RESUMO
In this work, an efficient synthesis of 2-imino-1,3,4-oxadiazolines from acylhydrazides and isothiocyanates is described. In the presence of 4-dimethylaminopyridine (DMAP) and molecular oxygen, various 2-imino-1,3,4-oxadiazolines were produced in good to high yields. The developed method showed a broad substrate scope and was effective on the gram scale. On the basis of the mechanistic studies and previous literature, it was proposed that the mechanism consists of an aerobic oxidation of acylhydrazides facilitated by DMAP and isothiocyanates, followed by a DMAP-mediated annulation of the in situ generated acyldiazenes with isothiocyanates.
RESUMO
A novel Rh(ii)/Brønsted acid catalyzed tandem benzannulation of oxindoles with enaldiazo carbonyls led to the formation of valuable 1-hydroxy-2-acylcarbazoles. This reaction is proposed to involve a formal insertion of a rhodium enalcarbenoid into an oxindole sp(2) C-O bond, an oxa-Michael addition, Friedel-Crafts reaction and a semipinacol type 1,2-carbonyl migration.
RESUMO
A novel rhodium catalyzed pyridannulation of 3-substituted indoles with diazoenals furnished privileged pyrido[1,2-a]indoles. The reaction is proposed to involve a [4 + 2]-annulation of the diacceptor rhodium enalcarbenoid via C-2 functionalization of the indole. The utility of the methodology was demonstrated with a short synthesis of the tetrahydropyrido[1,2-a]indole core, present in a large number of biologically important polycyclic indole alkaloids.
RESUMO
The design of a synergistic rhodium(II) carboxylate and BINOL phosphoric acid catalyzed efficient multicomponent reaction of enaldiazo compounds, arylamines, and aryl aldehydes leading to the first transition-metal-catalyzed direct synthesis of valuable α-pyrrolylbenzylamines is disclosed. The reaction is proposed to involve a transient ammonium ylide of a new class of electrophilic rhodium enalcarbenoid, its regioselective Mannich reaction, and a cyclocondensation cascade. The methodology was used in a highly diastereoselective synthesis of a binaphthyl based chiral pyrrole.
Assuntos
Benzilaminas/síntese química , Ácidos Carboxílicos/química , Pirróis/síntese química , Ródio/química , Aldeídos/química , Benzilaminas/química , Catálise , Estrutura Molecular , Ácidos Fosfóricos/química , Pirróis/química , EstereoisomerismoRESUMO
Disclosed herein is the design of an unprecedented electrophilic rhodium enalcarbenoid which results from rhodium(II)-catalyzed decomposition of a new class of enaldiazo compounds. The synthetic utility of these enalcarbenoids has been successfully demonstrated in the first transition-metal-catalyzed [4+2] benzannulation of pyrroles, thus leading to substituted indoles. The new benzannulation has been applied to the efficient synthesis of the natural product leiocarpone as well as a potent adipocyte fatty-acid binding protein inhibitor.