Mechanism and Origins of Regio- and Enantioselectivities in Rh-I-Catalyzed Hydrogenative Couplings of 1,3-Diynes and Activated Carbonyl Partners: Intervention of a Cumulene Intermediate

作者：Liu Peng; Krische Michael J^*; Houk Kendall N

来源：Chemistry - A European Journal, 2011, 17(14): 4021-4029.

DOI：10.1002/chem.201002741

• C-C coupling
• density functional calculations
• enantioselectivity
• reaction mechanisms
• regioselectivity
• rhodium

The mechanism of the rhodium-catalyzed reductive coupling of 1,3-diynes and vicinal dicarbonyl compounds employing H-2 as reductant was investigated by density functional theory. Oxidative coupling through 1,4-addition of the Rh-I-bound dicarbonyl to the conjugated diyne via a seven-membered cyclic cumulene transition state leads to exclusive formation of linear adducts. Diyne 1,4-addition is much faster than the 1,2-addition to simple alkynes. The 1,2-dicarbonyl compound is bound to rhodium in a bidentate fashion during the oxidative coupling event. The chemo-, regio-, and enantioselectivities of this reaction were investigated and are attributed to this unique 1,4-addition pathway. The close proximity of the ligand and the alkyne substituent distal to the forming C-C bond controls the regio- and enantioselectivity: coupling occurs at the sterically more demanding alkyne terminus, which minimizes nonbonded interaction with the ligand. A stereochemical model is proposed that accounts for preferential formation of the (R)-configurated coupling product when (R)-biaryl phosphine ligands are used.

• 出版日期2011-3