Chiral Crystal Environment Research Articles

Asymmetric Induction in Cobaloxime Complex Crystals Due to Chiral Crystal Environment

The achiral 2-cyanoethyl group of cobaloxime complexes was isomerized to the chiral 1-cyanoethyl group on exposure to a xenon lamp in the solid state. From the crystal structures and the enantiomer or diastereomer excesses of the seven cobaloxime complexes with different axial base ligands, it was found that the chirality of the produced 1-cyanoethyl group depends on the asymmetric shape of the reaction cavity for the 2-cyanoethyl group before irradiation.

Optical enrichment in chiral crystal environment of [(R,S)-1-cyanoethyl][methyl (S)-alaninate]cobaloxime complex only by photoirradiation

Optical enrichment in chiral crystal environment of [(R,S)-1-cyanoethyl][methyl (S)-alaninate]cobaloxime complex only by photoirradiation

Diastereo- and Enantioselective δ-H Abstraction in the Solid State of 1-Benzoyl-8-benzylnaphthalene – Absolute Asymmetric Synthesis Due to a Chiral Crystal Environment

Due to the matrix effect of the crystal lattice, irradiation of ketone 1 yields 2 diastereoselectively as the main product (97% de). Furthermore, the chiral crystal environment in single crystals of 1 (space group P212121) also renders the reaction enantioselective (86% ee). Both enantiomers of alcohol 2 could be produced, depending on which enantiomorphic form of the chiral crystal was irradiated. As the ketone 1 is achiral and the chiral induction is caused exclusively by physical influences, this reaction represents a further example of an absolute asymmetric synthesis.

Diastereo- and Enantioselective δ-H Abstraction in the Solid State of 1-Benzoyl-8-benzylnaphthalene – Absolute Asymmetric Synthesis Due to a Chiral Crystal Environment

Due to the matrix effect of the crystal lattice, irradiation of ketone 1 yields 2 diastereoselectively as the main product (97% de). Furthermore, the chiral crystal environment in single crystals of 1 (space group P212121) also renders the reaction enantioselective (86% ee). Both enantiomers of alcohol 2 could be produced, depending on which enantiomorphic form of the chiral crystal was irradiated. As the ketone 1 is achiral and the chiral induction is caused exclusively by physical influences, this reaction represents a further example of an absolute asymmetric synthesis.

β–α Photoisomerization of Cobaloxime Complexes in the Solid State. 6. Asymmetric Induction Due to Chiral Crystal Environment

Abstract The crystal structure of (S)-s-butylamine(2-cyanoethyl)cobaloxime was determined by X-ray analysis; the crystal is monoclinic, and the space group is C2, Z = 4 with a = 15.656(2), b = 11.699(2), c = 11.553(1) Å, β = 96.979(9)° and V = 2100.5(5) Å3. The structure was refined by a full-matrix least-squares method to the final R value of 0.052 for 1678 observed reflections. The 2-cyanoethyl group takes a perpendicular conformation to the cobaloxime plane and has disordered conformations (A, B, and C) around the Co–C bond. The occupancy factors of A, B, and C are 0.48, 0.34, and 0.18, respectively. The crystalline sample was irradiated with a xenon lamp. The (R)-1-cyanoethyl group is preferentially produced from the (S)-s-butylamine complex. The conversion rates, which were determined by HPLC analysis using the chiral stationary phase, were obtained to be 1.17 × 10−5 and 0.59 × 10−5 s−1 for the (R)- and (S)-1-cyanoethyl groups, respectively. The diastereomeric excess is 27%. Such asymmetric induction is well explained by the shape of the reaction cavity for the 2-cyanoethyl group, and is also in good agreement with a packing-energy calculation by molecular mechanics.

ChemInform Abstract: “Absolute” Asymmetric Synthesis Using the Chiral Crystal Environment: Photochemical Hydrogen Abstraction from Achiral Acyclic Monothioimides in the Solid State.

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Generation of Chirality in Crystalline-State Isomerization of Cobaloxme Complexes

Abstract The chiral compounds were obtained from the racemic compounds and from achiral compounds in chiral crystal environment in the process of photoisomerization with retention of the single crystal form. The mechanism why and how the chirality was genarated was clearly elucidated by X-ray analyses.

"Absolute" Asymmetric Synthesis Using the Chiral Crystal Environment: Photochemical Hydrogen Abstraction from Achiral Acyclic Monothioimides in the Solid State

"Absolute" Asymmetric Synthesis Using the Chiral Crystal Environment: Photochemical Hydrogen Abstraction from Achiral Acyclic Monothioimides in the Solid State

特集―分子性結晶ダイナミックス 結晶相不斉反応

The generation of asymmetry in a chiral crystal environment is very interesting in view point of the origin of life as well as organic syntheses. Two subjects are discussed; one is the asymmetric photoisomerization in chiral crystalline field and the other is a racemic-to-chiral transformation in a racemic crystal on exposure to visible light. Since the reactions proceed with retention of the single crystal form, the processes can be easily observed by X-ray analysis and the mechanism is explained on the basis of the reaction cavity which represents the void space around the reactive group in the crystal structure.

Solid-state photochemistry: absolute asymmetric oxetane synthesis from an achiral acyclic imide using the chiral crystal environment

Photolysis of chiral crystals of an achiral N-isopropyl-N-tiglylbenzoylformamide in the solid state proceeded [2+2] cycloaddition to give a chiral oxetane, 5,7-dimethyl-3-isopropyl-1-phenyl-6-oxa-3-azabicyclo[3.1.1] heptane-2,4-dione, in high chemical end optical yields