3- Benzyl 1,2,3-triazole 1-oxide

Triazoles can be activated towards electrophiles by the introduction of an A-oxide group. N-Oxidation gives rise to better activation of the 5-position than the 4-position. Thus, bromination of 3-benzyl-1,2,3-triazole 1-oxide (192, R = PhCH2) requires only 120 h at 20 °C and affords the 5-bromo compound (193) in quantitative yield <87ACS(B)724>. 3-Phenyl-1,2,3-triazole 1-oxide is... 

The oxide group mildly activates 3-substituted 1,2,3-triazole 1-oxides to electrophilic attack. Thus, 3-benzyl-1,2,3-triazole 1-oxide reacted much more rapidly than the unoxidized compound in giving the 5-bromo derivative, and there have been a number of other examples of 5-bromination and 5-chlorination of triazole oxides, including that of the 3-phenyl-l-oxide, which was not para-halogenated [87ACS(B)724]. 

Under microwave irradiation and applying MCM-41-immobilized nano-iron oxide higher activity is observed [148]. In this case also, primary aliphatic alcohols could be oxidized. The TON for the selective oxidation of 1-octanol to 1-octanal reached to 46 with 99% selectivity. Hou and coworkers reported in 2006 an iron coordination polymer [Fe(fcz)2Cl2]-2CH30H with fez = l-(2,4-difluorophenyl)-l,l-bis[(l//-l,2,4-triazol-l-yl)methyl]ethanol which catalyzed the oxidation of benzyl alcohol to benzaldehyde with hydrogen peroxide as oxidant in 87% yield and up to 100% selectivity [149]. An alternative approach is based on the use of heteropoly acids, whereby the incorporation of vanadium and iron into a molybdo-phosphoric acid catalyst led to high yields for the oxidation of various alcohols (up to 94%) with molecular oxygen [150]. 

Benzyl-l,2,3-triazole 1-oxides are prone to undergo ring opening when treated with strong bases. Thus 2-(4-methoxybenzyl)-l,2/3-triazole 1-oxide 445 upon treatment with LDA at -78°C in the absence of electrophiles gives rise to 4-methoxybenzyl alcohol 447 as the solely isolable product. A putative mechanism for this transformation is shown in Scheme 128. 

The product obtained by oxidation of cyclopropylamines depends on the structure of the amine. The 4-phenyl-l,2-dihydro-l,2,4-triazole-3,5-dione adduct 1 of 7-benzyl-7-azatricyclo-[4.3.1.0 ]deca-2,4-diene reacted with 3-chloroperoxybenzoic acid to give the corresponding A -oxide 2 in 93 /o yield. Analogously, the sulfinyl A-oxide of tra i-2-(4-chlorophenylsul-fanyl)-Af,A,3,3-tetramethylcyclopropylamine was formed with two equivalents of 3-chloro-peroxybenzoic acid when one equivalent was used only sulfur oxidation to the corresponding sulfinyl derivative occurred. Treatment of cyclopropylamine with hydrogen peroxide in the presence of sodium tungstate, on the other hand, afforded azoxycyclopropane in 50 /o yield." ... 

A stirred suspension of benzoic acid and 6-nitro-l-(2-nitrophenylsulfonyloxy)benzo-triazole in dry dichloromethane treated slowly with triethylamine at 0°, and stirred at room temp, for 2 h - l-benzoyloxy-6-nitrobenzotriazole (Y 88%), in ethanol at 0° treated with NaBH4 over 15 min, and stirred for 2 h at room temp. - benzyl alcohol (Y 80%). The method is simple, mild, and leaves a number of functional groups (nitro, bromine, alkenes) unaffected. F.e. and via 3-acyl-6-nitrobenzotriazole 1-oxides s. T. Okawara et al., Chem. Pharm. Bull. 36, 3628-30 (1988). 

Oxidation of amines containing a-hydrogen atoms is of variable difficulty (equation 23). Permanganate oxidation of l-aryl-5-(tertiary)amino-v-triazoles leads to the corresponding amides. Benzyl(tri-ethyl)ammonium permanganate oxidizes a variety of simple, substituted amines. Tertiary amines give go yields of amides, but secondary and primary amines give moderate yields due to the formation of imines. 

Related Reagents. Allyl Chloroformate Benzyl Chlo-roformate 4-Bromobenzyl Chloroformate t-Butyl Azidoformate l-(t-Butoxycarbonyl)-lEf-benzotriazole 3-A-oxide 1 -(r-Butoxycarbonyl)imidazole 2-(t-Butoxycarbonyloxyimino)-2-phenylacetonitrile A-(t-Butoxycarbonyloxy)phthalimide A-(t-Butoxycarbonyloxy)succinimide V-(r-Butoxycarbonyl)-1,2,4-triazole Di-t-butyl Dicarbonate Ethyl Chloroformate 9-Fluorenylmethyl Chloroformate Isobutyl Chloroformate Methyl Chloroformate 2,2,2-Tribromoethyl Chloroformate 2,2,2-Trichloroethyl Chloroformate 2,2,2-Trichloro-t-butoxycarbonyl Chloride 2-(Trimethylsilyl)ethyl Chloroformate Vinyl Chloroformate. 

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