Reaction of Bicyclic Zirconacyclopentenes with Aldehydes and a Potential Pathway to Condensed 5-7-6(Ar) Ring Systems
Abstract
Bicyclic zirconacyclopentenes prepared by the reactions of 1,6- and 1,7-enynes with [Cp2ZrBu2] (Negishi reagent) reacted with a plethora of aldehydes (aryl, heteroaryl, alkyl, alpha,beta-unsaturated) by chemo-and stereoselective insertion into the sp(3) C-Zr bond to give the corresponding oxazirconacycloheptenes. Subsequent hydrolysis or halogenolysis provided the corresponding alcohols 4 (31-74% isolated yields) or halides 10 (35-50% isolated yields).
The oxazirconacycloheptenes prepared by the insertion of 2-iodobenzaldehyde were also subjected to intramolecular coupling in the presence of CuCl and additives, and compounds possessing the condensed 5-7-6(aryl) ring system were obtained in reasonable isolated yields (32-46%). The same ring system was also prepared by the Pd-catalyzed coupling of dihalo derivatives 10 (38-42% H-1 NMR yields).
Moreover, the mechanism of the unproductive side-reaction leading to ketones during the reaction with CuCl was elucidated.