MCPBA oxidation

The preparation and stereochemistry of some indole alkaloid N-oxides was studied by Sakai and co-workers (276). The N-oxidation of yohimbine (74) with m-chloroperbenzoic acid under mild reaction conditions led to two isomeric N-oxides (556 and 557) in a ratio of 10 1. MCPBA oxidation of pseudoyohimbine (88) afforded a single product (558). 

Sulfonylallenes 130a-c are easily prepared from propargyl alcohol via sulfenation, [2,3]-sigmatropic rearrangement and mCPBA oxidation (see Chapter 1). 

The telluroxide elimination shows a preference towards the less substituted carbon (as observed by the 2.48-2.50 1 ratio assessed in the elimination of 2-bromooctyl phenyl telluroxide and 2-bromodecyl phenyl telluroxide) that is more marked than that observed for the selenoxide and sulphoxide eliminations. By procedure b (MCPBA oxidation), the ratio is decreased to 1.5-1.7 1. 

These adducts, submitted to MCPBA oxidation, undergo telluroxide elimination, regenerating the original C=C bond. The overall transformation therefore provides a-hydroxy-alkylation of a,jS-unsaturated carbonyl compounds. ... 

Diepoxyalkene derivatives (all stereoisomers) were synthesized from 5Z, 6Z, 9Z) trienes with a Ql. Ci9 or Ci8 straight chain, lymantriid sex pheromones, and their candidates were synthesized by MCPBA oxidation of optically active epoxyalkadienes. ... 

A sulfenate ester analogous to but with methyl Instead of chlorine Is formed on MCPBA oxidation of the corresponding methallyl thlocarbamate this patent report ( ) does not mention any Intermediates or speculate on the mechanism of the reaction. Formation of the sulfenate ester Is conveniently monitored not only by IR and NMR but also by CI-MS, In the latter case because In contrast to the sulfoxides (7, 9) the sulfenates are sufficiently stable to exhibit a strong molecular Ion (7 ). 

Different isomers of C qO have been prepared by photooxygenation [48], by MCPBA-oxidation [48], by ozonolysis [49] or they were extracted from fullerene soot [11, 50]. Isolation from fullerene soot and analysis of the product of photooxygenation and thermal ozonolysis yields only [6,6]-closed epoxide structures. As already observed for CgoO, ozonolysis and subsequent photolysis of the ozonide C7QO3 gives different [5,6]-open oxidoannulene structures [49]. 

MCPBA oxidation of thiepins (149) and (150) to form the 1-oxide and 1,1-dioxide derivatives (75AG(E)812) occurs in high yield. The peroxyacid oxidant assumes the role of electrophile in the initial oxidation step. 

Compound 42 was synthesized following the pubhshed method [40], The yield of the mCPBA oxidation of 42 to afford 6 was less than 50% and involved a cumbersome isolation procedure. This oxidation is the most environmentally unfriendly step in the synthesis of 6. The addition of one gram of oxygen to the sulfide generates more than ten grams of m-chlorobenzoic acid as a waste. Thus, this transformation is not green, and furthermore mCPBA is an expensive and shock-sensitive material. 

The preparation of a-hydroxy carbonyl compounds has been accomplished by the oxidation of enolates using both oxygen6 and MoC PyHMPA-(MoOPh).7 Acyl anion equivalents offer another route to this useful class of compounds. The procedure presented here for the synthesis of 6-hydroxy-3,5,5-tr1methyl-2-cyclohexen-l-one illustrates the use of MCPBA oxidation of an enol silyl ether as a method for obtaining an a-hydroxy enone. The procedure is a scaleup of a published synthesis. ... 

The sulfoxide 195 was prepared by MCPBA oxidation of the corresponding sulfide.56... 

Chiral Davis oxaziridines allow the oxidation of phosphonates to a-hydroxy-phosphonates in good ee with apparently wide generality and with a sense of induction that is well controlled by the chirality of the reagent used.109 mCPBA oxidation of a bi-cyclic e do-camphorylsulfonylimine surprisingly resulted in an exo-camphorylsulfonyl-oxaziridine, whereas all other camphorylsulfonylimines resulted only in endo-oxaziiidines.110 Asymmetric oxidation of sulfides to sulfoxides and the a-hydroxylation of enolates were predicted by models in which steric interactions are minimized. 

