RESUMO
A novel phosphonium-mediated reaction of isatins is described. In the presence of alcohol, the reaction proceeds to furnish C-12 modified tryptanthrin derivatives. Without alcohol, self-dimerization of isatins gives rise to tryptanthrin and its analogs. This divergent and step-economic approach provides a facile access to diverse indoloquinazoline structures including the natural alkaloids, methylisatoid and cephalanthrin B, in high yields from simple precursors under mild and metal-free reaction conditions.
RESUMO
An atom- and step-economic synthesis of aryliminophosphoranes bearing ortho urea was achieved via unprecedented Ph3P-I2 mediated ring-opening of 1,3-dihydro-1H-benzimidazol-2-ones with secondary amines. Tandem aza-Wittig/heterocyclization of the functionalized aryliminophosphoranes upon treatment with isothiocyanates enables a facile access to a single regioisomer of N1-substituted 2-aminobenzimidazoles as well as fused tetracyclic quinazolinone derivatives in one-pot. 31P{1H} NMR studies suggested that the urea C-N bond of benzimidazolone is weakened by N-phosphorylation, leading to aminolysis rather than the expected deoxygenative amination.
RESUMO
Instead of the expected substituted 2-aminobenzo[d]oxazoles, relatively stable ring-opened oxyphosphonium betaines were isolated for the first time from the Ph3P-I2-mediated reactions of benzo[d]oxazol-2(3H)-ones with acyclic secondary amines. The structure of one of these compounds was unambiguously confirmed by single-crystal X-ray analysis. Thermolysis of the betaines gave rise to 2-dialkylaminobenzoxazoles with concomitant loss of triphenylphosphine oxide, suggesting their possible role as intermediates in an alternative reaction path.
