Zirconium-catalyzed and zirconium-promoted cyclization reactions of non-conjugated dienes with alkylmagnesium halides to give cycloalkylmethylmagnesium derivatives

The stoichiometric reaction of certain non-conjugated dienes with n-Bu2ZrCp3 provides the corresponding zirconabicycles, such as trans-3-bis( cyclopentadienyl) zirconabicyclo [3.3.0] octane, that can be fully characterized by spectroscopic means. Their treatment with EtMgBr or n-BuMgCl in THF gives The corresponding monocyclic monomagnesium derivatives along with the corresponding alkene-ZrCp2 derivatives in high yields. In cases where the Grignard reagent is either sterically hindered or lacking P-HI little or no reaction may occur, although some, e.g., s-BuMgCl, react, albeit slowly, to give the expected products in high yields. In cases where either a Grignard reagent in diethyl ether or a dialkylmagnesium (irrespective of solvent) is used, the major product is the corresponding dimagnesio derivative. A couple of intramolecular transmetallation paths are proposed for these cases. The Cp2ZrCl2-catalyzed reaction of 1,6-heptadiene with EtMgBr fails to induce the desired bicyclization-ring opening sequence to give the corresponding monocyclic monomagnesium derivatives. On the other hand, the corresponding reaction with n-BuMgBr does proceed as desired to give the monocyclic monomagnesium product which contains a minor amount of the corresponding exo-methylene derivative. Only traces, if any, of the corresponding dimagnesium derivatives reported to be the major products in Et2O are formed. This procedure has been applied to catalytically convert several other dienes, i.e., (E)-1-phenyl-1,6-heptadiene, 2,4,4-trimethyl-1,6-heptadiene, diallyl (benzyl) amine, 1,7-octadiene and 1,2-diallylbenzene, into the corresponding monocyclized compounds in moderate to excellent combined yields. (C) 1998 Elsevier Science S.A. All rights reserved.