Search

An efficient synthesis of bisbenzopyrones by a N-heterocyclic carbene (NHC)-catalyzed intramolecular hydroacylation-Stetter reaction cascade has been developed. A series of symmetrical and unsymmetrical bisbenzopyrones were obtained with good to excellent yields. Bisbenzopyran-4-ol was synthesized efficiently. [ABSTRACT FROM AUTHOR]

Dimethylzirconocene reacts with 2 molar equiv of the persistent radical TEMPO to give the Cp2Zr(Me)OTMP complex 12 with formation of TEMPOMe. Methyl anion abstraction from 12 with B(C6F5)3 generates the [Cp2ZrOTMP+] cation 13 (with the [MeB(C6F5)3]- anion) that undergoes a typical intramolecular frustrated Zr+/N Lewis pair (FLP) reaction with phenylacetylene. With PtBu3 it reacts as an intermolecular Zr+/P FLP trapping carbon dioxide. Complex 12 reacts with HB(C6F5)2 also by methyl anion abstraction to form the μ-H bridged tight ion pair Cp2ZrOTMP(μ-H)BMe(C6F5)2 (19). It serves as a Cp2Zr(H)OTMP zirconocene hydride source in the reaction with CO2, giving the respective [Zr](μ-formate)[B] complex 23. With carbon monoxide it forms the Zr-(η²-acetaldehyde)[B] complex 30 by transfer of both the hydride and the methyl anion from the Zr/B pair to the carbon atom of the CO molecule. [ABSTRACT FROM AUTHOR]