Asymmetric Autocatalysis Induced by Chiral Crystals of Achiral Tetraphenylethylenes

Abstract

The achiral hydrocarbon tetraphenylethylene crystallizes in enantiomorphous forms (chiral space group: P2(1)) to afford right- and left-handed hemihedral crystals, which can be recognized by solid-state circular dichroism spectroscopic analysis. Chiral organic crystals of tetraphenylethylene mediated enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde to give, in conjunction with asymmetric autocatalysis with amplification of chirality, almost enantiomerically pure (S)- and (R)-5-pyrimidyl alkanols whose absolute configurations were controlled efficiently by the crystalline chirality of the tetraphenylethylene substrate. Tetrakis(p-chlorophenyl)ethylene and tetrakis(p-bromophenyl)ethylene also show chirality in the crystalline state, which can also act as a chiral substrate and induce enantioselectivity of diisopropylzinc addition to pyrimidine-5-carbaldehyde in asymmetric autocatalysis to give enantiomerically enriched 5-pyrimidyl alkanols with the absolute configuration correlated with that of the chiral crystals. Highly enantioselective synthesis has been achieved using chiral crystals composed of achiral hydrocarbons, tetraphenylethylenes, as chiral inducers. This chemical system enables significant amplification of the amount of chirality using spontaneously formed chiral crystals of achiral organic compounds as the seed for the chirality of asymmetric autocatalysis.

Asymmetric Autocatalysis as a Link Between Crystal Chirality and Highly Enantioenriched Organic Compounds

“…In addition, chiral crystals composed of achiral Nbenzoylglycine, [44] 2-thenoylglycine, [45] cocrystals composed of two achiral compounds, [46] benzil, [47] tetraphenylethylene, [48] ethylenediammonium sulfate, [49] benzenecarboxylate, [50] and 2,6-di-tert-butyl-p-cresol (BHT) [51] are found to be chiral triggers of asymmetric autocatalysis (Scheme 6).…”

Role of Asymmetric Autocatalysis in the Elucidation of Origins of Homochirality of Organic Compounds

“…Enantiomorphous crystals formed from achiral N-benzoylglycine (hippuric acid) [96], 2-thenoylglycine [97], certain chiral cocrystals consisting of two achiral compounds [98], benzil [99], tetraphenylethylene [100], ethylenediammonium sulfate [101], aromatic triester [102], and 2,6-di-tert-butyl-p-cresol (BHT) [103] serve as chiral initiators of asymmetric autocatalysis (Scheme 7). It should be added that a chiral crystal composed of a racemic serine initiates asymmetric autocatalysis.…”

Asymmetric autocatalysis. Chiral symmetry breaking and the origins of homochirality of organic molecules

“…It was also found that enantiomorphous crystals composed of achiral N -benzoylglycine, 84) N -(2-thienylcarbonyl)glycine, 85) cocrystal of tryptamine and p -chlorobenzoic acid, 86) benzil, 87) tetraphenylethylene, 88) ethylenediamine sulfate, 89) benzene triester 90) and 2,6-di- t -butyl- p -cresol (BHT) 91) act as chiral triggers for asymmetric autocatalysis of 1c . Thus, asymmetric autocatalysis could serve as a macroscopic observation tool of molecular-level information on the structure of crystal surfaces.…”