Hydrocarbons, cryptochiral quaternary

Scheme 20 Chiral discrimination of cryptochiral quaternary hydrocarbon...

It was shown that the asymmetric autocatalysis of chiral pyrimidyl alkanol is the only possible method to discriminate cryptochiral quaternary saturated hydrocarbons, whose chirality is not capable of determination by any current... 

Discrimination of Cryptochirality in a Saturated Quaternary Hydrocarbon by Asymmetric Autocatalysis... 

An example of a compound whose chiral discrimination poses the utmost difficulty is a saturated quaternary hydrocarbon bearing similar substituents on the asymmetric carbon atom, with a representative example being 5-ethyl-5-propylundecane,i.e., (n-butyl)ethyl(n-hexyl)(n-propyl)methane (Fig. 8) [ 106]. The enantiomer of this hydrocarbon exhibits practically no optical rotation ( of < 0.001) between 280 and 580 nm. The compound is a chiral, but to all intents an optically inactive, compound. To the best of our knowledge, the chirality of this compound has not been discriminated using any current method. Mislow called such hidden chirality cryptochirality [ 14,107]. 

Alcohol 43 (entry 31) is a starting material for the synthesis of (R)-(+)-[VCD( )984]-4-ethyl-4-methyloctane 51, a cryptochiral saturated hydrocarbon with a quaternary chirality center, as will be discussed in section 55.3.4 (see Figure 55.26). Enantiopure alcohol (l/ ,2/ )-(—)-43 was obtained by the CSDP acid method, and its AC was unambiguously determined by X-ray crystallography." However, the MaNP acid method is better than the CSDP acid method in this case because of more effective HPLC separation of diastereomeric esters (see the result in section 55.3.4). 

Fujita T, Obata K, Kuwahara S, Nakahashi A, Monde K, Decatur J, Harada N. (R)-(-l-)-[VCD(—)984]-4-Ethyl-4-meth-yloctane, a cryptochiral hydrocarbon with a quaternary chirality center. (1) Synthesis of enantiopure compound and unambiguous determination of absolute configuration. Eur. J. Org. Chem. 2010 6372-6384. 

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