Subject hydrozirconation

The hydrozirconation of alkynes by Cp2ZrHCl has been studied in detail . The addition of Zr-H is uniquely cis, and in 1-alkynes the zirconium attaches to the terminal carbon atom with high regioselectivity ( 98%). The direction of cis-fi addition of Zr-H to internal alkynes is sensitive to the steric bulk of the two substituents of the alkyne and, in the absence of excess Zr-H, is subject to kinetic control. The presence of excess Zr-H results in rapid equilibration of the initial mixture. The results of some hydrozirconations of internal alkynes are shown in Table H. 

Hydrozirconation of functionalized alkyne 8 in CH2C32 with the Schwartz reagent followed by in situ transmetallation to Me2Zn and addition of N-diphenyl-phosphinoylimine 15 provides the functionalized trans-aminocydopropane 16 in 60% yield [15]. The cydopropane formation can be rationalized by the formation of a transient zinc-carbenoid species from CH2CI2, which subjected the intermediate allylic amine derivative to an efficient Simmons-Smith-type cydopropanation. 

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