Among several theories proposed for the origin of homochirality, absolute asymmetric synthesis is unique because it produces chiral compounds without the intervention of any chiral factor. Here we report on the kinetically controlled heterogeneous solid-vapor phase absolute asymmetric synthesis in conjunction with asymmetric autocatalysis with amplification of chirality. Each reaction, carried out in a test tube, between achiral powder crystals of pyrimidine-5carbaldehyde and the vapor of diisopropylzinc, is controlled kinetically to afford either (S)-or (R)-pyrimidyl alkanol.Scheme 1 Absolute asymmetric synthesis initiated under (a) homogeneous and (b) heterogeneous conditions in conjunction with asymmetric autocatalysis with amplification of chirality.
Achiral inorganic gypsum (CaSO ⋅2 H O) triggers the asymmetric autocatalysis of pyrimidyl alkanol on its two-dimensional enantiotopic faces to give highly enantioenriched alkanol products with absolute configurations corresponding to the respective enantiotopic surfaces. This is the first example of highly enantioselective synthesis on the enantiotopic surface of an achiral mineral.
Achiral ethylenediamine forms chiral structures spontaneously when crystallized as the sulfate salt. By using these chiral crystals of ethylenediamine sulfate (ethylenediammonium sulfate), asymmetric autocatalysis of pyrimidyl alkanol affords a highly enantioenriched product with chirality that is determined by the chirality of the crystals.How the symmetry of molecular chirality is breaking and how enantioenriched chiral molecules are formed in achiral environments have been fundamental questions that researchers have attempted to answer to reveal the origin of biological homochirality.1 Several theories have been proposed regarding the generation of chirality through symmetry breaking, such as due to circularly polarized light 2 or spontaneous absolute asymmetric synthesis.3 One of the most widely observed symmetry-breaking phenomena is spontaneous chiral crystallization 4 of achiral compounds. However, establishing a correlation between crystal chirality and molecular chirality is challenging. We have been studying systems that display asymmetric autocatalysis, 57 whereby the enantiomeric excess (ee) of the product is amplified as the reaction progresses. Various chiral inorganic 8 and organic 9 crystals of achiral compounds can trigger asymmetric autocatalysis. In this study, we focused on chiral crystals of achiral ethylenediamine sulfate, and we achieved asymmetric autocatalysis triggered by the crystal chirality of ethylenediamine sulfate (Scheme 1).Ethylenediamine is a simple achiral diamine that is widely used as a ligand for metals in chemistry. Its sulfate salt forms chiral crystals because of the helical arrangement of molecules in the lattice structure. 10 As shown in Figure 1a, in one crystal form, all the ethylenediamine molecules adopt the gauche conformation and the nitrogen atoms are twisted clockwise when looking along the CC bond; crystals with the opposite chirality are composed of ethylenediamine molecules twisted in the counterclockwise direction. We found that such chiral crystals of ethylenediamine sulfate induce enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde to afford, in combination with asymmetric autocatalysis, 5-pyrimidyl alkanol with high enantioenrichment and with an absolute configuration that was determined by the chirality of the crystal 1.Single crystals of ethylenediamine sulfate were obtained by slow evaporation of a solution of ethylenediamine sulfate in water. After 57 days, single crystals of ethylenediamine sulfate were obtained as almost square plates (ca. 510 mm long with ca. 0.51.0 mm thickness). The existence of an optical axis in the well-developed crystal face and the strong optical rotation power of the crystals meant that the chirality of the ethylenediamine sulfate was easily determined by examining the crystal with a microscope under illumination with polarized light. Starting from an orthogonal position of the polarizing filter, (+)-crystals decreased the brightness according to clockwise rotation of the polarizer and (¹)-crystals i...
An asymmetric autocatalysis reaction was initiated by a finite single-wall carbon nanotube molecule with helical chirality. The asymmetric induction was initiated by the chiral environment arising from the planar chirality of the tubular polyaromatic hydrocarbons.
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