Mechanistic Study of Indolizine Heterocycle Formation by Ruthenium(II)-Assisted Three-Component Cross-Coupling/Cyclization
摘要:
In the presence of the acid HBF4, 3-alkenyl-2-phosphonium indolizines 3a-c can be produced respectively by adding PhC CCOCH3 (2a), CH3OCOC CCOOCH3 (2b), and CH3CH2C CCOCH3 (2c) to a mixture of ruthenium complex RuCl2(PPh3)(3) and the propargyl alcohol (2-Py)CH(OH)C CH (1). We carefully investigated the mechanism of this reaction by means of structurally characterizing two key intermediates, ruthenium vinyl (4) and ruthenium carbene (5), and by deuterium-labeling experiments. A plausible mechanism is proposed, which involves addition of a proton to an alkyne carbon and the insertion of an alkyne into the C alpha bond of an alkenylcarbene group, followed by an alpha-H elimination and reductive elimination.
Mechanistic Study of Indolizine Heterocycle Formation by Ruthenium(II)-Assisted Three-Component Cross-Coupling/Cyclization
摘要:
In the presence of the acid HBF4, 3-alkenyl-2-phosphonium indolizines 3a-c can be produced respectively by adding PhC CCOCH3 (2a), CH3OCOC CCOOCH3 (2b), and CH3CH2C CCOCH3 (2c) to a mixture of ruthenium complex RuCl2(PPh3)(3) and the propargyl alcohol (2-Py)CH(OH)C CH (1). We carefully investigated the mechanism of this reaction by means of structurally characterizing two key intermediates, ruthenium vinyl (4) and ruthenium carbene (5), and by deuterium-labeling experiments. A plausible mechanism is proposed, which involves addition of a proton to an alkyne carbon and the insertion of an alkyne into the C alpha bond of an alkenylcarbene group, followed by an alpha-H elimination and reductive elimination.