Epoxides, alcoholysis

The use of other peroxides in the epoxidation of glycals is limited by selectivities that are often inferior to those achieved with DMDO. One notable exception is the use of the wCPBA (m-chloroperbenzoic acid)/KF combination and its recent successful application in one-pot epoxidation alcoholysis (Scheme 5.66) [197]. This involved treatment of benzylated D-galactal 36 in dichloromethane/methanol with a mixture of wCPBA and KF (2 1) in anhydrous dichloromethane to give methyl-2-hydroxygalactoside 165. 

The methatesis of vegetable oils with ethylene is a very interesting way to obtain new unsaturated structures to be transformed into new polyols via the epoxidation - alcoholysis route. Trioleine was used as a model compound (the triester of glycerol with oleic acid), the methatesis reaction with ethylene being catalysed by a special ruthenium catalyst [72]. The resulting triglyceride, with terminal double bonds, after removal of the 1-decene formed, is transformed into polyols by epoxidation, followed by alcoholysis with methanol (reactions 17.27 and 17.28). 

Hydrogenation of styrene oxide over palladium in methanol 66 gives exclusively 2-phenylethanol, but in buffered alkaline methanol the product is l-phenylelhanol. If alcoholysis of the epoxide by the product is troublesome, the problem can be eliminated by portion-wise addition of the epoxide to the reaction, so as always to maintain a high catalyst-to-substrate ratio. The technique is general for reactions in which the product can attack the starting material in competition with the hydrogenation. 

An interesting alcoholysis of epoxides has been reported by Masaki and coworkers <96BCSJ195>, who examined the behavior of epoxides in the presence of a catalytic amount of the Tt-acid tetracyanoethylene (TCNE, 85) in alcoholic media. Ring-opening is very facile under these conditions, typically proceeding via normal C-2 attack, as exemplified by styrene oxide (86). Certain epoxy ethers (e.g., 89) undergo C-1 attack due to anchimeric assistance. Analysis of the reaction mixtures revealed the presence of captodative ethylenes (e.g., 85) formed in situ, whieh were shown to be aetive in eatalyzing the reaction. The proposed mode of catalysis is represented by the intermediate 87. The affinity of these captodative olefins for... 

Lubricants Fatty acid esters could be suitable lubricants, but their resistance to oxidation and tribological properties need to be improved. This can be achieved by epoxidation of the fatty acids followed by alcoholysis of the epoxide (Scheme... 

Enantioselective epoxidation of aUylic alcohols with tantalum surface species prepared by alcoholysis of [(=SiO)Ta(=CH Bu)(CH2 Bu)2j strongly suggests that other transition metals from group 5 and 6 might be used. 

Next to iodine there is also another class of neutral Lewis acids known. Tetracyanoethylene, dicyanoketene acetals and derivatives can catalyse reaction due to their tt-Lewis acid properties. They promoted the alcoholysis of epoxides [238], tetrahydropyranylation of alcohols [239], monothioacetahzation of acetals [240], and carbon-carbon bond formation of acetals [241,242] and imines [243] with silylated carbon nucleophiles. 

Scheme 6.8 Epoxide recognition for epoxide hydrolase that detoxify living cells by catalyzing alcoholysis to water soluble diols. The working model involves the phenolic H-atoms of two tyrosines activating the epoxide for nucleophilic attack. This principle is realized analogously by double hydrogenbonding thiourea catalyst 9 in the natural medium water.

The epoxide ring of methyl crotonate has been reposted to undergo addition of methanol on the carbon atom furthest from the u l<-r function (Eq. 574), giving methyl 2-hydroxy-3-methoxybutyrato.4"5 Alcoholysis of 1,1 -dioarbethoxy-1.2-epoxypropane in the presence of acid has also been carriod cut.1310 Although not definitely established, it is nevertheless probable that addition likewise takes plaoe at thr epoxide carbon atom farthest removed from the ester substituents. 

H3PW12O40 shows a higher activity for the alcoholysis of epoxides [Eq. (15)] than H2SO4, PTS, or HCIO4 (9, 124, 175). While rapid deactivation is observed with H2S04, which is probably due to the formation of an alkyl sulfate, H3PW12O40 maintains its high catalytic activity. 

Alcoholysis of ester and epoxide with various basic catalysts including alkaline earth metal oxides and hydroxides was reported recently by Hattori et alF61 Various alcohols were transesterified with ethyl acetate at 273 K. The results show that in the presence of strongly basic catalysts such as CaO, SrO and BaO, propan-2-ol reacted much faster than methanol, whereas in the presence of more weakly basic catalysts such as MgO, Sr(0H)2-8H20 and Ba(0H)28H20, methanol reacted faster than propan-2-ol. When the alcoholysis was performed with propene oxide, alkaline earth metal oxides were found to be more reactive than hydroxides the reactivity of the alcohols was in the order methanol > ethanol > propan-2-ol > 2-methylpropan-2-ol, regardless of the type of catalyst. 

Hattori, H., Shima, M. and Kabashima, H. Alcoholysis of ester and epoxide catalyzed by solid bases, Stud. Surf. Sci. Catal., 2000, 130D, 3507-3512. 

In the polyurethane industry, the polymeric glycols are prepared by anionic polymerization of epoxides such as ethylene oxide and propylene oxide. Poly(tetra-methylene glycol), which was prepared by polymerization of tetrahydrofuran, was subjected to chain extension by reaction with diisocyanate (polyurethane formation) and with dimethyl terephthalate (polyester by alcoholysis). 

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