Synergistic steric effects in the development of a palladium-catalyzed alkyne carbohalogenation: stereodivergent synthesis of vinyl halides.
We report our finding that by exploiting the synergistic steric effects between substrate and catalyst, an intramolecular Pd-catalyzed alkyne carbohalogenation can be achieved. This operationally simple method uses the bulky Pd/Q-Phos combination and allows access to tetrasubstituted vinyl halides from the corresponding aryl chlorides, bromides, and iodides. Steric effects in the substrate play a key role by promoting C sp 2-halogen reductive elimination and enabling catalytic turnover. Through a reversible oxidative addition mechanism, a thermodynamically driven isomerization reaction is observed at elevated temperatures. Thus by changing the reaction temperature, both stereoisomers of the reaction become readily accessible.
Department of Chemistry, University of Toronto, 80 St. George St. Toronto, Ontario (Canada) http://www.chem.utoronto.ca/staff/ML/index.php.
Christine M
CM
Le
Perry J C
PJ
Menzies
David A
DA
Petrone
Mark
M
Lautens
carbohalogenation; cyclization; palladium; reversible oxidative addition