Diols from epoxidation

Scheme 3.42. Synthesis of cyclohexan-1,3-diols from epoxides containing a C=C-double bond.

Kishimoto Y, Ogawa I (2004) Amine-catalyzed, one-pot coproduction of dialkyl carbonates and 1, 2-diols from epoxides, alcohols, and carbon dioxide. Ind Eng Chem Res 43(26) 8155-8162... 

Although diborane (BH3)2 reduces epoxides, it usually gives a mixture of products in addition to the usual alcohols. The reduction of styrene oxide derivatives with diborane has been studied in order to develop a new route to 1,3-diols from epoxides (equation 19).4 a,3-Unsaturated epoxides undergo... 

From the standpoints of both cost and atom economy, water is the ideal nucleophile for synthesis of enantioenriched C2-symmetric 1,2-diols from meso-epoxides. 

An alternative method for generating enriched 1,2-diols from meso-epoxides consists of asymmetric copolymerization with carbon dioxide. Nozaki demonstrated that a zinc complex formed in situ from diethylzinc and diphenylprolinol catalyzed the copolymerization with cyclohexene oxide in high yield. Alkaline hydrolysis of the isotactic polymer then liberated the trans diol in 94% yield and 70% ee (Scheme 7.20) [40]. Coates later found that other zinc complexes such as 12 are also effective in forming isotactic polymers [41-42]. 

Diols from Lithium P-Lithioalkoxides Generated by the Reductive Lithiation of Epoxides 2,5-Dimethyl-2,4-hexanediol. 

In contrast to 21, the diol epoxide derivative of the 8,9-dihydrodiol of DMBA was relatively stable. Although only the anti isomer was isolated and identified from epoxidation of the 8,9-dihydrodiol with m-chloroperbenzoic acid (84), it is likely that the syn isomer may also be formed in this reaction. The 8,9-dihydrodiol exists predominantly in the diaxial conformation as a consequence of steric interaction between the 8-hydroxyl and 7-methyl groups (88). 

The asymmetric oxidation of organic compounds, especially the epoxidation, dihydroxylation, aminohydroxylation, aziridination, and related reactions have been extensively studied and found widespread applications in the asymmetric synthesis of many important compounds. Like many other asymmetric reactions discussed in other chapters of this book, oxidation systems have been developed and extended steadily over the years in order to attain high stereoselectivity. This chapter on oxidation is organized into several key topics. The first section covers the formation of epoxides from allylic alcohols or their derivatives and the corresponding ring-opening reactions of the thus formed 2,3-epoxy alcohols. The second part deals with dihydroxylation reactions, which can provide diols from olefins. The third section delineates the recently discovered aminohydroxylation of olefins. The fourth topic involves the oxidation of unfunc-tionalized olefins. The chapter ends with a discussion of the oxidation of eno-lates and asymmetric aziridination reactions. 

DIOLS FROM LITHIUM [5-LITHIOALKOXIDES GENERATED BY THE REDUCTIVE LITHIATION OF EPOXIDES ... 

B. Mudryk and T. Cohen 173 1,3-DIOLS FROM LITHIUM p-LITHIOALKOXIDES GENERATED BY THE REDUCTIVE LITHIATION OF EPOXIDES 2,5-DIMETHYL-2,4-HEXANEDIOL... 

Photodegradation. Casida s group (15, 20) has studied the photodecomposition of R-20458 on silica gel and in water. The major aqueous photoproducts are summarized in Figure 1. The predominant photoproduct in aqueous solution resulted from epoxide hydration to the corresponding diol. The photoproducts on silica were quite similar to aqueous products with an enhanced yield of diepoxide and diminished yield of diol. Photosensitizer dyes had little effect on R-20458 photodegradation. 

Kureshy R. I. Khan N. H. Abdi S. H. R. Patel S. T. Jasra R. V. (2002) Simultaneous produetion of chirally enriched epoxides and 1,2 diols from racemic epoxides via hydrolytie kinetic resolution (HKR/, J Mol Catal, 179 73-77. 

Enantiopure epoxides and vicinal diols are important versatile chiral building blocks for pharmaceuticals (Hanson, 1991). Their preparation has much in common and they may also be converted into one another. These chirons may be obtained both by asymmetric synthesis and resolution of racemic mixtures. When planning a synthetic strategy both enzymic and non-enzymic methods have to be taken into account. In recent years there has been considerable advance in non-enzymic methods as mentioned in part 2.1.1. Formation of epoxides and vicinal diols from aromatics is important for the break down of benzene compounds in nature (See part 2.6.5). 

In conclusion, the chiral salen Co(III) complexes immobilized on Si-MCM-41 colud be synthesized by multi-grafting method. The asymmetric synthesis of diols from terminal olefins was applied with success using a hybrid catalyst of Ti-MCM-41/chiral Co(III) salen complexes. The olefins are readily oxidized to racemic epoxides over Ti-MCM-41 in the presence of oxidants such as TBHP, and then these synthesized diols are generated sequentially by epoxide hydrolysis on the salen Co(lll) complexes. This catalytic system may provide a direct approach to the synthesis of enantioselective diols from olefins. 

However, should you wish to make both syn and anti-diols from an alkene when only one isomer (E- or Z-) can be made, such as cyclopentene 25, you need another method. Epoxidation... 

Already in the first reports on olefin oxidation with the MTO/H2O2 system [3], it was noted that the formation of diols from the desired epoxides, caused by the Br0nsted acidity of the system, is a major drawback of this system. The solution for this problem was found in the same report by the addition of a nitrogen base. This method has been explored extensively since and has become an important factor in the MTO-catalyzed olefin epoxidation. 

One recent publication from the group of Abu-Omar reports on a condensation reaction involving glycerol and furfural, both renewables, to produce dioxolanes, formally a dehydration reaction. Here, a cationic oxorhenium(V) oxazoline species is used as the catalyst for the formation of various 1,3-dioxalanes from furfural with diols or epoxides under mild conditions (Scheme 21). Especially interesting is the reaction of furfural with glycerol to obtain a 70 30 mixture of the corresponding 1,3-dioxolane and 1,3-dioxane in solvent-free conditions [125]. 

Cyclic sulfates provide a useful alternative to epoxides now that it is viable to produce a chiral diol from an alkene. These cyclic compounds are prepared by reaction of the diol with thionyl chloride, followed by ruthenium-catalyzed oxidation of the sulfur (Scheme 9.26).166 This oxidation has the advantage over previous procedures because it only uses a small amount of the transition metal catalyst.167168... 

Fig. 11.5. Os-catalyzed asymmetric dihydroxylation of olefins by enantiomeric differentiation (chiral induction). (Reprinted from S. Torii, Electrochemical Asymmetric Syntheses of Chiral Diols and Epoxides Interface, Winter 1997, p. 46, Scheme 1. Reproduced by permission of the Electrochemical Society.)...

To make a polymer it is necessary to react aryl diisocyanates with diols. Some important polymers -of the type, called elastanes, are made by using long-chain aliphatic diols from partly polymerized epoxides, rather like those discussed in the last section, and reacting them with diaryl diisocyanates to give a pre-polymer . 

Peracids themselves produce epoxides and diols from alkenes but are not powerful enough to oxidize these further by cleaving the carbon-carbon bond. However, in the presence of transition metals they will cleave alkenes and diols to give, usually, carboxylic acids. For example, peracids in combination with ruthenium compounds are well known in this capacity (Figure 3.31).146,147 Warwel and co-workers have reported the cleavage of alkenes using peracetic acid and the ruthenium catalyst, Ru(acac)3.148... 

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