New Carbanionic Access to 3-Vinylindoles and 3-Vinylbenzofurans
摘要:
[GRAPHICS]A simple route to 3-vinylbenzofurans, 3-vinyifuropyridines, and 3-vinylindoles from readily accessible acetylenic precursors is described. A standard halogen-lithium exchange triggers an irreversible! addition on the triple bond, according to a 5-exo-dig heterocyclization process, followed by a lithium ethoxide elimination. A final isomerization of the exocyclic allene provides a 1,3-dienic system that can react with acrylates, in thermal or hyperbaric conditions, to provide the expected [4+2] cycloadducts.
Carbonickelations of alkynes and functionalization of the resulting vinylnickel moiety have been performed efficiently in a nickel‐catalyzed domino cyclization–condensation process. This reaction, which does not require the preparation of any other organometallic reagent, proceeds only by exo‐dig cyclization. This convenient and mild method constitutes a one‐pot synthesis of substituted dihydrobenzofurans
Reaction of Ni(0) in the presence of iodoarylethers 1 leads, after syn intramolecular carbonickelation of the triple bond, to nucleophilic vinylnickels which can be trapped, in a tandem process, by various electrophiles introduced at the onset of the reaction.
observed. The fact that the E configuration of this adduct was exclusively produced suggests that the reaction proceeds by following an unprecedented anti addition on the alkyne. According to DFT calculations, this unexpected outcome is related to the intramolecular coordination of the lithium by one oxygen atom of the terminal acetal appendage: the O-Li interaction, which persists all along the ring-closure
Is the Elimination of Lithium Alkoxide Easier from a Vinyllithium or from an Alkyllithium? A DFT Study of the Aromatization of 3-Vinylidene-2,3-dihydrobenzofurans to Benzofurans
A possible mechanism for the last step of a cascade transformation in which lithiated propargyl ether 2 is converted into 3-vinylbenzofuran 7 is described. Starting from the lithiated E olefin 3A, our DFT computations show that the final departure of lithium alkoxide is not easy unless an excess of nBuLi, the importance of which has been noted experimentally, prompts a second deprotonation. This theoretical
New Carbanionic Access to 3-Vinylindoles and 3-Vinylbenzofurans
作者:Frédéric Le Strat、Jacques Maddaluno
DOI:10.1021/ol026351v
日期:2002.8.1
[GRAPHICS]A simple route to 3-vinylbenzofurans, 3-vinyifuropyridines, and 3-vinylindoles from readily accessible acetylenic precursors is described. A standard halogen-lithium exchange triggers an irreversible! addition on the triple bond, according to a 5-exo-dig heterocyclization process, followed by a lithium ethoxide elimination. A final isomerization of the exocyclic allene provides a 1,3-dienic system that can react with acrylates, in thermal or hyperbaric conditions, to provide the expected [4+2] cycloadducts.