p-Cresol-Enabled Nickel-Catalyzed Intermolecular Redox-Economical Coupling of Allyl Alcohols with Alkynes through oxa-Nickelacycle

Dehydrogenative [4 + 2] Annulation of 1-Indanones with Alkynes Enabled by In-Situ-Generated Nickel Hydride

“…Based on all the above-mentioned results and previous reports, ,− a plausible mechanism is depicted in Scheme . The reactions commence with a Ni(II)-mediated 1-indanone 1a desaturation to generate an α,β-unsaturated carbonyl intermediate B and form a nickel hydride species.…”

“…19 Moreover, Zhou and co-workers 20 elegantly reported a strategy of generating nickel-hydride species from a Ni−Brønsted acid cocatalyst, which lately was demonstrated as a robust catalyst in the coupling reaction between alkyne and allylic alcohols by Wang and co-workers (Scheme 2c). 21 Inspired by these two works, we envisaged that the combination of nickel-catalyzed desaturation of 1-indanones with a subsequent coupling with alkyne might provide direct access to benzo[a]fluorenone scaffolds via a formal dehydrogenative [4 + 2] addition (Scheme 2d). However, the implementation of the cascade dehydrogenation/cycloaddition of 1-indanones with alkynes to produce benzo[a]fluorenones has been largely restricted by some key challenges, such as (a) the rapid generation of nickel hydride species from the desaturation of 1-indanones is required, (b) nickelacycle should be formed to cyclize the six-membered ring of the product, (c) the regioselectivity issue should be well addressed to obtain reasonable reaction yield.…”

“…Recently, a remarkable breakthrough has been achieved by Newhouse in the nickel-catalyzed α,β-desaturation of carbonyl compounds in the presence of mild oxidants via an in-situ-generated nickel hydride intermediate (Scheme b) . Moreover, Zhou and co-workers elegantly reported a strategy of generating nickel-hydride species from a Ni–Brønsted acid cocatalyst, which lately was demonstrated as a robust catalyst in the coupling reaction between alkyne and allylic alcohols by Wang and co-workers (Scheme c) . Inspired by these two works, we envisaged that the combination of nickel-catalyzed desaturation of 1-indanones with a subsequent coupling with alkyne might provide direct access to benzo[ a ]fluorenone scaffolds via a formal dehydrogenative [4 + 2] addition (Scheme d).…”

Ni-Catalyzed Diastereoconvergent Intramolecular Alkene–Aldehyde Reductive Coupling: A Route to syn-Chromanols

“…The involvement of a Ni−H mediated reaction was ruled out by subjecting 1a to the conditions known to promote Ni− H intermediacy. 15 The reaction failed to start under these conditions. Then, to determine whether the silane was the sole hydride source, we performed the reaction with Ph 2 SiD 2 (98%-D) under standard conditions.…”

“…The reaction provided 2a (37%) and 2b (34%), along with 10 in 24% yield, confirming the involvement of a Ni 0 active catalyst (Scheme a). The involvement of a Ni–H mediated reaction was ruled out by subjecting 1a to the conditions known to promote Ni–H intermediacy . The reaction failed to start under these conditions.…”