RESUMO
A mechanistic investigation of Ullmann-Goldberg reactions using soluble and partially soluble bases led to the identification of various pathways for catalyst deactivation through (i) product inhibition with amine products, (ii) by-product inhibition with inorganic halide salts, and (iii) ligand exchange by soluble carboxylate bases. The reactions using partially soluble inorganic bases showed variable induction periods, which are responsible for the reproducibility issues in these reactions. Surprisingly, more finely milled Cs2CO3 resulted in a longer induction period due to the higher concentration of the deprotonated amine/amide, leading to suppressed catalytic activity. These results have significant implications on future ligand development for the Ullmann-Goldberg reaction and on the solid form of the inorganic base as an important variable with mechanistic ramifications in many catalytic reactions.
RESUMO
Exposure of a series of ?-(o-haloaryl)-substituted ketones to palladium-catalyzed carbonylation conditions leads to the formation of the corresponding isocoumarins. Balloon pressure of CO is sufficient to achieve high yielding reactions, and both cyclic and acyclic ketones are efficient substrates. The utility of the method is illustrated by a short synthesis of the natural product thunberginol A.
Assuntos
Isocumarinas/síntese química , Paládio/química , Acilação , Monóxido de Carbono , Catálise , Cetonas/química , Fenômenos de Química OrgânicaRESUMO
Palladium-catalyzed intermolecular aminocarbonylation/intramolecular amidation cascade sequences can be used to convert a range of 2-(2-haloalkenyl)aryl halide substrates efficiently and selectively to the corresponding 2-quinolones. Delaying the introduction of the CO atmosphere allows an amination/carbonylation sequence and the preparation of an isoquinolone.
