(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

Abstract

AbstractEnantiopure (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 (MαNP) and (–)‐camphorsultam dichlorophthalic (CSDP) acid methods. The diastereomeric MαNP 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.