(R)-(+)-[VCD(-)984]-4-Ethyl-4-methyloctane: A cryptochiral hydrocarbon with a quaternary chiral center. (1) synthesis of the enantiopure compound and unambiguous determination of absolute configuration

摘要

Enantiopure (R)-(+)-[VCD(-)984]-4-ethyl-4-methyloctane (1), a cryptochiral hydrocarbon with a quaternary chiral center, was synthesized by the use of 2-methoxy-2-(1-naphthyl)propionate (Mα NP) and (-)-camphorsultam dichlorophthalic (CSDP) acid methods. The diastereomeric Mα NP and CSDP acid esters prepared from racemic 2-butyl-2-methyl-1-tetralols, were effectively separated by HPLC on silica gel, and their absolute configurations were unambiguously determined by X-ray crystallographic analysis and ~1H NMR anisotropy methods. The recovered enantiopure 2-butyl-2-methyl-1-tetralol [(1S,2S)-(+)-cis-9] was then converted into the hydrocarbon (+)-1, the R absolute configuration of which was unambiguously determined for the first time. The structure of hydrocarbon 1 was also confirmed by NMR HSQC-TOCSY analysis.