of the menthyl esters and L-menthol has made this process particularly suitable to non-aqueous systems. Omata et al. [90] immobilized cells of Rhodotorula minuta in photo-cross-linked or polyurethane resin gels and used a water saturated hexane eluant to obtain a product of 100% optical purity. The immobilized cells had an estimated half-life of 55 to 63 days in this solvent. 

Chiral recognition, enantioselectivity, and influence of room temperature CILs (RTIL) synthesized from 1-methyl imidazole and chloromethyl menthyl ether on excited-state photophysics of (5)-Ai-methyl-2-pyrrolidinemethyl 2(5)-(6-methoxy-2-naphthyl)propionate [(5,5)-NPX-PYR] was recently investigated using a fluorescence lifetime [114]. The chemical structures of the CILs and chiral analytes used for the lifetime study are shown in Fig. 21, left. The lifetime fluorescence decay of [(5,5)-NPX-PYR] in RTIL chiral environment is shown in Fig. 21, right. 

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