Tandem titanocene-mediated

GansSuer et al. studied the tandem titanocene-mediated cyclization/inter-molecular addition to Michael acceptors [132]. After treatment with t-butyl acrylate in the presence of Zn, collidine hydrochloride and catalytic amounts of titanocene [133], epoxide 143 yielded the desired bicycUc product 144 in reasonable yield and high diastereoselectivity (Scheme 46). Remarkably, alkyne 145 led to the first example of an intermolecular addition involving a vinylic radical. The success of this reaction was attributed by the authors... 

Abstract This review presents a description of the C-C bond-forming reactions that have emerged in the field of titanocene mediated or catalyzed epoxide opening over the last 5 years or so. The powerful tandem sequences for polycylization will be especially emphasized. 

Barrero, Oltra and coworkers reported on the use of epoxygeranyl acetate in titanocene-mediated cyclizations and found that the termination of the reaction took place via a /i-hydride elimination after trapping of the radical by the second equivalent of Cp2TiCr [94,95]. This finding together with Takahashi s tandem cyclization [96] (see below) marks the first example of extremely interesting developments in epoxypolyene cyclizations via radicals that are discussed separately in the following section. 

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