Tetrabutylammonium iodide catalyst, oxidative

Oxidations of C—H bonds at the benzylic or allylic position using -iodanes can be achieved only in the presence of catalysts, such as, iodine, peroxides and transition metals (Section 3.1.20). For example, the oxidation of tetrahydroisoquinoline 209 by iodosylbenzene in the presence of tetrabutylammonium iodide proceeds at the benzylic position to give the lactam 210 (Scheme 3.86) [267]. 

The (diacetoxyiodo)benzene-promoted oxidative iodolactonization of pentenoic acids 347 in the presence of tetrabutylammonium iodide proceeds smoothly at room temperature to afford lactones 348 in high yields (Scheme 3.138) [433]. A catalytic version of this iodolactonization using iodobenzene as a catalyst and sodium perborate monohydrate as the stoichiometric oxidant has also been reported (Section 4.1). 

An efficient metal-free catalytic procedure for aziridination of alkenes using tetrabutylammonium iodide as a catalyst, m-chloroperoxybenzoic acid as the terminal oxidant and A-aminoplittialimide (137) as a nitrenium precursor has been developed (Scheme 4.71) [45],... 

Triazole Derivatives. The synthesis of 4,5-disubstituted 1,2,3-triazoles using sodium polystyrylsulfinate resin 43 was first reported by Huang and coworkers (Scheme 12.17). The synthesis involved the reaction between arylpropiolates and sodium azide followed by oxidation. Resin-bound ethyl polystyrylsulfonylacetate 68 was prepared using ethyl 2-bromoacetate in DMF with potassimn iodide and tetrabutylammonium iodide as a phase transfer catalyst. Subsequent reaction of resin 68 with benzaldehyde using piperidine as a catalyst afforded arylidene polystyrylsulfonyl acetate 69. CycUzation of 69 with sodium azide in DMSO at 120°C for 5h afforded the 1,2,3-txiazoles 70a. 

Most recently, Zhdankin described that the combination of catalytic amounts of tetrabutylammonium iodide (TBAI) with m-chloroperoxybenzoic acid (mCPBA) as a terminal oxidant [77] was the effective catalyst system for the aziridination of various types of alkenes (Scheme 2.53) [78]. The reaction of styrenes with either electron-donating or electron-withdrawing groups afforded the desired aziridines in good yields. Cyclic alkenes and aliphatic alkenes such as 1-decene... 

Benzylic C-H bonds undergo oxidative esterification with TBHP in the presence of tetrabutylammonium iodide as catalyst and carboxylic acids in good to excellent yields. A free radical process has been proposed. Asymmetric epoxidation of electron-poor terminal alkenes bearing different carbonyl groups has been achieved with a cinchona thiourea/TBHP system. The corresponding epoxides, containing a quaternary stereocentre, were isolated in yields up to 98% and enantioselectivity up to 99%. A direct oxidative CDC of indole with A-aryltetrahydroisoquinolines in the 0 presence of a gold catalyst and TBHP resulted in the formation of a variety of alkylated heteroarenes (Scheme 24). ... 

In an extension of this work, the reuse of the polymeric catalyst was addressed and several new PE-poly(alkene) glycol copolymers were prepared [68]. Commercially available oxidized polyethylene (CO2H terminated, both high and low molecular weight) was converted to the acid chloride and reacted with Jeffamine D or Jeffamine EDR, and subsequently converted to the tributylammonium bromide salt with butyl bromide. These new quaternary salts were shown to catalyze the nucleophihc substitution of 1,6-dibromohexane with sodium cyanide or sodium iodide. While none of the polymeric quaternary salts catalyzed the reaction as well as tetrabutylammonium bromide, the temperature-dependent solubility of the polymers allowed removal of the polymer by simple filtration. 

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