The regioselectivity of the migration in Baeyer-Villiger oxidation of ketones is very dependent upon substituents attached to carbon atoms adjacent to the ketone. In a study128 of the MCPBA oxidation of polyhydroxycyclohexanone derivatives, the regioselectivity of the reaction has been carefully identified. This should prove useful to synthetic chemists when planning to use this type of reaction, since cyclitols are important synthons in natural product synthesis. 

Only the. svw-epoxide 191 is formed on MCPBA oxidation of the imidazolyl cyclohexene 190 this selectivity apparently reflects hydrogen bonding between the imidazole and... 

The regioselectivity in the epoxidation of ethenylidenecyclopropanes by MCPBA strongly depends on the double-bond substituents. Thus, with alkyl substituents such as methyl 195, the adjacent electron-rich double bond is epoxidized, whereas the diphenyl analogue 196 reacts preferentially on the other double bond both primary products undergo subsequent rearrangements308. The MCPBA oxidation of the hindered cumulene 197 gave the cyclopropanones 198 and 199309. 

After florisil (magnesium-silicate) filtration and concentration, crude 18 was treated with a THF solution of a 1 1 mixture of sodium iodide and mcte-chloroperoxybenzoic acid (MCPBA) yielding in 67 % (from 5) the a-iodo ketones 6.8 The ratio of diastereomers in this mixture was not described further. Mechanistically MCPBA oxidizes the iodide ion to an iodoniumion-species, which reacts with the double bond, generating intermediate 21. After TMS is removed the tricyclic iodonium ion collapses to desired 6. In contrast to this transformation the researchers observed no useful yields by direct treatment of the silyl enol ether with molecular iodine. 

The oxidation of 3,4-di(l-adamantyl)-l,2-dithiete 116a and 3,4 - d i -ft rft b u t y 1 -1,2 - d i t h i c t c 116b as well as 3, 3, 7, 7 -tetramethylcyclohepteno[l, 2 -r ]-l,2-dithiete 116c was investigated. It was found that w-chloropcrbcnzoic acid (MCPBA) oxidation of 1,2-dithietes 116 with 1 equiv of the oxidant afforded the corresponding 1,2-dithiete. 9-oxides 117, while oxidation with an excess (2-3 equiv) of this oxidant produced a mixture of isomeric (EE-, EZ-, and ZZ-) bis-sulfines 119 via the corresponding 1,2-dithiete Ah -dioxide intermediates 118 (Scheme 13). The oxidation... 

The reaction of silyl enol ether 275 with mCPBA gave a-siloxyketones 277 through oxycarbocations 276 (equation 175)1. Paquette and coworkers isolated siloxyepoxide 278 as the initial product in the mCPBA oxidation of a silyl enol ether and determined the structure by X-ray structural analysis435. 

The fact that these adducts were diastereoisomerically pure (deduced from the reported melting points and NMR spectra) suggests that these reactions took place with a complete control of the diastereoselectivity. Bearing this in mind, in 1989 Waldner [64] synthesized optically pure sulfoxide 55 (by MCPBA oxidation of the corresponding chiral thioether and further separation from the epimeric mixture so obtained) and studied its reactions with dienes and aza-dienes (Scheme 29). A high 7r-facial selectivity (almost complete with cyclopen-tadiene and azadienes) was observed in all cases, the approach of the diene from the dienophilic face supporting the lone pair of electrons at sulfur being favored. In the case of the reaction with cyclopentadiene, the endo-selectivity was complete as well. 

Racemic diesters 82 (Scheme 42), containing the bis-sulfoxide moiety incorporated into a five-membered ring, have also been used as dialkoxycarbonyl ketene equivalents [82]. They react with cyclopentadiene in 7-12 h at room temperature, affording mixtures of two adducts. The relative configuration of 82 was not unequivocally determined, but it was speculatively assigned on the basis of the conformational preferences of the precursor monosulfoxide and the presumably favored steric course of its MCPBA oxidation. We must point out the unexpectedly similar reactivity of dienophiles 80 and 82, which is very difficult to explain given the increase in the dienophilic reactivity that two ester groups usually induce in ethylenic systems. 

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