A convenient, novel, and metal-free method for the synthesis of 4,4'-diaminotriarylmethanes (DTMs) is described. This process is based on a one-pot condensation of benzylamines with N,N-dimethylaniline derivatives using 4,6-dihydroxysalicylic acid as a co-oxidant and N-iodosuccinimide as an oxidant. To the best of our knowledge, the present method provides the first reported synthesis of DTMs from benzylamines via oxidative C-N bond cleavage and subsequent double C-C bond formations. The obtained DTMs were then easily converted into a series of blue dyes upon treatment with tetrachloro-1,4-benzoquinone (chloranil). Although the production of triarylmethane dyes tends to require the use of toxic heavy metals, the present method is advantageous in that it is a metal-free and straightforward process.
Metal-free, oxidative
four-component Ugi reactions (U-4CRs) were
conducted to synthesize dipeptides from two different amines, isocyanides,
and carboxylic acids using 2,4,6-trihydroxybenzoic acid catalyst in
O2 atmosphere. The organocatalytic U-4CRs proceed via oxidative
cross-coupling of benzylamines with other aliphatic or aromatic amines
to form imines, followed by condensation with isocyanides and carboxylic
acids. The U-4CRs via cross-coupling of amines are rare, and the simple,
metal-free procedures are advantageous for further applications in
drug and heterocycle syntheses.
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