8-Phenylmenthol 8-Phenylmenthyl

Chiral Auxiliary for Asymmetric Induction. Numerous derivatives of (—)-8-phenylmenthol have been utilized for asymmetric induction studies. These include inter- and intramolecular Diels-Alder reactions, dihydroxylations, and intramolecular ene reactions of a,p-unsaturated 8-phenylmenthol esters. These reactions usually proceed in moderate to good yield with high diastereofacial selectivity. a-Keto esters of 8-phenylmenthol (see 8-Phenylmenthyl Pyruvate) have been used for asymmetric addition to the keto group, as well as for asymmetric [2 -F 2] photoadditions and nucleophilic alkylation. Ene reactions of a-imino esters of 8-phenylmenthol with alkenes provide a direct route to a-amino acids of high optical purity. Vinyl and butadienyl ethers of 8-phenylmenthol have been prepared and the diastereofacial selectivity of nitrone and Diels-Alder cycloadditions, respectively, have been evaluated. a-Anions of 8-phenylmenthol esters also show significant diastereofacial selectivity in aldol condensations and enantiose-lective alkene formation by reaction of achiral ketones with 8-phenylmenthyl phosphonoacetate gives de up to 90%. ... 

Hydroperoxide-n-Butyllithium gives 50% de. Chiral 3-amino esters of 8-phenylmenthol have been prepared in 50-60% de by the addition of amines to the re face of 8-phenylmenthyl crotonate under 14-15 kbar pressures (eq 2). Much higher (75 to >99%) de is obtained using 8-0-naphthyl)menthol crotonate. The 3-amino esters obtained are of the proper configuration for conversion to biologically active 3-lactams. ... 

Tin(IV) Chloride-catalyzed ene reaction of the pyruvate ester of (—)-8-phenylmenthol with 1-hexene gives a single diastereomer of the unsaturated (S)-a-hydroxy ester (de>90%) (eq 3). Similarly, tin(I V) chloride-catalyzed ene reactions of 8-phenylmenthyl glyoxylates afford unsaturated secondary alcohols with 93-98% de of the (S) configuration. ... 

Phenylmenthol is also used as a chiral auxiliary in the reduction of several xan-thatesR. Standard radical reactions with tributyltin hydride at different temperatures yield the (-)-8-phenylmenthyl esters in moderate to good diastereomeric ratios. The bulk of the a-alkyl substituent shows a small influence on the selectivity. The absolute configuration of the products are assigned only for the (—)-8-phcnylmcnthyl 2-phenylpropanoate by reduction to the corresponding alcohols. 

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