Optically active hydroxyl ester

With optically active tartrate esters present in the reaction system, titanium alkoxides catalyze a very stereoselective oxidation of allylic alcohols. This method must depend on specific interactions in the transition state by which the hydroxyl group controls the relationship between the double bond and approaching reagent and the tartrate establishes a chiral environment at the metal atom. The (+) and (-) enantiomers of diethyl tartrate give enantiomeric epoxides, each in >90% yield." ... 

Thus, the enantiomeric contents in a pair of sulphoxides can be determined by the NMR chemical shifts in the methine or methylene protons in the two diastereomeric complexes which are stabilized by the hydrogen bond between the hydroxyl and the sulphinyl groups147-151 (Scheme 13). Similarly, the enantiomeric purity and absolute configurations of chiral sulphinate ester can be determined by measuring the H NMR shifts in the presence of the optically active alcohols152. 

Yang12 has effected an intramolecular asymmetric carbonyl-ene reaction between an alkene and an a-keto ester. Reaction optimization studies were performed by changing the Lewis acid, solvent, and chiral ligand. Ligand-accelerated catalysis was observed for Sc(OTf)3, Cu(OTf)2, and Zn(OTf)2 (Equation (6)). The resulting optically active m-l-hydroxyl-2-allyl esters provide an entry into multiple natural products. 

In these synthesis, the optically active (R)-cyanohydrin is transformed into the corresponding a-hydroxy carboxylic ester and the hydroxyl funchon is achvated by sulfonylahon. The treatment of the corresponding intermediate with tetra-hydrothieno[3,2-c]pyridine stereoselectively yields the (S)-configured clopidogrel (Scheme 10.23). In the second case, a mutant of the recombinant almond (Pmnus amigdalus) (R)-oxynitrilase isoenzyme 5 catalyzes the formation of enantiopure (R)-2-hydroxy-4-phenylbutyronitrile [54]. Reaction of the sulfonylated hydroxyester derivative with the corresponding dipeptide leads to the formation of enalapril or lisinopril (Scheme 10.24). 

Yashima et al. showed an example where the polymer helicity was controlled by enzymatic enantioselective acylation of the monomers [109]. Optically active phenylacetylenes containing hydroxyl or ester groups were obtained by the kinetic resolution of the corresponding racemic hydroxy-functional phenylacetylene (see Scheme 16). Polymerization of the phenylacetylenes afforded an optically active poly(phenylacetylene) with a high molecular weight (Mn = 89kDa PDI = 2.0) and... 

Optically active ds.vic-diofa.1 It is known that pyridine catalyzes the hydroxyl-ation of alkenes with Os04 and that the osmate ester intermediates form an isolable complex with pyridine (1, 760-761). Hentges and Sharpless reasoned that a similar chiral amine could induce chirality in the diol. And indeed addition of 1 equivalent of 1 or of the C8-diastereoisomer, dihydroquinidine acetate (2), does result in vic-diols in fair to high enantiomeric excess, particularly in reactions performed in toluene at —78°. Opposite stereoselectivities are exhibited by 1 and 2. Optical yields range from 25 to 85%. Use of an amine in which the chiral center is two carbon atoms removed from the coordination site lowers the optical yield to 3 18%. 

In addition to this we have several examples of which the polymer conformation of the polymeric complex leads the asymmetrical selectivity Hydrogenation reactions of 1-methylcinnamic acid and 1-acetamidocinnamic acid by several poly(L-amino acid)-Pd complexes are observed (142-144). Poly(L-valine) (/3-form) and poly(/3-benzyl-L-aspartate) (a-helix, sinistral) give dextrorotative products, and poly(L-leucine) and poly( 3-benzyl-L-aspartate) (a-helix, dextral) do levo-rotatory products. Also, optical active poly-/3-hydroxyl esters-Raney Ni catalyst (145) and Ion-exchange resin modified by optical active amino acid-metal complex (146,147) are observed in asymmetrically selective hydrogenations. 

