regioselectivity of cobalt-catalyzed Diels–Alder reactions can be controlled by the choice of ligands on the cobalt center. Ligands of the pyridine-imine type favor the formation of the 1,3-disubstitution pattern on the dihydroaromatic product. The investigation was aimed to elucidate the factors for controlling the regioselectivities and reactivity induced by electroniceffects of the pyridine-imine ligands
Reactions of Alkynyldihaloboranes with 1,3-Dienes. 1,4-Alkynylborations and Stepwise Diels−Alder Reactions
作者:Shun-Wang Leung、Daniel A. Singleton
DOI:10.1021/jo961892h
日期:1997.4.1
alkynylstannanes. The Diels-Alder reactions of 1-4 with isoprene in hexanes proceed rapidly at 25 degrees C, affording 1,4-cyclohexadiene products in high yield with high regioselectivity. Reactions carried out in CH(2)Cl(2) exhibited an alternative product that results from the formal 1,4-alkynylboration of the diene. The alkynylboration intermediates can undergo further conversion to the Diels-Alder adducts under
In situ formation of alkenyl- and alkynylboranes for Diels—Alder reactions by boron—silicon exchange with alkenyl- and alkynylsilanes
作者:Daniel A. Singleton、Shun-Wang Leung
DOI:10.1016/s0022-328x(97)00001-6
日期:1997.10
A variety of alkenylsilanes underwent transmetallation with BBr3 to afford the corresponding alkenyldibromoboranes in solution. Similarly, the transmetallation of alkynylsilanes with BCl3 afforded alkynyldichloroboranes. A number of the alkenyl- and alkynylboranes are novel and useful Diels-Alder dienophiles. An ionic mechanism for the transmetallation is proposed. (C) 1997 Elsevier Science S.A.
Cobalt‐Catalyzed [4+2+2] Cycloaddition for the Synthesis of 1,3,6‐Cyclooctatrienes