Study of the mechanism of optical resolutions via diastereoisomeric salt formation

Racemic malic acid (I) was resolved by R-α-phenylethylamine(II). The S-(?)-I.R-(+)-II diastereoisomer was in excess in the precipitated salt. DSC curves and X-ray powder diffractograms proved that the diastereoisomeric salt mixture precipitated during the resolution was isomorphous with the optically pure S-(?)-I.R-(+)-II salt. The diastereoisomeric salt mixture containing the R-(?)-I.R-(+)-II salt in abundance bound crystal solvate (water or methanol) when produced by the total evaporation of the mother liquor, while the optically pure R-(?)-I.R-(+)-II salt crystallized without solvate. It is generally assumed that solid solution formation takes place when the two diastereoisomers are alike and the high similarity results in less efficient enantiomer separation. This paper demonstrates that efficient resolution can be accomplished in case of solid solution formation too. The diastereoisomeric salt mixtures can crystallize in isomorphic form even when the physico-chemical properties of the optically pure diastereoisomeric salts are quite different.     

Study of the mechanism of optical resolutionsvia diastereoisomeric salt formation

The products obtained in the optical resolution of the N-methylamphetamine by the Pope-Peachy method, using half equivalent R, R-tartaric acid and half equivalent hydrochloric acid in absolute ethanol were investigated by thermoanalytical methods. The DSC measurements of the precipitated salts provide sufficient information for following the progress of the resolution. In this way, the results of the resolution can be estimated with the precision of about 5% optical purity.     

通过硼氢化-原位再结晶提高二异松莰烷基硼烷光学纯度的简便方法

本文叙述了由国产低光学纯(43.6%e e)(-)-α-蒎烯通过硼氢化-原位再结晶, 制备高光学纯(97.2%ee)(+)-二异松茨烷基硼烷(diisopinocampheylborane, Ipc2BH)的简便新方法。     

A convenient cyclopropanation process of oxindoles via bromoethylsulfonium salt

A practical convenient conversion of oxindoles into the corresponding spirocyclopropyl oxindoles is achieved efficiently using bromoethylsulfonium salt, which is easily prepared on a large scale and is stable crystalline. This reaction of bromoethylsulfonium salt with different substituted unprotected oxindoles proceeded under mild condition and provided moderate yields.     

A convenient method for the formation of internucleotide linkage

Internucleotide linkage can be made readily by reaction of $\text{N}$-unprotected nueleosides and phosphorochloridates or $\text{p}$-nitrophenyl phosphates by the assistance of Grignard reagents.     

The influence of molecular structure and crystallization time on the efficiency of diastereoisomeric salt forming resolutions

Reciprocal resolutions between compounds (racemates and enantiomers) with similar structures have been examined. Amongst structurally similar compounds (so called relative structures) several N-acyl amino acids and amino acid esters were investigated. A part of the resolving agent or the racemic compound could be replaced by an achiral compound with a relative structure and an additive could occasionally improve significantly the efficiency of the resolution. Both the kinetic and the thermodynamic controls were observed as governing factors of the reciprocal resolutions.     

A convenient synthesis of new aminopyrroloindoles via an imminium salt

Cyclization of pyrrolidinocarboxamide derivative of 2-(1-pyrrolyl) benzoic acid leads to an imminium salt which conduct to N-substituted 9-imino (and amino) 9H-pyrrolo[1,2-a]indoles.     

A convenient synthesis of new aminomethylenedioxypyrroloindoles via an iminium salt

Cyclization of 2-(1-pyrrolyl)piperonylcarboxamide derivatives gave iminium perchlorates which afforded 9-(N-substituted-imino) and 9-(N-substituted amino)-6,7-methylenedioxypyrrolo[1,2-a]indoles.     

A new method for designing optical resolutions and for determination of relative configurations

A new method has been elaborated for designing optical resolutions via diastereoisomeric salt formation, based upon the principle of three point interaction. In our method the favourite resolving agent to a given racemate and suitable resolution method can be found, and it can be predicted which enantiomer is expected in excess in the crystallized diastereoisomeric salt.     

Supra-assembled membranes for optical resolutions

Optical resolutions through self-assembled membranes were carried out by using poly(pyrrole) (PPy) doped with chiral anionic polymers such as poly(L-glutamic acid) or dextran sulfonic acid. Preferential permeations of either L- or D-Tryptophane occurred through the PPy membranes.     

A convenient method for 3-pyrroline synthesis

[reaction: see text]. The synthesis of a range of 3-pyrrolines has been achieved from primary amine starting materials using a two-step alkylation/alkylidene carbene CH-insertion reaction sequence. We have shown that insertion into a range of CH-bond types is possible, and the formation of nitrogen-bearing quaternary stereocenters is a relatively facile process. The insertion reaction occurs with >95% retention of stereochemistry, but the presence of protecting groups on nitrogen is generally deleterious to the cyclization process.     

A new convenient synthesis of aroyl cyanides via the formation of cyanohydrin nitrate intermediates

The treatment of α-bromoarylacetonitriles with AgNO₃ generates cyanohydrin nitrate intermediates, which easily eliminate nitrous acid with the formation of carbonyl bond to afford aroyl cyanides in good to high yields.     

Supramolecular membranes for optical resolutions and molecular recognitions

Poly(L-glutamate) having amphiphilic side chains was designed as membrane materials for optical resolution of α -amino acids. Solvent- cast films of the poly(L-glutamate) had a self-ordered structure containing α-helix of the poly(L-glutamate). Optical resolutions of various amino acids were carried out through the thin membranes of the amphiphilic poly(L-glutamate). Racemic mixtures of Tryptophan were completely separated through the membrane. Mechanism of the optical resolutions was investigated in terms of molecular recognitions of racemic Tryptophan by the ordered structure of the mambrane.     

A convenient method for the synthesis of roflumilast

A convenient synthetic method has been developed for the synthesis of roflumilast from 4-difluoromethoxy-3-hydroxybenzaldehyde and bromomethyl cyclopropane via O-alkylation, oxidation and N-acylation. With sodium hydroxide as alkali in the last step, the total yield of roflumilast can be up to 68.3 % and the purity of the target product reached 99.2 %. It was obvious that sodium hydroxide showed more economic advantage for scale-up production than sodium hydride or potassium tert-butoxide.     

A convenient method for synthesizing modified 4-nitrophenols

[reaction: see text] Beta-nitroenamine having a formyl group behaves as the synthetic equivalent of unstable nitromalonaldehyde upon treatment with ketones under basic conditions and leads to 2,6-disubstituted 4-nitrophenols. The present method is safer than the conventional one using sodium nitromalonaldehyde and enables the preparation of hitherto unknown nitrophenols.     

A convenient method for the synthesis of electron-rich phosphonates

Very electron-rich benzylic-type phosphonates can be prepared by treating the corresponding alcohols in triethyl phosphite with one equivalent of iodine at an appropriate temperature in a general one-pot process.