Hydrozirconation of stannylacetylenes. Synthesis and reactions of ketene stannyl(telluro) acetals

Stannylacetylenes 7a-e react with Cp2Zr(H)Cl in THF at room temperature to give the alpha-zirconated vinylstannane intermediates 8a-e, which subsequently react with butyltellurenyl bromide (2.0 equiv) to give exclusively ketene stannyl(telluro) acetals 6a-e off configuration. Similar reactions were performed using phenylselenenyl bromide (2.0 equiv) as the electrophile, but a mixture of products was formed including the expected ketene stannyl(seleno) acetals 12. Otherwise, the use of 1.4 equiv of Cp2Zr(H)Cl and 1.0 equiv of PhSeBr results in the exclusive formation of 12, in good yields. Treatment of ketene stannyl(telluro) acetals with iodine or NBS followed by reductive dehalogenation results in the formation of 1-iodo-1-telluroalkenes 4a-e and 1-bromo-1-telluroalkenes 5a-e, respectively, with total retention of the configuration.