Ethylene glycol, chiral

Near baseline resolution of the two diastereoisomers of soman can be obtained on nonpolar columns under normal analysis conditions and complete resolution can be obtained on more polar columns such as poly (ethylene glycol) Chiral resolution of the four iso-... 

Asymmetric Diels-Alder reactions have also been achieved in the presence of poly(ethylene glycol)-supported chiral imidazohdin-4-one [113] and copper-loaded silica-grafted bis(oxazolines) [114]. Polymer-bound, camphor-based polysiloxane-fixed metal 1,3-diketonates (chirasil-metals) (37) have proven to catalyze the hetero Diels-Alder reaction of benzaldehyde and Danishefsky s diene. Best catalysts were obtained when oxovanadium(lV) and europium(III) where employed as coordinating metals. Despite excellent chemical yields the resulting pyran-4-ones were reported to be formed with only moderate stereoselectivity (Scheme 4.22). The polymeric catalysts are soluble in hexane and could be precipitated by addition of methanol. Interestingly, the polymeric oxovanadium(III)-catalysts invoke opposite enantioselectivities compared with their monomeric counterparts [115]. 

Nitrophenyl)ethylene glycol was used to protect simple aldehydes and ketones, as well as some steroids. Acetals were prepared under acid catalysis, leading, in the case of chiral carbonyl compounds to diaste-reoisomers. The photochemical removal of the protecting group was in several instances complicated by the instability of some carbonyl derivatives to irradiation at 350 nm otherwise, yields were in the range of 83-90% (see Scheme 19). 

Both the (RR)- and (5S)-enantiomers of hydrobenzoin (Figure I4a) have been made to react (110, 117, 118) successfully in a (2 + 2) cyclization with ethylene glycol ditosylate in the presence of bases (e.g., NaOH in dioxane or NaH in MA -dimethylformamide) to give the enantiomeric tetiaphenyl-18-crown-6 derivatives (RRRR)-73 and (SSSS)-73. The corresponding optically pure tetra-anisyl, tetra-a-naphthyl, and tetra-/3-naphthyl-18-crown-6 derivatives 74, 75, and 76, respectively, have also been prepared in similar fashion (119). It should be noted that (RRRR)- and (,SSSS)-73 have also been obtained as a result of a base-promoted (1 + 1) cyclization (120) between the chiral extended diol and... 

Very recently, the synthesis of a series of chiral poly(9,9 -spirobiflu-orene)crown ethers [e.g., (SS)-139, (SSSS)-140, (SSSSSS)-141, and (S55SSS5S)-142] with 26-, 52-, 78-, and 104-membered rings have been described (162). The last three are rare examples of compounds with C4, 5, and Cg synunetries, respectively. They were isolated chromatographically from a reaction mixture consisting of (S)-2,2 -bisbromomethyl-9,9 -spirobifluorene, ethylene glycol, KOr-Bu, and Csl in tolune. 

BACM, CHD/ TEPIC Thermal, — Poly(ethylene) glycol 200 and 300 100pm I.D., HPLC of small molecules, chiral separations [40]... 

If a diastereomeric mixture of (S,S)-2,5-dimethyl-3.4-hexanediol esters 2 and 3 reacts with methylmagnesium bromide, the result is kinetic resolution, as verified for R1 = Bn. The diastereomeric mixture was prepared from the racemic ethylene glycol a-chloro boronic ester via transesterification with chiral diol. The products isolated were (S,S)-2,5-dimethyl-3,4-hexanediol [(/ )-2-phcnyl-l-methylethyl]boronate, diastereomeric ratio >95 5 as indicated by the rotation of the (/ )- -phenyl-2-propanol derived by deboronation with hydrogen peroxide, and (S,S)-2,5-dimethyl-3.4-hexanediol methylboronate. Phenylacetaldehyde was identified by 1H NMR4. 

Precolumn (achiral) poly (ethylene glycol) or a suitable polar stationary phase Analytical column (chiral) ... 

The chiral crown ethers 101,102,104,105, and 152, andpodands 100 and 153 were formed from isomannide by introducing ethylene glycol units as... 

The CSPs prepared by the molecular imprint technique have also been used for chiral resolution by CEC [98-100]. Lin et al. [91] synthesized L-aromatic amino acid-imprinted polymers using azobisnitriles with either photoinitiators or thermal initiators at temperatures ranging from 4°C to 60° C. Methacrylic acid (MAA) was used as the functional monomer and ethylene glycol dimethacrylate (EDMA) was used as the cross-linker. The resulting polymers were ground and sieved to a particle size less than 10 pm, filled into the capillary columns, and used for enantiomeric separations of some amino acids at different temperatures. The relationships of separation factor and column temperatures were demonstrated to be linear between the logarithm of the separation factors and the inverse of the absolute temperature (Fig. 24). The authors also compared the obtained chiral resolution with the chiral resolution achieved by HPLC and reported the best resolution on CEC. The chromatograms of the chiral resolution of dl-... 

Benaglia M, Celentano G, Cinquini M, Cozzi F, Puglisi A (2002) Poly(ethylene glycol)-supported chiral imidazolidin-4-one an efficient organic catalyst for the enantioselective diels-alder cycloaddition. Adv Synth Catal 344 149-152... 

Chiral polymer-supported thiiranes 401 were prepared by free radical copolymerization of TMA ((3)-thiiranylmethyl-methacrylate) and ethylene glycol dimethacrylate (EDMA) (Equation 60) <2006TA1944>. These chiral thiiranes were transformed into polymer-supported aminothiols by the facile ring opening of the thiirane group with benzylamine and methylamine. These derivatives, complexed with [RuCl2(p-cymene)]2, were used in assymmetric reduction of acetophenone to gave (A)-l-phenylethanol (39% ee from methylamine and 50% ee from benzylamine derivatives). 

Carbohydrate crown ethers were obtained with ethylene spacers from a crown ether point of view, the carbohydrate vicinal diols are replacing one ethylene glycol unit [181,182], Cyclic compounds synthesized include bis-gluco-15-crown-5 82, bis-gluco-21-crown-7, and tetra-gluco-24-crown-8 (O Scheme 14). These chiral macrocycles could serve as catalysts in the asymmetric Michael addition of methyl a-phenylacetate to methyl acrylate. With the goal to study molecular interactions, P,P, and Q, Q -bis-maltosides with aliphatic two-, three-, or four-earbon spacers were synthesized [183]. Spaced cyclodextrins were prepared to study their supramolecular properties [184,185]. 

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