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

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 TMSCH═CH 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(TMSCH═CH 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 )-PhCH═C(Ph)CH( t Bu)OH, and ( Z )-1-iodo-4,4-dimethyl-1,2-diphenylpent-1-en-3-ol and ( Z )-PhCI═C(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.