Perbenzoic acid, epoxidation

Perbenzoic acid and monoperphthalic acid are used in the same manner as MCPBA but a fresh solution of these reagents is usually required syntheses for these reagents can also be found in Fieser and Fieser s Reagents for Organic Synthesis. A microtechnique for perbenzoic acid epoxidation has also been described. ... 

Reaction of 6-methoxy-l-tetralone (30) with methylmagnesium iodide gave the dihydronaphthalene (31) in high yield (Scheme 4). However, the transformation of 31 to the tetralone 33, via perbenzoic acid epoxidation followed by acid workup, was capricious and resulted in low yields. A better route was developed, involving hydroboration (hydrogen peroxide oxidation) to the alcohol 32, followed by Pfitzner-Moffatt oxidation to the tetralone 33 in an overall yield of 61%. Other oxidation methods were tried but with varied and poor results. Alkylation of the tetralone 33 with 3-bromopropyne yielded 34, which underwent hydration [mercury (II) acetate in acetic acid-formic acid] to the diketone (35). The enone (36) obtained by base catalyzed cyclization was ster-eospecifically reduced with lithium aluminum hydride to the allylic alcohol... 

Ethylenic compounds when oxidised with perbenzoic acid or perphthalic acid in chloroform solution yield epoxides (or oxiranes). This Is sometimes known as the Prileschajew epoxidation reaction. Thus pyrene affords styrene oxide (or 2-plienyloxirane) ... 

The most common method of epoxidation is the reaction of olefins with per-acids. For over twenty years, perbenzoic acid and monoperphthalic acid have been the most frequently used reagents. Recently, m-chloroperbenzoic acid has proved to be an equally efficient reagent which is commercially available (Aldrich Chemicals). The general electrophilic addition mechanism of the peracid-olefin reaction is currently believed to involve either an intra-molecularly bonded spiro species (1) or a 1,3-dipolar adduct of a carbonyl oxide, cf. (2). The electrophilic addition reaction is sensitive to steric effects. 

Several steroid olefins, especially A -steroids, do not give exclusive a-epoxidation. The a-oxirane usually predominates in the epoxidation mixture, its proportion varying from 50% to 90% or greater when either perbenzoic acid or monoperphthalic acid is employed. The claims that the ratio of a- to p-epoxide is high in compounds containing a keto group d or a j5-substituent at may be misleading since epoxidation of 17a,20 20,... 

The presence of functional groups on the steroid nucleus can affect the course of the epoxidation reaction thus epoxidation of 3/ -chlorocholest-4-ene (11) gives the 4a,5a-epoxide in 97 % yield, whereas the 3a-chloro group hinders (presumably sterically) attack on the 4,5-double bond towards the a-face of the molecule. The 3a-acetoxy function similarly influences the selectivity of the epoxidation of cholest-4-enes, a 53 47 mixture of the respective 4 , 5a- and 4jS, 5jS-epoxides being obtained after exposure of the 3a-acetoxy-4-ene (13) to perbenzoic acid. 

In a typical Knof procedure, 3jS-hydroxyandrost-5-en-17-one acetate is epoxidized with perbenzoic acid (or m-chloroperbenzoic acid ) to a mixture of 5a,6a- and 5)5,6)5-epoxides (75) in 99 % yield. Subsequent oxidation with aqueous chromium trioxide in methyl ethyl ketone affords the 5a-hydroxy-6-ketone (76) in 89% yield. Baeyer-Villiger oxidation of the hydroxy ketone (76) with perbenzoic acid (or w-chloroperbenzoic acid ) gives keto acid (77) in 96% yield as a complex with benzoic acid. The benzoic acid can be removed by sublimation or, more conveniently, by treating the complex with benzoyl chloride and pyridine to give the easily isolated )5-lactone (70) in 40% yield. As described in section III-A, pyrolysis of j5-lactone (70) affords A -B-norsteroid (71). Knof used this reaction sequence to prepare 3)5-hydroxy-B-norandrost-5-en-17-one acetate, B-noran-... 

Photo-addition of allene to the enone (90) yield adduct (91) in 75 % yield, which was subjected to ketalization in 77% yield. Epoxidation of (92) with perbenzoic acid followed by chromatography on alumina afforded two expoxides (93) and (94). Both (93) and (94) could be converted separately through (95) and (96) respectively which was the common intermediate leading to isoishwarane (98) and ishwarane following a deketalization-retroaldol-aldol process to furnish the keto-alcohol (97) (99) 30>. 

Perbenzoic acid reacts with alkenes at low-temperatures (0-25°) to give high yields of epoxides. 

