Deprotection, oxidative

Allyl groups are subject to oxidative deprotection with Chromiapillared Montmorillonite Clay, -BuOOH, CH2CI2, isooctane, 85% yield. Allylamines are cleaved in 84—90% yield, and allyl phenyl ethers are cleaved in 80% yield. 

The oxidative deprotection of silyl ethers, such as the TBDMS ether, has been reviewed. " ... 

Silyl Ethers as Protective Groups for Alcohols. Oxidative Deprotection and Stability Under Alcohol Oxidation Conditions, Muzart. J. Synthesis. 1993, 11... 

The production and synthesis of polymers and medical agents is one of the most interesting potential uses for laccases in synthetic chemistry, where their application has been proposed for oxidative deprotection and the production of complex polymers and pharmaceutical agents. 

Buron et al, published the synthesis of botryllazine derivatives containing a pyrazine core [84]. Scheme 42 describes the synthesis of these compounds. Chloropyrazine 160 was employed as the starting material for the synthesis of the pyrazine chalcone analog 161. 2-Chloro-3-tributylstannylpyrazine 162 was the key intermediate and was coupled with acid chloride 163 to produce the ketone 164. Following protection and subsequent reaction with 165, pyrazine 166 was generated. Oxidation, deprotection, and demetallation produced the pyrazine of interest 161. 

An economical, practical, and environmentally acceptable procedure was elaborated for oxidative deprotection of trimethylsilyl ethers to their corresponding carbonyl compounds. The reaction proceeded in a solventless system, within a short period of time, and yields were good. On irradiation in a conventional microwave for 30 s, trimethylsilyl ether of benzyl alcohol in the presence of mont-morilonite KIO and finely grounded Fe(N03)3 9H2O gave rise to benzaldehyde in 95% yield. The applicability of this method was tested with several aromatic, alicyclic, and aliphatic trimethylsilyl ethers. Duration did not exceed 1 min, and yields were not lower than 80% (Mojtahedi et al. 1999). 

In the case of 489, the product 490 cyclizes to the isoquinolone 491, and the amide substituent is a required part of the target molecule" . However, it frequently occurs that the amide substituent is not required in the final product, and the acid-sensitive alkenyl substituent of 492 has been used as a solution to the problem of cleaving a C—N bond in the product (Scheme 193) ° °. Weinreb-type amides 493 can also be laterally lithiated, and the methoxy group removed from 494 by TiCU" . Hydrazones similarly can be laterally lithiated and oxidatively deprotected. ... 

A new method for conversion of oximes to the corresponding em-halonitro derivatives using NaCl or KBr with Oxone and wet basic alumina was reported (equation 64) °. When the reaction was carried out under the same conditions but by using wet neutral alumina, complex mixtures of compounds in which the parent ketone is the most abundant product (>50%), due to the oxidative deprotection of the oxime, was obtained. 

Hajipour and coworkers prepared benzyltriphenylphosphonium peroxymonosulfate (BnPhsPHSOs) in a very high yield (95%) and purity (99%). This new oxidizing reagent was applied successfully in various deprotection reactions such as the conversion of oximes, phenylhydrazones, 2,4-dinitrophenylhydrazones and semicarbazones to the corresponding carbonyl compounds in the presence of bismuth chloride under nonaqueous conditions . Oxidative deprotection of trimethylsilyl ethers, tetrahydropyranyl ethers and ethylene acetals with BnPh3PHS05 under microwave irradiation affords the corresponding carbonyl compounds in very high yields (equation 71). The same reaction also proceeds under nonaqueous conditions ". 

Oxidative Deprotection of Resin-Bound S-Protected Cysteine Peptides... 

Much of the experience gained in the field of solution-phase oxidative deprotection of cysteine peptides can be applied to solid-phase chemistry. For this purpose the iodine, thallium(III), and chlorosilane/sulfoxide procedures have been usually employed,163 107-1121 generally, the results obtained with the thallium(III) reagent are better than with iodine. 

Thus, oxidation reactions are possible under very mild conditions and with high selectivities. Therefore, this method is especially useful for oxidative deprotections. For example, the oxidative cleavage of the carbon-sulfur bond is easily possible according to Eq. (103). In this way, disulfides and follow-up products of carbenium... 

The third method is oxidative deprotection, which initially results in oxidation to a sulfoxide. Useful oxidizing agents include... 

Keywords trimethylsilyl ether, microwave irradiation, oxidative deprotection, ketone, aldehyde... 

The protection of alcohols as silyl ethers has been reviewed62, as have the relative stabilities of the different trialkylsilyl groups63. Their stability under alcohol oxidation conditions and their oxidative deprotection have been discussed64. Methods for selective deprotection of the various silyl ethers have been the subject of an excellent review65. 

The addition of trimethyl (2-methylallyl)silane 28 to acetal 27 was chosen as the key step. The reaction proceeded smoothly and generated homoallylic ether 29 with high diastereoselectivity. The desired homoallylic alcohol 30 could subsequently be obtained, in high enantiomeric purity, by oxidative deprotection of the chiral template (Scheme 13.12). 

Condensation of 258 with isothiocyanate 7 gave thiourea 417 (80%), which could be cyclized in 70% yield to aminooxazoline 418 using yellow mercuric oxide. Deprotection of 418 by hydrogenolysis afforded (+)-416 (82%) (Scheme 56).106,107... 

Triprotection of the 12-16-membered tetraazacycles was also achieved through organometallic approaches. Chromium(O) or molybdenum(O) tricarbonyl triamino complexes (e.g., 163-165) <1995JOM215> are substituted with acylhalogenides or aldehydes and N-monosubstituted products are obtained after oxidative deprotection in strong acid and acylamide/enamine reduction to amines <1995TL79>. 

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