Stereoselective Rhodium-Catalyzed 2-C-H 1,3-Dienylation of In-doles-Dual Functions of the Directing Group
A rhodium-catalyzed intermolecular highly stereoselective 1,3-dienylation at the 2-position of indoles with non-terminal allenyl carbonates has been developed by using 2-pyrimidinyl or pyridinyl as the directing group. The reaction tolerates many functional groups affording the products in decent yields under mild conditions. In addition to the C-H bond activation, the directing group also played a vital role in determination of Z-stereoselectivity for the C-H functionalization reaction with 4-aryl-2,3-allenyl carbonates, which is confirmed by the E-selectivity observed with 4-alkyl-2,3-allenyl carbonates. DFT calculation has been conducted to reveal that π-π stacking involving the directing 2-pyrimidinyl or pyridinyl group is the origin of the observed stereoselectivity. Various synthetic transformations have also been demonstrate.