Achiral 2-pyridone and 4-aminopyridine act as chiral inducers of asymmetric autocatalysis with amplification of enantiomeric excess via the formation of chiral crystals

Enantiomorphous crystals of achiral 2-pyridone and 4-aminopyridine served as sources of chirality, to induce the asymmetric autocatalysis of 5-pyrimidyl alkanol during the asymmetric addition of diisopropylzinc to the corresponding pyrimidine-5-carbaldehyde, that is, the Soai reaction. Following a significant amplification of enantiomeric excess through asymmetric autocatalysis, highly enantioenriched 5-pyrimidyl alkanol could be synthesized with their corresponding absolute configurations to those of chiral crystals of 2-pyridone and 4-aminopyridine.

Asymmetric Autocatalysis as an Efficient Link Between the Origin of Homochirality and Highly Enantioenriched Compounds

Biological homochirality of essential components such as L-amino acids and D-sugars is prerequisite for the emergence, evolution and the maintenance of life. Implication of biological homochirality is described. Considerable interest has been focused on the origin and the process leading to the homochirality. Asymmetric autocatalysis with amplification of enantiomeric excess (ee), i.e., the Soai reaction, is capable to link the low ee induced by the proposed origins of chirality such as circularly polarized light and high ee of the organic compound. Absolute asymmetric synthesis without the intervention of any chiral factor was achieved in the Soai reaction.

Circular dichroism spectroscopy of catalyst preequilibrium in asymmetric autocatalysis of pyrimidyl alkanol

Mechanistic understanding of the asymmetric autocatalysis of pyrimidyl alkanol is a highly attractive and challenging topic due to its unique feature of amplification of enantiomeric excess. Circular dichroism spectroscopic analysis of this reaction allows monitoring of the structual changes of possible catalyst precursors in the solution state and shows characteristic temperature and solvent dependence. TD-DFT calculations suggest that these spectral changes are induced by a dimer-tetramer equilibrium of zinc alkoxides.

Asymmetric autocatalysis triggered by triglycine sulfate with switchable chirality by altering the direction of the applied electric field

Triglycine sulfate (TGS) acts as a chiral trigger for asymmetric autocatalysis with amplification of enantiomeric excess, i.e., the Soai reaction. Therefore, molecular chirality of highly enantioenriched organic compounds is controlled by a ferroelectric crystal TGS, whose polarization is altered by an electric field.

Achiral amino acid glycine acts as an origin of homochirality in asymmetric autocatalysis

Achiral glycine acts as the origin of chirality in conjunction with asymmetric autocatalysis to afford highly enantioenriched compound.

Formation of enantioenriched alkanol with stochastic distribution of enantiomers in the absolute asymmetric synthesis under heterogeneous solid–vapor phase conditions

Absolute asymmetric synthesis under heterogeneous solid–vapor phase conditions in conjunction with asymmetric autocatalysis was achieved.

Reversal of the sense of enantioselectivity between 1- and 2-aza[6]helicenes used as chiral inducers of asymmetric autocatalysis

Reversal of the sense of enantioselectivity was observed between 1-aza[6]helicene 2 and 2-aza[6]helicene 3 employed as chiral inducers of asymmetric autocatalysis of pyrimidyl alkanol. In the presence of (P)-(+)-1-aza[6]helicene 2, the reaction of pyrimidine-5-carbaldehyde 1 with diisopropylzinc afforded, in conjunction with asymmetric autocatalysis, (S)-pyrimidyl alkanol 4 with high ee. Surprisingly, the reaction in the presence of (P)-(+)-2-aza[6]helicene 3 gave the opposite enantiomer of (R)-alkanol 4 with high ee. In the same manner, (M)-(-)-2 and (M)-(-)-3 afforded (R)- and (S)-alkanol 4, respectively. The sense of enantioselectivity is controlled not only by the helicity of the azahelicene derivatives but also by the position of the nitrogen atom.

Can the analyte-triggered asymmetric autocatalytic Soai reaction serve as a universal analytical tool for measuring enantiopurity and assigning absolute configuration?

