Menthyl carbamate

Chiral auxiliary for asymmetric radical addition and allylation. Curran, Re-bek et al.1 have prepared the chiral auxiliary 2 from 1 by manipulation of the carboxylic acid groups to provide ( )-2, enr/o-7-(2-benzoxazolyl)-l,5,7-trimethyl-3-azabicyclo[3.3.1]nonan-2-one. The racemic auxiliary is then resolved via its menthyl carbamate to provide both (R)- or (S)-2. 

Altman et al. have used the Bamberger imidazole cleavage reaction of substituted imidazoles in producing enantio-enriched vicinal di-acylamines. Specifically ring cleavage of 25 with (-)-menthyl chloroformate introduces chiral carbamate substituents on the double bond in menthyl carbamates 28 and 29. Hydrogenation of the hydrolyzed product 30 leads to preferential formation of vicinal diamide 32 over 31 in a diastereomeric ratio of 5 1. 

C. 2° can jV-dealkylale. V) chloroforniaies carbamate (- )-menthyl chloroformate ( + )-l-(9- fluorenyl)ethylchk>roformaie... 

The reactions of electrophilic animation displayed little if any stereoselectivity (Table 3.10, entries 1 to 6). The chromatographic separation of the diastereomers was generally quite difficult. The menthyl and bomyl carbamate moieties in products 99a and 99b proved to be very stable and difficult to remove, even with prolonged reflux in 6 M HC1 or concentrated HBr, and the corresponding a-hydrazino acids could not be obtained in reasonable yield. However, the isobomyl 99c analogues were readily hydrolyzed. 

Further C6o derivatives of menthol include a menthyl malonate adduct119 and a carbamate derived from l,2-epimino[60]fullerene.429 Resin acid derivatives have been prepared by Diels-Alder reaction of C6o with methyl levopi-marate, whose parent acid can be isolated from rosin.430 Finally, a derivative of a-pinene was synthesized in the context of a study on the photochemically induced addition of allyl stannanes to Cr,o, a reaction presumably proceeding via SET from the stannane to the triplet excited fullerene.431... 

Menthyl chloroformate, [17], is commercially available and has been used in several applications. For example, Seeman et al. (72) carried out the preparative chromatographic resolution of nornicotine using [17] as a CDA. The diastereomeric carbamates formed via the reaction of racemic nornicotine with [17] were separated by preparative silica gel LC, and the pure enantiomers of nornicotine were liberated by acid-catalyzed hydrolysis of the carbamates (72). Several reports have described the use of [17] in the enantiospecific determination of drug concentrations in biological fluids thus, the reagent has been used in the analysis of encainide and some of its metabolites (73), flecainide (74), and propranolol (75), and other drugs (76). 

Polymers and copolymers of vinylic carbonates and carbamates may find interesting applications as aroma and flavours releasing agents. For example, isopropenyl menthyl carbonate has been patented (Ref. 148) as an useful monomer for the manufacture of a smoking composition comprising an admixture of tobacco and a menthol-release agent. Recently, Harwood et. al (Ref. 149) have published a new preparation of enol carbonates including especially isopropenyl menthyl carbonate by selective O-acylation of ketones sodium... 

The formation of diastereomeric ureides from chloro-fomnate reagents has been used in quantitative assays and for the preparative separation of both secondary and tertiary amines. Quantitative assays for promethazine, a tertiary amine of the phenothiazine group of pharmaceuticals, have been developed. Maibaum [100] carried out a three-stage reaction in which the racemic promethazine was reacted with vinyl chloroformate and the carbamate was subsequently hydrolysed to the secondary amine. The enantiomeric ratio of the amine was then determined as the urea following reaction with a chiral isocyanate. In a later development, Witte et al. [lOI] directly derivatized the same compound with (— )-menthyl chloroformate (17) and separated the diastereomers by HPLC. (—)-Menthyl chloroformate has also been used to resolve the enantiomers of nomicotine as... 

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