Facile synthesis of α,β-unsaturated niobium acyls via γ-hydride abstraction

Toward the Synthesis of Biologically Important Chlorins, Isobacteriochlorins, and Corrins. Cyclic Enamides from Acetylenic Amides

“…Tsuji et al have employed similar conditions for effecting methoxycarbonylation of terminal alkynes, and it is possible that acetylenic esters are intermediates in the formation of 21 . However, at present we favor a mechanism in which 20 undergoes CO complexation, followed by migratory insertion, and acyl substitution with MeOH ( cf . dashed arrow in Scheme 4).…”

Hydride Affinities of Arylcarbenium Ions and Iminium Ions in Dimethyl Sulfoxide and Acetonitrile

“…Despite detailed studies on kinetic and thermodynamic effects in hydride transfers, it is clear that C−H heterolysis resulting in carbenium ions is not as well understood as is the formation of carbanions; this is clearly due to the fact that hydride transfer is encountered less frequently in organic systems than is proton transfer. However, hydride abstraction is a common reaction in organometallic chemistry . Recently Bullock and co-workers reported a study of the kinetic hydridicity of a series of metal hydrides, and their rate studies involved hydride transfer to triphenylcarbenium ion (eq 10); however, attempts to determine thermodynamic hydridicities have been less common .…”

Synthesis and Reactivity of Niobium−Vinylketene Complexes Exhibiting Ketene η2-C,O Complexation

“…As seen here, these can lead to the introduction of functional groups not compatible with free ketenes. We have previously shown that the ketene ligands can be liberated from the metal center upon mild oxidation . While we have yet to pursue this with these vinylketenes, this work constitutes a synthetic approach to ketene functionalization involving the “isolated” ketene vinyl substituent.…”

“…Our synthetic approach involves the use of cationic enacyls, which are derived from the ketene complexes. We have previously reported that the complexed ketenes react smoothly with triphenylcarbenium tetrafluoroborate, and that this reaction involves abstraction of a γ-hydrogen and stereospecific formation of the E-enacyls (eq 1; Cp‘ = η 5 -C 5 H 4 SiMe 3 , 2a , R = Ph, 2b , R = Et) or of β-hydrides (to make π-complexed alkenes) .…”