Nickel(0)-Catalyzed Formation of Oxaaluminacyclopentenes via an Oxanickelacyclopentene Key Intermediate: Me₂AlOTf-Assisted Oxidative Cyclization of an Aldehyde and an Alkyne with Nickel(0)

Abstract

The use of Me 2 AlOTf as an additive allowed the oxidative cyclization of pivalaldehyde and diphenylacetylene with nickel(0) in the presence of PCy 3 to give an oxanickelacyclopentene, the structure of which was unambiguously determined by means of X-ray diffraction study. In the presence of TMSCHdCH 2 , treatment of the oxanickelacyclopentene with an equimolar amount of AlMe 3 quantitatively gave an oxaaluminacyclopentene with simultaneous generation of ethane and the Ni(0) species (PCy 3 )Ni-(TMSCHdCH 2 ) 2 . The oxaaluminacyclopentene was a suitable precursor for the preparation of allylic alcohol derivatives due to its reactive Al-C bond, and treatment with HCl or I 2 afforded (E )-4,4-dimethyl-1,2-diphenylpent-1-en-3-ol and (E)-PhCHdC(Ph)CH( t Bu)OH, and (Z)-1-iodo-4,4-dimethyl-1,2-diphenylpent-1-en-3-ol and (Z)-PhCIdC(Ph)CH( t Bu)OH, respectively, in excellent yield. This sequential reaction was successfully expanded to a Ni(0)-catalyzed three-component cyclocondensation reaction of an aldehyde, an alkyne, and AlMe 3 that gave the corresponding oxaaluminacyclopentenes in moderate to good yields. The scope of substrates and the mechanism of the reaction are also reported.

The roles of Lewis acidic additives in organotransition metal catalysis

“…C-H bond activation. Similar catalysts are useful for catalytic C-H functionalisation, including hydroarylation of alkenes and/or alkynes using pyridines, 29,30 pyridones, 31 benzamides, 32 and sulfonylarenes, 33 as well as the alkenylation of C-H bonds in aldehydes 34 and formamides. 35,36 Regio-and chemodivergent hydroarylation of alkynes is observed as a function of ligand and Lewis acid identity, and demonstrative examples are shown in Scheme 7.…”

[3+2] Cycloaddition Reaction of Cyclopropyl Ketones with Alkynes Catalyzed by Nickel/Dimethylaluminum Chloride

“…The coordination of the unsaturated bonds of cyclopropyl ketones and alkynes occurs to give the h 2 :h 2 -coordinated nickel complex A. Organoaluminum reagents might enhance the coordination ability of cyclopropyl ketones toward the nickel(0) center by the coordination of the oxygen atom of the carbonyl group. [21] The oxidative addition of the proximal carbon-carbon bond of the cyclopropyl ketones to nickel(0) occurs to give the nickelacyclobutane intermediate B.…”

“…Recently, we reported the isolation of oxa-nickelacyclopentene by the oxidative cyclization of an alkyne and an aldehyde with nickel(0) promoted by Me 2 AlOTf, in which the coordination of one oxygen atom of a OTf group to a nickel(II) center was observed. [21] Thus, the substituent X of organoaluminum reagents such as Me, [22] Cl, [23] and OAc groups would also coordinate toward the nickel(II) center to stabilize the reaction intermediates by forming a chelate structure. The insertion of an alkyne into the carbon-nickel bond of B affords the nickelacyclohexene intermediate C. The experimental results of stoichiometric reactions with 7 and very rapid formation of 6 by the reaction of 5 with Me 2 AlCl suggest that the generation of the intermediate D is unlikely.…”

[3+2] Cycloaddition Reaction of Cyclopropyl Ketones with Alkynes Catalyzed by Nickel/Dimethylaluminum Chloride

“…The coordination of the unsaturated bonds of cyclopropyl ketones and alkynes occurs to give the η 2 :η 2 ‐coordinated nickel complex A . Organoaluminum reagents might enhance the coordination ability of cyclopropyl ketones toward the nickel(0) center by the coordination of the oxygen atom of the carbonyl group 21. The oxidative addition of the proximal carbon–carbon bond of the cyclopropyl ketones to nickel(0) occurs to give the nickelacyclobutane intermediate B .…”

“…The oxidative addition of the proximal carbon–carbon bond of the cyclopropyl ketones to nickel(0) occurs to give the nickelacyclobutane intermediate B . Recently, we reported the isolation of oxa‐nickelacyclopentene by the oxidative cyclization of an alkyne and an aldehyde with nickel(0) promoted by Me 2 AlOTf, in which the coordination of one oxygen atom of a OTf group to a nickel(II) center was observed 21. Thus, the substituent X of organoaluminum reagents such as Me,22 Cl,23 and OAc groups would also coordinate toward the nickel(II) center to stabilize the reaction intermediates by forming a chelate structure.…”