Diol monoesters cyclic

The alternative method of reduction of such hydroxyketones is the a //-selective Evans intramolecular delivery of nucleophilic hydride through a cyclic transition state. In Janda s bryostatin synthesis, the diol monoester 182, produced by kinetic resolution with an immobilised lipase (chapter 29) is reduced to the an//-diol 183 by acetoxy-borohydride. The hydride delivery is intramolecular through a chair transition state 184. This is 1,3-control via a cyclic transition state (chapter 21).30... 

This reaction has been extended to other cyclic and open-chain 1,2-diol monoesters. ... 

A chiral recognition was observed in aminolysis of 3-acyl-4(R)-methoxycarbonyl-l,3-thiazolidine-2-thione, a derivative of (R)-cysteine, by racemic amines to give an optically active amide [(S)-excess] and amine [(R)-excess]264). In the reaction of cyclic meso-1,3-diols with chiral N-protected phenylalanyl chlorides, Yamada et al.26S) observed the preferential formation of one of the two possible diastereomeric monoesters, which has been used for the synthesis of optically active steroids 266) and prostaglandins 267). 

Several review articles on biodegradable polymers and polyesters have appeared in the literature [12-22]. Extensive studies have been carried out by Al-bertsson and coworkers developing biodegradable polymers such as polyesters, polyanhydrides, polycarbonates, etc., and relating the structure and properties of aliphatic polyesters prepared by ROP and polycondensation techniques. In the present paper, the current status of aliphatic polyesters and copolyesters (block, random, and star-shaped), their synthesis and characterization, properties, degradation, and applications are described. Emphasis is placed primarily on aliphatic polyesters derived by condensation of diols with dicarboxylic acids (or their derivatives) or by the ROP of cyclic monoesters. Polyesters derived from cyclic diesters or microbial polyesters are beyond the scope of this review. 

The formation of diol-periodate esters is supported by physical evidence. The addition of ethane-1,2-diol to periodate solutions causes an initial rapid change in the uv absorption spectrum, followed by a slower change as the oxidation proceeds and lOJ is formed. Similar results are observed for other 1,2-diols except for highly substituted diols such as pinacol (Buist et al ). Buist and Bunton have shown that the cyclic periodate esters formed in alkaline solution from 1,2-diols and periodate can be detected by nmr. The initial fall in pH which occurs in the oxidations of ethane-1,2-diol and lightly substituted diols is also attributed to ester formation (Malaprade, Buist and Bunton ). Cyclic triesters, similar to the cyclic diesters formed from 1,2-diols, are formed from cyclic compounds containing the cis-l,2,3-triol system (Barker and Shaw , Dijkstra and from 1,2-0-isopropylidene-a-D-glucofuranose. In the latter case the presence of the triester has been demonstrated by nmr (Berlin and van Rudloff ). Monoesters of periodic acid have not been detected in any system, but they are postulated as intermediates in the formation of cyclic diesters from 1,2-diols (section 1.3.5). 

A spectroscopic study (i.r. and n.m.r.) of the monoesters of trifluoroacetic acid with the diols HO-CHa-CHa-OH, HO CHaCMea-OH, and HO CMea CMea OH has shown that with the pinacol ester (27), significant amounts of the cyclic tautomer (28) are present at equilibrium in various solvents (CCI4, 60% CsHe, 72% MeCN, 95% 1,4-dioxan, 95%) considerably smaller amounts of the corresponding trichloroacetate cyclic tautomer are present at equilibrium (CCU, 7% MeCN, 13%). ... 

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