8-Phenylmenthyl Crotonate

[81002-19-9]  · C20H26O2  · 8-Phenylmenthyl Crotonate  · (MW 300.46)

(chiral ester for asymmetric induction)

Alternate Name: (1R,2S,5R)-5-methyl-2-(1-methyl-1-phenylethyl)cyclohexyl crotonate.

Solubility: sol organic solvents.

Form Supplied in: not commercially available.

Preparative Methods: isolated as an oil from the esterification of (-)-8-Phenylmenthol with 2-butenoic acid (DCC, DMAP, CH2Cl2).1

Analysis of Reagent Purity: NMR2 and [a]D.

Handling, Storage, and Precautions: no special precautions are necessary other than those used for combustible organic compounds.

General Discussion.

Reaction of the crotyl ester of (-)-8-phenylmenthol with organocopper reagents in the presence of Boron Trifluoride gives good chemical yields and >99% de of the 1,4-addition product where addition has taken place from the re face (eq 1).1 Extension of this methodology to the 8-phenylmenthyl cis-butenoate gives significantly lower de.1 Epoxidation of 8-phenylmenthyl crotonate with t-Butyl Hydroperoxide-n-Butyllithium gives 50% de.2 Chiral b-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-(b-naphthyl)menthol crotonate. The b-amino esters obtained are of the proper configuration for conversion to biologically active b-lactams.3

1. (a) Oppolzer, W.; Löher, H. J. HCA 1981, 64, 2808. (b) Carpita, A.; De Magistris, E.; Rossi, R. G 1989, 119, 99.
2. Meth-Cohn, O.; Moore, C.; Taljaard, H. C. JCS(P1) 1988, 2663.
3. d'Angelo, J.; Maddaluno, J. JACS 1986, 108, 8112.

Harry E. Ensley & Yunjie Dang

Tulane University, New Orleans, LA, USA

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