We report here a C–H homoallylation
reaction of aromatic
ketones with methylenecyclopropanes (MCPs) only using
a catalytic amount of Fe(PMe3)4. A variety of
aromatic ketones and MCPs are applicable to the reaction to form ortho-homoallylated
aromatic ketones selectively via regioselective scission of the three-membered
rings. The homoallylated products are amenable to further elaborations,
providing functionalized 1,2-dihydronaphthalenes.
Here we report an ortho-C–H alkenylation
of aromatic ketones with unsymmetric internal alkynes catalyzed by
an iron phosphine complex, Fe(PMe3)4. The use
of a catalytic amount of P
t
Bu3 as an additive was found to improve the product yields. The alkenylation
proceeds regio- and stereoselectively to give the corresponding styrene
derivatives.
Deuterium-labeling experiments were performed for the Fe(PMe3)4-catalyzed C–H/olefin coupling using a deuterium-labeled aromatic ketone with various alkenes. While the reactions with a variety of alkenes provided the linear alkylation products formed via 1,2-insertion of alkene into an Fe–H bond, the reversible 2,1-insertion proceeded during the reaction highly depends on the choice of the alkene. No H/D scrambling resulting from 2,1-insertion/β-elimination was detected for the reactions with a vinylsilane and N-vinylcarbazole, but the reactions with styrenes are considered to involve rapid 2,1-insertion/ β-elimination processes to cause significant levels of H/D scrambling.
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