Aminophenol oxidative cyclization

Oxidative cyclization of an aminophenol can give rise to a doubly fused oxazine in good yield from two molecules of aminophenol [2331]. A non-oxidative... 

The reductive amination between aldehyde 45 and methyl O-methyl-L-tyrosine ester gave the amino phenol 41, which incorporates all carbon atoms of the synthetic target FR901483. The crucial transformation in the synthetic pathway was the following oxidative cyclization of aminophenol 41. After much experimentation, it was found that exposure of a solution of 41 in hexafluoro-2-propanol to iodobenzene diacetate at room temperature resulted in the formation of azaspiro[4.5]decadienone... 

Aldimines 17 of 2-aminophenol are oxidatively cyclized to 2-substituted benzoxazoles mediated by the hypervalent iodine(III) compound PhI(OAc)2 in CH3OH [288] ... 

The aminophenols are chemically reactive, undergoing reactions involving both the aromatic amino group and the phenoHc hydroxyl moiety, as weU as substitution on the benzene ring. Oxidation leads to the formation of highly colored polymeric quinoid stmctures. 2-Aminophenol undergoes a variety of cyclization reactions. 

Corey s retrosynthetic concept (Scheme 9) is based on two key transformations a cationic cyclization and an intramolecular Diels-Alder (IMDA) reaction. Thus, cationic cychzation of diene 50 would give a precursor 49 for epf-pseudo-pteroxazole (48), which could be converted into 49 via nitration and oxazole formation. Compound 50 would be obtained by deamination of compound 51 and subsequent Wittig chain elongation. A stereocontroUed IMDA reaction of quinone imide 52 would dehver the decaline core of 51. IMDA precursor 52 should be accessible by amide couphng of diene acid 54 and aminophenol 53 followed by oxidative generation of the quinone imide 52 [28]. 

Benzoxazoles are found in a variety of natural products and routinely find use in pharmaceutical research. They are generally made by condensation of a 2-aminophenol with a carboxylic acid or oxidative cylization of an imine intermediate. A mild copper-catalyzed cyclization of o/t/ o-haloanilides to give benzoxazoles 209 has been reported (Scheme 62) <2006JOC1802>. This route is conceptually different to the aforementioned methods in that the starting material is a 2-haloaniline rather than a 2-aminophenol. The reaction conditions tolerate various functional groups in the amide portion of the molecule. 

A direct access to the synthesis of dihydroquinolines (eq 22) was developed. The vinyl quinone mono- or di-SES-imide, accessible by oxidation of the corresponding aminophenol or phenylenediamine, undergoes a thermal 67r-electrocyclization in the presence of a polar nonprotic additive. Dehydrodesulfinylation of the SES group will lead to the quinoline. The vinyl quinone monoimide substrate can also provide the protected indole by photochemical cyclization. 

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