An investigation is reported on the use of the autocatalytic enantioselective Soai reaction, known to be influenced by the presence of a wide variety of chiral materials, as a generic tool for measuring the enantiopurity and absolute configuration of any substance. Good generality for the reaction across a small group of test analytes was observed, consistent with literature reports suggesting a diversity of compound types that can influence the stereochemical outcome of this reaction. Some trends in the absolute sense of stereochemical enrichment were noted, suggesting the possible utility of the approach for assigning absolute configuration to unknown compounds, by analogy to closely related species with known outcomes. Considerable variation was observed in the triggering strength of different enantiopure materials, an undesirable characteristic when dealing with mixtures containing minor impurities with strong triggering strength in the presence of major components with weak triggering strength. A strong tendency of the reaction toward an 'all or none' type of behavior makes the reaction most sensitive for detecting enantioenrichment close to zero. Consequently, the ability to discern modest from excellent enantioselectivity was relatively poor. While these properties limit the ability to obtain precise enantiopurity measurements in a simple single addition experiment, prospects may exist for more complex experimental setups that may potentially offer improved performance.

Point-to-Point Ultra-Remote Asymmetric Control with Flexible Linker

An ultra-remote intramolecular (point-to-point) asymmetric control through 38 bonds (1,39-asymmetric induction) has been achieved by using the principle of direct supramolecular orientation of catalytic and reactive moieties in asymmetric autocatalysis. We found the highly stereoselective diisopropylzinc addition reaction using designed molecules possessing pyrimidine sites at each terminal of a conformationally flexible simple methylene chain.

Unusual reversal of enantioselectivity in the asymmetric autocatalysis of pyrimidyl alkanol triggered by chiral aromatic alkanols and amines

Temperature dependent inversion of enantioselectivity was observed in the asymmetric autocatalysis reaction when triggered by a wide scope of chiral alcohols and amines.

Asymmetric Induction by a Nitrogen 14 N/15 N Isotopomer in Conjunction with Asymmetric Autocatalysis

Chirality arising from isotope substitution, especially with atoms heavier than the hydrogen isotopes, is usually not considered a source of chirality in a chemical reaction. An N² ,N² ,N³ ,N³ -tetramethyl-2,3-butanediamine containing nitrogen (¹⁴ N/¹⁵ N) isotope chirality was synthesized and it was revealed that this isotopically chiral diamine compound acts as a chiral initiator for asymmetric autocatalysis.

Crystal Structure of the Isopropylzinc Alkoxide of Pyrimidyl Alkanol: Mechanistic Insights for Asymmetric Autocatalysis with Amplification of Enantiomeric Excess

Asymmetric amplification during self-replication is a key feature that is used to explain the origin of homochirality. Asymmetric autocatalysis of pyrimidyl alkanol in the asymmetric addition of diisopropylzinc to pyrimidine-5-carbaldehyde is a unique example of this phenomenon. Crystallization of zinc alkoxides of this 5-pyrimidyl alkanol and single-crystal X-ray diffraction analysis of the alkoxide crystals reveal the existence of tetramer or higher oligomer structures in this asymmetric autocatalytic system.

Helical mesoporous silica as an inorganic heterogeneous chiral trigger for asymmetric autocatalysis with amplification of enantiomeric excess

P and M-Helical mesoporous silica was found to act as a chiral inorganic trigger for asymmetric autocatalysis to afford (S) and (R)-pyrimidyl alkanol with up to >99.5% ee, respectively.

Asymmetric induction by retgersite, nickel sulfate hexahydrate, in conjunction with asymmetric autocatalysis

A chiral crystal of retgersite, nickel sulfate hexahydrate, acts as a chiral initiator of asymmetric autocatalysis, affording highly enantiomerically enriched pyrimidyl alkanols.

Asymmetric autocatalysis of pyrimidyl alkanol and its application to the study on the origin of homochirality

