RESUMO
Herein we report on the umpolung of Morita-Baylis-Hillman type intermediates and application to the α-functionalization of enone C-H bonds. This reaction gives direct access to α-chloro-enones, 1,2-diketones and α-tosyloxy-enones. The latter are important intermediates for cross-coupling reaction and, to the best of our knowledge, cannot be made in a single step from enones in any other way. The proposed mechanism is supported by spectroscopic studies. The key initial step involves conjugate attack of an amine (DABCO or pyridine), likely assisted by hypervalent iodine acting as a Lewis acid leading to formation of an electrophilic ß-ammonium-enolonium species. Nucleophilic attack by acetate, tosylate, or chloride anion is followed by base induced elimination of the ammonium species to give the noted products. Hydrolysis of α-acetoxy-enones lead to formation of 1,2-diketones. The α-tosyl-enones participate in Negishi coupling reactions under standard conditions.
RESUMO
A double C-H activation and double insertion process to achieve the synthesis benzo[e]indole frameworks has been disclosed. This type of benzannulation is directed by a trifluoromethylketone moiety, which is easy to install on the indole C3-position. Overall the reaction takes places as an oxidative cyclization of two alkynes with the C4-C5 position of indole.
RESUMO
A Rh(iii)-catalyzed C-H activation of indole at the C4-position leading to novel and switchable functionalization has been reported by employing a weakly co-ordinating COCF3 group as a directing group. An additive plays an important role in switching the selectivity between 1,4-addition products and Heck-type products. An acid additive led to the formation of 1,4-addition products whereas a base additive promotes the formation of Heck-type products. Deuteration studies and control experiments were helpful to propose the mechanism.