Acetonitrile epoxidation with

Oxazolines can be obtained by the Lewis acid catalyzed epoxide ring opening of glycidic esters or amides (e.g., 118) with acetonitrile . Oxazolidines are available from the palladium-catalyzed cycloaddition of vinyl epoxides with imines <00H885> or the samarium-promoted reaction of ketimines (e.g., 120) with unfunctionalized... 

Dramatic shape selectivities in competitive olefin epoxidation was observed with picnic basket metalloporphyrins312 313 designed to exclude bulky axial ligands on one sterically protected porphyrin face. When oxidized with PhIO in acetonitrile in the presence of the rigid p-xylyl-strapped porphyrin, cis-2-octene reacted selectively versus ds-cyclooctene or 2-methyl-2-pentene, giving >1000 reactivity ratios.313,314 Some immobilized manganese(III) porphyrins proved to be as efficient as their homogeneous equivalents in epoxidation with PhIO.151,315... 

The transformation of optically active epoxides with acetonitrile into optically active oxazolines (167,168) can be induced by various superacids714 [Eq. (5.264)]. The reaction proceeds with inversion of the asymmetric center with high stereospecificity with anhydrous HF and A1C13, whereas partial racemization is observed in triflic acid (Table 5.39). 

An early report describes the synthesis of fluorohydrins. in low yields, from simple epoxides with anhydrous hydrogen fluoride in diethyl ether containing some water. 1,2-Ep-oxycyclohexanc and 2,2-dimethyloxirane were opened to 2-fluorocyclohexanol in 14% yield and 2-fluoro-2-methylpropan-1 -ol in 20 % yield, respectively, by the same method, but these results could not be reproduced (see also Table 12), With acetonitrile as the solvent, simple epoxides are opened to the fluorohydrins.but yields are low due to side reactions such as oligomerization and rearrangement. 

Less regularly used reagents are tert-hu y hydroperoxide, tf/Y-butyllithium, ozone. dioxiranes, fluorine/water/acetonitrile, or A, A -diethylhydroxylamine. Alkenes carrying a donor substituent can also be epoxidized with pcracids. Fluorinated allylic alcohols give, under Sharpless conditions, epoxides in good yield and enantiosclcclivity. ... 

Ring-opening of Epoxides. A full report has now appeared of the acid-catalysed hydrolysis of 5,6-epoxides in largely non-aqueous media, to give 5(x,6j8-diols. The main conclusions are summarized in last year s report. The opening of epoxides with acetonitrile and an acid has now been extended to a epoxide, predictably giving the 9a-acetamido-lljS-alcohols (see also Part II, Chap. 2, p. 365). " ... 

Unsaturated nitriles are epoxidized with hydrogen peroxide- Tetra-cyanoethylene, after treatment with 30% hydrogen peroxide in acetonitrile at 10-12 °C, furnishes tetracyanoepoxyethane in 59-68% yield [750]. A similar treatment of acrylonitrile gives a 62% yield of glycidamide (epoxy-propionamide) [747]. 

As shown in the Table, with 5 mol% of 1,1-dioxotetrahydrothiopyran-4-one as catalyst,10 epoxidation of various olefins (2-mmol scale) in a homogeneous acetonitrile-water solvent system with 1.5 equiv of Oxone at room temperature can be achieved in a short period of time with excellent yields of epoxides (80-97%) isolated by flash column chromatography.2 As the pH of the reaction is maintained at 7-7.5 by sodium bicarbonate, acid- or base-labile epoxides (entries 12-14) can be easily isolated without decomposition. More importantly, the in situ epoxidation of olefins can be performed on a large scale directly with 5 mol% of tetrahydrothiopyran-4-one, which is oxidized immediately by Oxone to 1,1-dioxotetrahydrothiopyran-4-one during the epoxidation reactions. For example, with 5 mol% of tetrahydrothlopyran-4-one, substrates 3,5 (20 mmol each) and 11 (100 mmol) were epoxidized with excellent isolated yields of epoxides (91-96%). 

However, enantioselectivies were dramatically increased in chloroform (apart from the anomalous reaction with cz-methylstilbene), when compared to those achieved in acetonitrile. We foimd that frans-stilbene, usually a poor substrate with our catalysts, is epoxidized with 67% ee in chloroform, whereas the corresponding reaction, performed in acetonitrile, only affords frans-stilbene oxide with 30% ee. 

The same authors applied the catalyst MCM-41-TBD to the cycloaddition of epoxides with carbon dioxide to give cyclic carbonates [39]. In the model reaction with styrene oxide 101 a comparison of MCM-41-TBD with the homogeneous MTBD under similar conditions (namely 4% molar ratio of TBD w ith respect 101, acetonitrile as solvent at 140 for 20 hours) was carried out (Scheme 26). 

A study of the reactivity induced by irradiation at 254 nm of the epoxides (202) has been carried out. The aim was to study the formation of the ylides (203). The reactions were carried out in acetonitrile solution with ethyl vinyl ether as the addend and are reported to be dependent to some extent on the substitution pattern. Thus, irradiation of (202a) fails to yield an adduct and only the enone (204, 33%) is formed. Epoxides (202b) and (202c) do produce ylides that add to the alkene to yield mixtures of the adducts (205) regiospecifically with a preponderance of the xo-adduct. The epoxide (202d) is also reactive and gives a low yield of the adduct (206, 2%). In general the overall yields are moderate. The... 

The reductive ring opening of 330a with sodium cyanoborohydride/titanium tetrachloride in acetonitrile occurs with no ester reduction whatsoever to provide 421 in 83% yield. Subsequent conversion to the tosylate followed by reduction with lithium borohydride/lithium triethylborohydride affords in 61% yield the crystalline diol 422. Lithium aluminum hydride or sodium borohydride reduction of the tosylate of 421 fails to produce clean reductions to 422. Epoxide ring closure of 422 is achieved with two equivalents of sodium hydroxide in methanol to fiimish in 93% yield (2 S, 3i )-2-benzyloxy-3,4-epoxybutan-l-ol (423) [140] (Scheme 94). 

Jacobsen and Ready <0IJA2687> have reported on the development of a highly aetive cyclic oligosalen catalyst (66), which is remarkably effective in promoting the asymmetric ring opening of epoxides by water and alcohols. For example, exposure of the notoriously recalcitrant substrate cyclohexene oxide (67) to water in methylene chloride/acetonitrile and 1.5 mol% of catalyst 66 led to smooth conversion to the chiral diol 68 in 98% yield and 94% ee. This catalyst is also effective in the kinetic resolution of epoxides with alcohols (i.e., 69 71)<01JA2687>. 

The in situ procedure as proposed by Sonnet et al. (18) is much more attractive for synthetic applications. With the use of only a moderate excess of monopersulfate (C=C KHSO5 = l 2-2.4), they achieved an 80% yield for the epoxidation of oleic acid methyl ester and 81-96% for the epoxidation of various plant oils. It is a twophase reaction with a crown-ether as phase-transfer catalyst yet a considerable amount of inorganic waste (six times the weight of the product) is produced. In a recent work (21), the phase-transfer catalyst was replaced by acetonitrile as a polar solvent. In summary, epoxidation by dioxiranes is a promising new method for oleo-chemistry, especially because it also works in combination with metal catalysts to influence diastereoselectivity (22) an enantioselective epoxidation with sugardioxiranes has also been reported (23). 

Olefins Oxidative Cleavage Photoirradiation (>280 nm) to an acetonitrile solution containing various cyclic and linear olefins with mesoporous silica containing isolated Ti-oxide species produces the corresponding epoxide with high selectivity (>98 %) [2]. 

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