With m CPBA

Alkyl-1,4-dihydropyridines on reaction with peracids undergo either extensive decomposition or biomimetic oxidation to A-alkylpyridinum salts (98JOC10001). However, A-methoxycarbonyl derivatives of 1,4- and 1,2-dihydro-pyridines (74) and (8a) react with m-CPBA to give the methyl tmns-2- 2>-chlorobenzoyloxy)-3-hydroxy-1,2,3,4-tetrahydropyridine-l-carboxylate (75) and methyl rran.s-2-(3-chlorobenzoyloxy)-3-hydroxy-l,2,3,6-tetrahydropyridine-l-carboxylate (76) in 65% and 66% yield, respectively (nonbiomimetic oxidation). The reaction is related to the interaction of peracids with enol ethers and involves the initial formation of an aminoepoxide, which is opened in situ by m-chlorobenzoic acid regio- and stereoselectively (57JA3234, 93JA7593). 

An interesting oxidative ring-opening reaction is shown in Scheme 2.36. Oxidation of vinylaziridines 138 with m-CPBA gave 142 through [2,3] Meisenheimer... 

Methods A oxidation with m-CPBA, B oxidation with (-l-)-MPCA. 

Oxidation of oximes to nitro compounds with m-CPBA has been applied to the synthesis of dialkyl 1-nitroalkanephosphonates (Eq. 2.63),124 which are useful reagents for conversion of carbonyl compounds to nitroalkenes.125... 

The most effective and frequently used oxidant of secondary amines in organic solvents (CH2CI2, CH3CN, MeOH) is m-chloroperbenzoic acid (m-CPBA). Oxy-dation with m-CPBA of seco-curane type indoline alkaloids of strychnobrasiline (32), in deacetylated form, gives the corresponding nitrones (33), (34), and (35) (Scheme 2.12) (86). 

Oxidations of a range of p-cyanoethyl tertiary amines (44) with m-CPBA in CH2CI2 give the corresponding A-oxides (45), which can be isolated or undergo Cope elimination affording hydroxylamines (46) in high yields (Scheme 2.16) (Table 2.1) (96). Hydroxylamines (46) can be easily oxidated into nitrones (see Section 2.2.1.3). 

Oxidative ring opening of isoxazolidines leads to nitrones. Thus, bicyclic isox-azolidines (50) and (51), treated with m-CPBA, afford nitrones (52), (53), (54), and (55) (Scheme 2.19). Conformational analysis has confirmed the key role of the nitrogen lone pair with respect to regioselectivity of the reaction and of the intramolecular kinetic deprotonation of the intermediate oxoammonium derivative (125). 

Similar oxidative ring opening occurs in other bi- and tricyclic isoxazolidines upon treatment with m-CPBA (126, 127). 

Oxidation with m-CPBA of monocyclic isoxazolidines (56) without H at a-C gives a tautomeric mixture of acyclic nitrones (57) and six-membered cyclic hydroxylamines (58), with their proportion depending on the substituents... 

Next is the construction of the D ring. The TMS enol ether of compound 111 undergoes oxidation with m-CPBA, providing the C-5a trimethylsilyloxy ketone 112. Addition of methyl Grignard reagent to the ketone group and subsequent dehydration provides compound 113. Osmylation of the C=C double... 

The rhodium-catalyzed hydroboration has opened the way to cyclization reactions starting from dienes [92], For instance, rhodium-catalyzed hydroboration of the terminal alkenyl group of an os/Tunsaturated lactone followed by reaction with the PTOC-OMe chain transfer reagent afforded the bicyclic a-S-pyridyl lactone in 63% yield (Scheme 39). After oxidation of the sulfide with m-CPBA, thermal elimination of the sulfoxide afforded the corresponding a-methylene lactone in 65% yield. Interestingly, such bicyclic a-methylenelactones are substructures that can be found in many natural products such as mirabolide [93]. 

Peroxyacids are powerful oxidants and so side reactions are to be expected. Ketones are known to undergo Baeyer-Villiger " oxidation to the carboxylic acid ester on treatment with peroxyacids and so these by-products can be observed if oxime hydrolysis occurs during the oxidation. Paquette and co-workers " " observed such a by-product (61) during the oxidation of the dioxime (59) to the dinitro compound (60) with m-CPBA in hot acetonitrile. 

Dinitrocubane (28) has been synthesized by Eaton and co-workers via two routes both starting from cubane-l,4-dicarboxylic acid (25). The first of these routes uses diphenylphos-phoryl azide in the presence of a base and tert-butyl alcohol to effect direct conversion of the carboxylic acid (25) to the tert-butylcarbamate (26). Hydrolysis of (26) with mineral acid, followed by direct oxidation of the diamine (27) with m-CPBA, yields 1,4-diiutrocubane (28). Initial attempts to convert cubane-l,4-dicarboxylic acid (25) to 1,4-diaminocubane (27) via a Curtins rearrangement of the corresponding diacylazide (29) were abandoned due to the extremely explosive nature of the latter. However, subsequent experiments showed that treatment of the acid chloride of cubane-l,4-dicarboxylic acid with trimethylsilyl azide allows the formation of the diisocyanate (30) without prior isolation of the dangerous diacylazide (29) from solution. Oxidation of the diisocyanate (30) to 1,4-dinitrocubane (28) was achieved with dimethyldioxirane in wet acetone. Dimethyldioxirane is also reported to oxidize both the diamine (27) and its hydrochloride salt to 1,4-dinitrocubane (28) in excellent yield. ... 

