Rui Tamura

Ideal enantiomeric resolution by recrystallization of a racemic compound (part 4): Relationship between enantiomeric resolution phenomenon and crystal properties

A new example of a racemate showing unusual enantiomeric resolution phenomenon, in which simple recrystallization of the racemate leads to remarkable enantiomeric enrichment of either enantiomer up to 100% ee in the mother liquor, has been found. This compound is (±)-[2-[4-(3-ethoxy-2-hydroxypropoxy)phenylcarbamoyl]-ethyl]dimethylsulfonium p-nitrobenzenesulfonate [EtOCH2CH(OH)CH2OC6H4NHCOCH2CH2SMe2+O2NC6H4SO3−] [(±)-SN]. By repeating recrystallization of (±)-SN and the resulting deposited crystals successively and collecting the resulting enantiomerically enriched mother liquors with the same chirality sense, highly efficient enantiomeric resolution of the racemate into its separate enantiomers has been accomplished. The relationship between the occurrence of this enantiomeric resolution phenomenon and the crystal properties has been investigated with respect to SN and its aryl- and alkylsulfonate derivatives. The mode of enantiomeric resolution of (±)-SN was similar to that of para-substituted benzenesulfonate derivatives (±)-ST (4-MeC6H4SO3−) and (±)-SC (4-ClC6H4SO3−) previously reported, whereas the unsubstituted derivative (±)-SB (C6H5SO3−) and alkysulfonate derivatives (±)-SO (n-C8H17SO3−) and (±)-SM (CH3SO3−) did not show such an enantiomeric resolution phenomenon. The crystalline form of the former racemates that underwent the enantiomeric resolution was racemic compounds, while the latter were mixed crystals (solid solutions) composed of the respective optical antipodes. Chirality 9:220–224, 1997.

Regioselective replacement of nitro or sulfonyl group in cyclic α-(nitroalkyl)- or α-(phenylsulfonylalkyl)enones by nucleophiles

Abstract Cyclic α-(nitroalkyl)enones and α-(phenylsulfonylalkyl)enones undergo regioselective substitution of the nitro group by relatively soft sulfur, nitrogen and carbon nucleophiles.

Tellurium Tetrachloride as a Mild Deprotection Reagent for Acetals and Thioacetals

Abstract On treatment with tellurium tetrachloride in dichloromethane at room temperature, acetals and thioacetals are easily cleaved to regenerate original carbonyl compounds in good yields

Me3SiCl promoted conjugate addition of organocuprates to base-sensitive cyclic α-(nitroalkyl)enones

Abstract α-(Nitroalkyl)enones undergo mono β-conjugate addition of organocuprates in the presence of TMSCl to provide the corresponding silyl enol ethers in good to excellent yield, despite the presence of the acidic α-nitro protons.

New substitution reaction of allylic nitro compounds. Regioselective replacement of nitro group in cyclic α-(nitroalkyl)enones by nucleophiles

Abstract Regioselective replacement of nitro group in cyclic α-(nitroalkyl)-enones by various nucleophiles such as stabilized carbanions, amine, NaN 3 , PhSO 2 Na and PhSNa provides the overall S N 2 type products.

Preparation and Properties of Chiral Nitroxide Radicals with Helical Crystal Structure

Abstract A new type of α-asymmetric bicyclic nitroxides were synthesized by three electron reduction of certain homoallylic nitroenones followed by the reaction with nitro-substituted benzoyl chlorides. Some nitroxides thus obtained turned out to exist as a conglomerate (racemic mixture), an equimolecular mixture of two crystalline enantiomers, and hence induced spontaneous optical resolution upon recrystallization. The relationship between the formation of conglomerates and their molecular and crystral structures is described, together with the preliminary results of their paramagnetic susceptibility mesurements.

Preferential enrichment : Mode of polymorphic transformation of a mixed crystal into a racemic compound crystal

Abstract A novel enantiomeric resolution phenomenon observed upon simple recrystallization of the racemates of ST, SC, SN and NNMe3 has been designated as “Preferential Enrichment” in the mother liquor. By the investigation of their crystal properties, it has been suggested that the presence of polymorphism and the resultant polymorphic transformation are responsible for the “Preferential Enrichment.” In this context, on the basis of the molecular alignment and intermolecular interactions in the crystals, a mode of the polymorphic transformation of a metastable mixed crystal (solid solution) of enantiomers into a stable racemic compound crystal is discussed.

Molecular and Crystal Structure and Properties of Te-Containing p-Terphenoquinone Analogues

Abstract p-Terphenoquinone analogues containing a quinonoid type of tellurophene skeleton in the central position have been prepared with a view to developing a new type of organic pnotoconductive materials having amphoteric redox properties. X-ray structure analysis showed that each molecule exhibited an asymmetric boat conformation owing to the bent structure of the whole ring system and the opposite twisting of two terminal rings. The molecular packing manner in the crystals depends on the substituents on the terminal quinonoid rings. These compounds were electrically amphoteric and afforded radical cation salts and CT complexes by electrochemical or chemical oxidation or by the reaction with an appropriate electron acceptor, respectively. Preliminary experimental results on the photoconductive properties of the neutral compound along with the electrical and magnetic properties of the radical cation salts and CT complexes are described.

Crystal structure of a cyclohexanespiropropane derivative prepared from 1-(nitromethyl)-1,2-epoxycyclohexene and methyl sodiocyanoacetate

The structure of 2-hydroxycyclohexanespiro(2′-cyano-2′-methoxycarbonyl)cyclopropane, prepared by the reaction of 1,2-epoxy-1-(nitromethyl)cyclohexane with methyl sodiocyanoacetate, has been determined from X-ray diffraction data. There are two independent molecules in an asymmetric unit. The geometry of cyclopropane is discussed.