Direct Observation of Oxidative Cyclization of η²-Alkene and η²-Aldehyde on Ni(0) Center. Significant Acceleration by Addition of Me₃SiOTf

Abstract

Direct oxidative cyclization of (eta2:eta2-CH2=CHCH2C6H4CHO)Ni(PR3) to form the nickelacycle and drastic acceleration of the cyclization by the addition of Me3SiOTf were observed. (eta2-PhCHO)Ni(PCy3)2 also reacted with Me3SiOTf to give (eta1:eta1-Me3SiOCH(Ph))Ni(PCy3)OTf.

Nickel-catalyzed coupling reactions of alkenes

“…Pivotal to our work was Ogoshi's observation that a Lewis acid, such as a silyl triflate, facilitated the formation of an oxanickellacycle through cyclization of an α,ω-enal [13]. We proposed that if the intermolecular coupling of an alkene and aldehyde occurred, the nickel alkyl bond could undergo a β-hydride elimination, followed by the removal of triflic acid from nickel to regenerate the nickel catalyst.…”

“…Ogoshi described a nickel-promoted reductive cyclization of enals, but this process was stoichiometric in nickel [13]. Later on, several examples of catalytic, intramolecular alkene-ketone coupling reactions were reported [14].…”

Highly Atom Economical Molecular Transformation via Hetero-Nickelacycle

“…It has been reported that hetero-nickelacycles react with carbon monoxide to give the corresponding cyclic carbonyl compounds. 7 In fact, the reaction of 4ab with carbon monoxide at room temperature proceeded smoothly to give the γ-lactam 7a quantitatively (eq 8). 6a Although the stoichiometric reaction of hetero-nickelacycles with carbon monoxide proceeds smoothly to afford the cyclic carbonylated compounds quantitatively, no nickel-catalyzed carbonylative cyclization reaction has been reported to date due to the formation of nickel carbonyl complexes unreactive to unsaturated compounds.…”

“…First, the stoichiometric reaction of phenyl formate and amine with 4aa was conducted in DMF-d 7 and quantitative formation of γ-lactam was observed. The yield of 7a decreased when the reaction was carried out in C 6 D 6 .…”

“…The coordination of aromatic aldehydes to nickel (0) The intra-molecular oxidative cyclization of an alkene and an aldehyde with nickel(0) was reported in 2004, which was the first direct observation of oxidative cyclization of an alkene and an aldehyde with nickel(0) and the molecular structure of isolated oxa-nickelacycle dimer was confirmed by X-ray crystallography. 7 The generated oxa-nickelacycle can be an intermediate of nickel-catalyzed hydroacylation of alkenes. However, the first attempt at the expansion to a catalytic reaction failed due to the formation of stable isolable nickel dimer complex.…”