WIMMER, Zdeněk, FLORO, A., ZAREVÚCKA, Marie, WIMMEROVÁ, Martina, SELLO, G., ORSINI, F. Insect pest control agents: Novel chiral butanoate esters (juvenogens). Bioorganic & Medicinal Chemistry. 2007, 15(18), 6037-6042. ISSN 0968-0896. E-ISSN 1464-3391

During the investigation of ester derivatives juvenogens, biochemically activated insect hormonogenic compounds) of biologically active alcohols with potential application in insect pest control, a need for availability of all existing stereoisomers of ethyl N-{2-[4-(2-butanoyloxycyclohexyl)methyl]phenoxy}ethyl carbamate occurred. They were synthesized from their chiral precursors, the corresponding stereoisomers of 2-(4-methoxybenzyl)cyclohexyl butanoate, by removing their protecting group (methyl), and by subsequent condensation of the aromatic hydroxyl moiety with ethyl N-(2-bromoethyl) carbamate. The requested enantiomers of 2-(4-methoxybenzl))cyclohexyl butanoate were obtained by a Candida antarctica lipase-mediated transesterification and chiral resolution of the respective racemic cis- and trans-isomers of 2-(4-methoxybenzyl)cyclohexanol either directly or after a subsequent chemical esterification of the chiral precursor. In this synthesis, two convenient butanoic acid activating esters, vinyl butanoate and 2,2,2-trifluoroethyl butanoate, were employed, and the chiral precursors in the synthesis of the target molecules were obtained in 41-48% yields (i.e., 82-96% conversion), and with enantiomeric purity ee = 96-98Y, respectively. The enantiomeric purity of the products was determined by chiral HPLC analysis, and their absolute configuration was assigned on the basis of analyzing & H-1 and F-19 NMR spectra of their diastereoisomeric Mosher acid (3,3,3-trifluoromethyl-2-methoxy-2-phenylpropanoic acid) esters.