Endrin is a stereoisomer of dieldrin produced by the reaction of vinyl chloride and hexachloro-cyclopentadiene to yield a product which is then dehydrochlorinated and condensed with cyclopentadiene to produce isodrin. This intermediate is then epoxidized with peracetic or perbenzoic acid to yield endrin. An alternative production method involves condensation of hexachlorocyclopentadiene with acetylene to yield the intermediate for condensation with cyclopentadiene (EPA 1985e IARC 1974). 

The molybdenum-mediated arylamine cyclization was also applied to the total synthesis of pyrano[3,2-a]carbazole alkaloids (Scheme 26). Reaction of the 5-aminochromene 71 with the complex salt 62 affords the complex 72, which on oxidative cyclization provides girinimbine 73, a key compound for the transformation into further pyrano[3,2-a] carbazole alkaloids. Oxidation of 73 with DDQ leads to murrayacine 74, while epoxidation of 73 using meta-chloro-perbenzoic acid (MCPBA) followed by hydrolysis provides dihydroxygirinim-bine75 [113]. 

II, 20-dione, which is reacted with methylmagnesium bromide in the presence of lithium bromide to give 3a-hydroxy-16a-methylpregnan-ll,20-dione (27.1.39), after which a Ha-hydroxyl group is added. This is done by a reaction with acetic anhydride in the presence of p-toluenesulfonic acid, forming the 3-acetoxy-17-enolacetate 27.1.40, which is epoxidized by perbenzoic acid 27.1.41, and the product is hydrolyzed by an alkali to give an oxyketone... 

The rate of epoxidation of cyclohexene with perbenzoic acid decreases with increasing solvent polarity. The epoxidation by poly(peracrylic acid) shows the opposite trend. A polar solvent causes the polar polymer to swell to a greater extent and the reaction rate is increased due to a higher local concentration of cyclohexene [Takagi, 1975]. 

Diddrin [60-57-1] or l,2,3,4,10,10-hexachloro-l,4,4tf,5,8,8tf-hexahydro-6,7-epoxy-l,4- dvx< 5,8-dimethanonaphthalene (34) (mp 176°C, vp 0.4 mPa at 20°C) is formed from aldrin by epoxidation with peracetic or perbenzoic acids. It is soluble in water to 27 //g/L. Aldrin and dieldrin have had extensive use as soil insecticides and for seed treatments. Dieldrin, which is very persistent, has had wide use to control migratory locusts, as a residual spray to control the Anopheles vectors of malaria, and to control tsetse flies. Because of environmental persistence and propensity for bioaccumulation, registrations in the United States were canceled in 1974. 

Perbenzoic acid is used for the conversion of olefinic compounds into epoxides. 

The epoxidation reaction is achieved most conveniently by employing m-chloroperbenzoic acid (or perbenzoic acid) in a solvent such as chloroform. The use of other peracids, such as peracetic acid or pertrifluoroacetic acid, give lower yields of the oxirane since the oxide may be readily cleaved to form the monoester of the diol (e.g. Section 5.4.5, p. 547). 

A O-Diacetyldihydropseudosolasodine (12a) gave the epimeric pyrrolidines (13) on treatment with bromine. When N-bromosuccinimide was used as oxidant, the ketone (12b) and the pyrrolidine (14) were also formed.17 The WolfF-Kishner reductions of solasodenone (9b) and of the epimeric 4,5 -dihydro-analogues have been reported.18 Solasodine gave the expected 5a,6-epoxide on treatment with perbenzoic acid.19 The preparation of an intermediate in the synthesis of the solanidine alkaloids has been reviewed.20... 

The epoxide 6 is naturally electrophilic, but where does the epoxide come from By far the most important method of epoxide synthesis is the treatment of alkenes 19 with peroxy acids RCO3H 21. Alkenes are naturally nucleophilic 2 they react with bromine to give dibromides 20 and with electrophilic peroxyacids 21 to give epoxides. Again, these reactions convert nucleophilic alkenes into electrophilic derivatives. A very popular reagent for epoxidation is mCPBA (meta-chloro-perbenzoic acid) 21 R = 3-chlorophenyl but many other compounds are used. 

Diastereoselective epoxidations.6 Epoxidation of the ergoline 1 with m-chloro-perbenzoic acid provides the a-epoxide (2) with high diastereoselectivity and yield. In contrast, epoxidation via the bromohydrin provides the (1-oxide (2) in equally high diastereoselectivity. Osmylation of 1 also provides the 5a,6a-diol selectively (7 1) with similar preference for the a-face. 

Addition of halogens produces dihalides, of which, for example, a dibromide crystallizes easily but is very unstable.7 Perbenzoic acid oxidizes L-rhamnal to L-rhamnose.7 The primary oxidation product, probably an epoxide, upon treatment with anhydrous methanol gives methyl diacetyl-a-L-rhamnoside.38 Crystalline 2-desoxy-L-rhamnose was prepared from L-rhamnal.18-3 ... 

---