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 Me2AlOTf as an additive allowed the oxidative cyclization of pivalaldehyde and diphenylacetylene with nickel(0) in the presence of PCy3 to give an oxanickelacyclopentene, the structure of which was unambiguously determined by means of X-ray diffraction study. In the presence of TMSCH═CH2, treatment of the oxanickelacyclopentene with an equimolar amount of AlMe3 quantitatively gave an oxaaluminacyclopentene with simultaneous generation of ethane and the Ni(0) species (PCy3)Ni(TMSCH═CH2)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 I2 afforded (E)-4,4-dimethyl-1,2-diphenylpent-1-en-3-ol and (E)-PhCH═C(Ph)CH(tBu)OH, and (Z)-1-iodo-4,4-dimethyl-1,2-diphenylpent-1-en-3-ol and (Z)-PhCI═C(Ph)CH(tBu)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 AlMe3 that gave the corresponding oxaaluminacyclopentenes in moderate to good yields. The scope of substrates and the mechanism of the reaction are also reported.