CONSPECTUS: Amplification of enantiomeric excess (ee) is a key feature for the chemical evolution of biological homochirality from the origin of chirality. We describe the amplification of ee in the asymmetric autocatalysis of 5-pyrimidyl alkanols in the reaction between diisopropylzinc (i-Pr2Zn) and pyrimidine-5-carbaldehydes. During the reaction, an extremely low ee (ca. 0.00005% ee) can be amplified to >99.5% ee, and therefore, the initial slightly major enantiomer is automultiplied by a factor of ca. 630000, while the initial slightly minor enantiomer is automultiplied by a factor of less than 1000. In addition, pyrimidyl alkanols with various substituents at the 2-position of the pyrimidine ring, 3-quinolyl alkanol, 5-carbamoyl-3-pyridyl alkanol, and large multifunctionalized pyrimidyl alkanols also act as highly efficient asymmetric autocatalysts in the addition of i-Pr2Zn to the corresponding aldehydes. The asymmetric autocatalysis of pyrimidyl alkanol can discriminate the chirality of various compounds. Chiral substances such as alcohols, amino acids, hydrocarbons, metal complexes, and heterogeneous chiral materials can act as chiral triggers for asymmetric autocatalysis to afford pyrimidyl alkanols with the corresponding absolute configuration of the initiator. This recognition ability of chiral compounds is extremely high, and chiral discrimination of a cryptochiral quaternary saturated hydrocarbon was established by applying asymmetric autocatalysis. By using the large amplification effect of the asymmetric autocatalysis, we can link various proposed origins of chirality with highly enantioenriched organic compounds in conjunction with asymmetric autocatalysis. Thus, a statistical fluctuation in ee of racemic compounds can be amplified to high ee by using asymmetric autocatalysis. Enantiomeric imbalance induced by irradiation of circularly polarized light can affect the enantioselectivity of asymmetric autocatalysis. The asymmetric autocatalysis was also triggered by the morphology of inorganic chiral crystals such as quartz, sodium chlorate, and cinnabar. Chiral organic crystals of achiral compounds also act as chiral initiators, and during the study of a crystal of cytosine, enantioselective chiral crystal phase transformation of the cytosine crystal was achieved by removal of the water of crystallization in an achiral monohydrate crystal. Enantioselective C-C bond formation was realized on the surfaces of achiral single crystals based on the oriented prochirality of achiral aldehydes. Furthermore, asymmetric autocatalysis of pyrimidyl alkanols is a highly sensitive reaction that can recognize and amplify the significantly small effect of a chiral compound arising solely from isotope substitution of hydrogen, carbon, and oxygen (D/H, (13)C/(12)C, and (18)O/(16)O). These examples show that asymmetric autocatalysis with an amplification of chirality is a powerful tool for correlating the origin of chirality with highly enantioenriched organic compounds. Asymmetric autocatalysis using two β-amino alcohols reveals a reversal of enantioselectivity in the addition of i-Pr2Zn to aldehyde and is one approach toward understanding the mechanism of asymmetric dialkylzinc addition, where heteroaggregates act as the catalytic species.

Self-replication and amplification of enantiomeric excess of chiral multifunctionalized large molecules by asymmetric autocatalysis

Self-replication of large chiral molecular architectures is one of the great challenges and interests in synthetic, systems, and prebiotic chemistry. Described herein is a new chemical system in which large chiral multifunctionalized molecules possess asymmetric autocatalytic self-replicating and self-improving abilities, that is, improvement of their enantioenrichment in addition to the diastereomeric ratio. The large chiral multifunctionalized molecules catalyze the production of themselves with the same structure, including the chirality of newly formed asymmetric carbon atoms, in the reaction of the corresponding achiral aldehydes and reagent. The chirality of the large multifunctionalized molecules controlled the enantioselectivity of the reaction in a highly selective manner to construct multiple asymmetric stereogenic centers in a single reaction.

Asymmetric autocatalysis triggered by oxygen isotopically chiral glycerin

Chiral (S)- and (R)-(18)O-glycerin induces enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde, and the subsequent asymmetric autocatalysis affords (R)- and (S)-pyrimidyl alkanol with high enantiomeric excess, respectively.

Asymmetric autocatalysis: triggered by chiral isotopomer arising from oxygen isotope substitution

Trigger happy: chiral oxygen isotopomers of hydrobenzoin ([(18)O](R)-1 and [(18)O](S)-1) acted as chiral triggers to induce the enantioselective addition of iPr(2)Zn to pyrimidine-5-carbaldehyde. An extremely small chiral influence arising from the presence of the oxygen isotope ((18)O) is amplified through asymmetric autocatalysis to enantioenrich the 5-pyrimidyl alkanol product.

Spontaneous absolute asymmetric synthesis promoted by achiral amines in conjunction with asymmetric autocatalysis

The origin of homochirality of organic compounds such as L-amino acids and D-sugars have intrigued many scientists, and several hypotheses regarding its homochirality have been proposed. According to the statistical theory, small fluctuations in the ratio of the two enantiomers are present in a racemic mixture obtained from the reaction of achiral molecules.

We report herein the reaction of pyrimidine-5-carbaldehyde and diisopropylzinc in the presence of achiral amine such as N,N'-dimethylpiperazine, N,N'-diethylpiperazine or N-methylmorpholine but in the absence of a chiral substance. The stochastic formation of (S)- and (R)-pyrimidyl alkanols with detectable ee was observed. This study shows that the slight fluctuation of the enantiomeric ratio of pyrimidyl alkanol produced at the initial reaction step can be enhanced significantly in conjunction with asymmetric autocatalysis with amplification of enantiomeric excess. We believe that the stochastic behavior in the formation of pyrimidyl alkanol constitutes one of the conditions necessary for spontaneous absolute asymmetric synthesis.