While these results support a phosphate ester bridge between the glycerol and inositol, it does not prove where the bond is located on the inositol molecule. Inasmuch as the inositol phosphate isolated by alkaline cleavage from the parent phosphatidylinositol or the glycerophosphoinositol was optically active, the phosphate must be attached at the 1 or 4 position. Substitution at the 2 position of inositol would not yield an optically active product. Subsequently as will be discussed, observations from several laboratories have shown that the phosphate bond is between the sn- 3 position of the glycerol and the C-l hydroxyl on myo-inositol. 

Most alkyl carbanions undergo facile pyramidal inversion. Cyclopropyl anions are an exception, presumably because the transition state, with a planar trigonal carbon, is more strained than the ground state. The configurational stability of cyclopropyl anions is of value in the synthesis of deuterated cyclopropanes by the Haller-Bauer reaction (see Section II.B). An interesting dilemma arises when a cyclopropyl anion is stabilized by a n-electron acceptor substituent such as a nitrile or an ester. Will the anion then retain its pyramidal equilibrium geometry for the strain reasons alluded to above, or will it become planar in order to maximize overlap of the filled orbital on carbon with the n orbital of the substituent Walborsky and coworkers addressed this question in a series of experiments in which rates of H/D exchange and racemization were compared for an optically active cyclopropane exposed to a base in a deuterated hydroxylic solvent. The outcome can be illustrated with the particular example of 1,1-diphenylcyclopropane-2-... 

A single enzyme is sometimes capable of many various oxidations. In the presence of NADH (reduced nicotinamide adenine dinucleotide), cyclohexanone oxygenase from Acinetobacter NCIB9871 converts aldehydes into acids, formates of alcohols, and alcohols ketones into esters (Baeyer-Villiger reaction), phenylboronic acids into phenols sulfides into optically active sulfoxides and selenides into selenoxides [1034], Horse liver alcohol dehydrogenase oxidizes primary alcohols to acids (esters) [1035] and secondary alcohols to ketones [1036]. Horseradish peroxidase accomplishes the dehydrogenative coupling [1037] and oxidation of phenols to quinones [1038]. Mushroom polyphenol oxidase hydroxylates phenols and oxidizes them to quinones [1039]. 

The Wharton fragmentation was used as a key step in an approach toward the total synthesis of xenicanes by H. Pfander et al. ° Two optically active substituted frans-cyclononenes were synthesized starting from (-)-Hajos-Parrish ketone. First, the bicyclic 1,3-diol was protected regioselectively on the less sterically hindered hydroxyl group with p-toluenesulfonyl chloride in quantitative yield. Next, the monosulfonate ester was exposed to dimsylsodium in DMSO, which is a strong base, to initiate the desired heterolytic fragmentation. 

Amine Donors. Complexes with l,3-bis[2(S)-aminomethyl-l-pyrrolidinyl]propane and other optically active tetra-amines containing pyrrolidinyl groups with six-membered chelate rings have been studied, and the stereochemistry of the complex depends on the position of the two pyrrolidinyl groups in the ligand. Studies of ability of similar complexes to hydrolyse esters have been reported. Stability constant measurements for nickel(ii) monoamine complexes have been made in a number of hydroxylic solvents. Magnetic and optical spectral measurements of some nickel(ii) succinimide and mixed amine-succinimide complexes indicate that... 

In order to promote selective deprotonation at C-1 in 109, an electron attracting substituent is required at the para position, C-S. The nitrile group was chosen— also because it permitted ready conversion to phenolic hydroxyl at the end of the synthesis (Scheme 15). lodination of sulfone 109 followed by iodide-cyanide exchange gave the C-5 nitrile 115. The optically active acid (-f) 103 (Scheme 14), via its methyl ester (4-) 102, was converted in good yield into iodo olefin 116. 

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