Aniline virtually quantitatively reacts with the corresponding anhydride in refluxing toluene in the presence of triethanolamine to form N-phenylmaleimide 189, whose oxidation with m-CPBA affords imsymme-trical sulfone in 67% yield (08CC3281). N-Substituted compounds were synthesized in a similar way starting from (2-methylbenzo[b]thiophen-3-yl)maleic anhydride and /J-alanine 190a or 5-amino-l,10-phenanthroline... 

Epoxidation of 632c with m-CPBA to 634, followed by silylation with bis(trimethylsilyl) acetamide (BSA) to 635, and TMSOTf-indnced cyclization gives 6-hydroxymethyl-3-phenyl-l,2,4-trioxane 636 (Scheme 181) °. Epoxides 638, which are characterized by geminal dimethyl substitnents, are obtained by m-CPBA oxidation of the (0-3,3-dimethyl-allyl)hydroperoxy acetals 637. While the strnctnral change in 638, as compared to epoxide 634, direct the acid-catalyzed cyclizations to the endo mode yielding the 7-membered... 

Epoxidation of monoterpenic olefins and A -octalins with dimethyloxirane gives the corresponding epoxides in excellent yields. Some A -octalins are oxidized in a much more stereoselective manner than with m-CPBA . ... 

Sato and coworkers reported recently an interesting oxidation reaction of 1,4-dihydro-l,4-diphenyl-2,3-benzodithiin . When compound 38 was treated with m-CPBA in CH2CI2, ring contraction to l,3-diphenylbenzo[c]thiophene 39 was observed. With H2O2 in CH3COOH, the reaction afforded l,3-dihydro-l,3-diphenylbenzo[c]thiophene 40, while with Oxone a highly regioselective oxidized product, i.e. l,4-dihydro-l,4-diphenyl-2,3-benzodithiin 2,2-dioxide 41, was formed (equation 58). 

As part of an extensive study of the 1,3-dipolar cycloadditions of cyclic nitrones, Ali et al. (392-397) found that the reaction of the 1,4-oxazine 349 with various dipolarophiles afforded the expected isoxazolidinyloxazine adducts (Scheme 1.78) (398). In line with earlier results (399,400), oxidation of styrene-derived adduct 350 with m-CPBA facilitated N—O cleavage and further oxidation as above to afford a mixture of three compounds, an inseparable mixture of ketonitrone 351 and bicyclic hydroxylamine 352, along with aldonitrone 353 with a solvent-dependent ratio (401). These workers have prepared the analogous nitrones based on the 1,3-oxazine ring by oxidative cleavage of isoxazolidines to afford the hydroxylamine followed by a second oxidation with benzoquinone or Hg(ll) oxide (402-404). These dipoles, along with a more recently reported pyrazine nitrone (405), were aU used in successful cycloaddition reactions with alkenes. Elsewhere, the synthesis and cycloaddition reactions of related pyrazine-3-one nitrone 354 (406,407) or a benzoxazine-3-one dipolarophile 355 (408) have been reported. These workers have also reported the use of isoxazoles with an exocychc alkene in the preparation of spiro[isoxazolidine-5,4 -isoxazolines] (409). 

Subsequently, we examined several MFA derivatives as substrates for the Pt/C>2 reaction. When 32 was subjected to Pt/(>2 chemistry, three products (132-134) were isolated in poor yield [Fig. (36)]. In the case of 23, the Pt/C>2 reaction mixture was treated straightaway with m-CPBA without isolation of any intermediate products, giving the desired compound 10 (43% yield). Compound 10 can be converted to PHA (2) in three steps. Compound 132 was converted to PHA (2) by treatment with alane-dimethylethyl amine complex in THF (30% yield). 

When 36 was subjected to Pt/02 chemistry [Fig. (37)], four products (35, 135-137) were isolated. Although the Pt/02 chemistry performed on 36 does give 137 (the desired product) in trace amounts, it can be more readily prepared by oxidation of 136 with m-CPBA (80% yield). Subsequently, 137 was reduced with LAH/AICI3 in THF to give 138 (40% yield). 

Direct oxidation of aromatics with m-CPBA in a two-phase system affords the most stable so-called K-region arene oxides in moderate yields.805 Careful control of pH is necessary to avoid acid-catalyzed rearrangement of the acid-sensitive product epoxides. The new powerful oxidants, dimethyldioxiranes,81,82 have also been used to convert arenes to arene oxides.806... 

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