The utility of fluoride anion as promoter of the oxidation of Fischer carbene complexes is presented. Two different and complementary methods that allow the fast and convenient preparation of carbene-derived esters in good yields have been developed using stoichiometric or catalytic quantities of fluoride ion.
[reaction: see text] Reaction of alkenyl carbene chromium(0) complexes and ketene acetals triggers the formation of 4-aryl-3,4-dihydrocoumarins. The reaction can be carried out as a simple one-pot protocol in air atmosphere. The huge interest of dihydrocoumarins has prompted us to optimize a multigram-scale process.
Alkynyl Fischer carbene complexes 1, which feature a pendant olefin group, undergo novel cascade processes triggered by [2+2], [3+2], and [4+2] cycloadditions. Competition between cyclopropanation and olefin metathesis is controlled by the substitution at the double bond. The method described can be used to obtain different kind of polycarbo- and -heterocycles. A mechanistic explanation by means of DFT computational modeling is provided.
The reaction of strained bicyclic olefins with alkynyl carbenes and terminal olefins involves the creation of five new sigma C-C bonds with the concomitant formation of two new rings, thus creating a complex and densely functionalized structure in a single operation.
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