Zirconacyclopentenes synthesis

The most versatile synthesis involves the transmetallation of a zirconiacyclopentadiene231,232 with a tin halide under catalysis with CuCl233 (and an equivalent reaction occurs with other halides of other elements of Groups 13, 14, 15, and 16) (Equation (77)). Stannacyclopentenes can be prepared by analogous reactions of zirconacyclopentenes.233... 

The synthetic potential of organozirconocenes is greatly expanded by their easy transformation into other organometallics. Therefore, transmetalation-based approaches to cyclopropane synthesis have been reported. The reaction of zirconacyclopentene with phthaloyl chloride in the presence of CuCl was used for the preparation of cyclopropylenolate derivatives in moderate yields (Scheme 29) [39]. 

Reductive cleavage of zirconacyclopentene was utilized for the synthesis of various zirconacycles by C-C bond cleavage/formation sequences [99]. 

The development of new methods to synthesize molecules with multiple stereo-genic centers in one flask is very important in organic synthesis [13]. Ftmctionalized allenes are of great interest since they serve as versatile synthetic intermediates in many asymmetric syntheses. Under mild conditions, stereoselective synthesis of p-hydroxyallenes was obtained via aldehyde addition to a-alkenyl-substimted zirconacyclopentenes (Scheme 2). The product 5 has two contiguous stereogenic centers and an adjacent axial chirality. 

Zirconacyclopentene 1-5 could also be applied in synthetic reaction (Scheme 1.8). For example, in the presence of CuCl and iodine, oxidative demetallation of 1-5 gives cyclobutene derivatives [34]. Reaction of 1-5 with acid chloride gives tri-subslimted cyclopentadiene derivatives [35]. This research group also reported zirconocene-mediated cyclization of alkyne, ethylene, and two molecules of aldehyde toward synthesis of 2-alkenyl tetrahydrofuran [36]. 

Ren S, Chan HS, Xie Z (2009) Synthesis structure and reactivity of zirconacyclopentene incorporating a carboranyl unit. J Am Chem Soc 131 3862-3863... 

Cyclic gem-metallozirconocene compounds such as a-lithiated zirconacyclopentadienes, a-stannyl or gallio-zirconacyclopentenes, and a,o -bis(trimethylstannyl) zirconacyclopentadienes have been prepared (Fig. 3) [21-25]. These multifunctionalized zirconacycles can be expected to have useful applications in organic synthesis. 

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