Chiral Glycolates

R)-Pantolactone is also prepared in a sequence involving Claisen rearrangement of the chiral glycolate (24), although with poor enantioselectivity... 

A detailed spectroscopic and theoretical study of the conformation of dioxolanes 1 has appeared <96T8275>, and a theoretical study has shown that the anomeric effect explains the non-planarity of 1,3-dioxole <96JA9850>. The tetraalkynyldioxolanone 2 has been prepared and its structure and reactivity studied <96HCA634>. Both enantiomers of the chiral glycolic acid equivalent 3 can be prepared from D-mannitol <96HCA1696>, and lipase-mediated kinetic... 

Determining the Enantiomer Composition of Chiral Glycols or Cyclic Ketones... 

Chiral glycolates. The chiral dioxolanes 1 and 2 are prepared by reaction of 8-phenylmenthone with a protected derivative, (CH3)3SiOCH2COOSi(CH3)3, of glycolic acid catalyzed by trimethylsilyl triflate. They are obtained in about a 1 1 ratio and are separable by chromatography. Alkylation of the enolates of 1 and 2 proceeds with marked diastereofacial selectivity. After separation of the major... 

Asymmetric acetoxylation of esters.3 Reaction of lead tetraacetate with the silyl enolate of the chiral ester 2 derived from camphorsulfonic acid results in a-acetoxylation with high diastereoselectivity. After crystallization 3 is obtained in 95% de. The product can be hydrolyzed to the optically active a-acetoxy carboxylic acid by K2C03 or reduced to the chiral glycol 4 by LiAlHj. 

The reaction with captodative stabilized radicals is also possible [82]. For instance, the preparation of 1-hydroxycyclopentanecarboxylic acid derivatives from a chiral glycolic acid equivalent is reported [83]. Cyclization and annula-tion procedures are depicted in Eqs. 32 and 33, respectively. 

Menthone-Derived Dioxolanones Chiral Glycolic Acid Derivatives. Acetalization of menthone and phenylmenthone with glycolic acid leads to chromatographically separable mix-... 

Chiral disubstituted PEDOTs have recently been prepared for the first time via transetherification of 3,4-dimethoxythiophene monomers with chiral glycols followed by potentiodynamic oxidation.174 An alternative approach to optically active PEDOTs has also been recently described, which involves the electrochemical polymerization of the EDOT monomer in aqueous hydroxypropyl cellulose (HPC) as a polymer lyotropic liquid crystal to give a chiral PEDOT/HPC hybrid.175 The PEDOT prepared in this chiral nematic liquid crystal exhibited optically active electrochromism in that it could be electrochemically switched between a dark blue reduced state and a sky blue oxidized form that exhibited a different CD spectrum. 

Many other chiral glycols have been prepared. These glycols were used to prepare various chiral crown ether ligands. A few of the chiral glycols are discussed in the next few pages. 

Chiral glycols, 36, 37, 38 Chiral macrocycles, 11, 141, 176 Chiral peraza-cyclophanes, 696 Chiral polyamines, 50, 55 Chiral thiaaza-crown macrcKycles, 474... 

Chiral glycolate equivalents for the asymmetric s)mthesis of a-hydroxy-carbonyl compounds (heterocycles as chiral auxiliaries) 07BCJ1451. 

Tbe preparation of spiro-fused dioxolanes (useful as chiral glycolic enolate equivalents) also employs TMSOTf (eq 13). ... 

Applying this methodology to chiral glycols, Bauerle and coworkers have prepared regio- and stereoregular PEDOTs 49 and demonstrated that the stereochemistry of the monomer influences the electronic properties of the polymer [125]. The synthesis of monomer 50 with an intramolecular disulfide bridge is usable for further functionalization or adsorption on gold. 

Base-catalyzed hydrolysis of the 1,2-chlorohydrin 1 is found to give a chiral glycol 2 with retention of configuration. Propose a reasonable mechanism that would account for this transformation. Include all formal charges and arrows showing the movement of electrons. 

Kikuchi, Y., Kobayashi, K., and Aoyama, Y. (1992) Complexation of chiral glycols, steroidal polyols, and sugars with a multibenzenoid, achiral host as studied by induced circular-dichroism spectroscopy exciton chirality induction in resorcinol-aldehyde cyclotetramer and its use as a supramolecular probe for the assignments of stereochemistry of chiral guests, J. Am. Chem. Soc. 114, in press. 

Scheme 4. Synthesis of chiral glycol ethers starting from (S)-ethyl lactate (13). DHP = dihydropyrane, THP = tetrahydro-pyranyl, Ts = tosyl, Bz = benzyl, THE = tetrahydrofuran, DMF = dimethylformamide.

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