Efficient Palladium-Catalyzed Aerobic Oxidative Carbocyclization to Seven-Membered Heterocycles.

Jie Liu,Jan‐E Bäckvall

doi:10.1002/chem.202004265

Abstract

The use of molecular oxygen in palladium‐catalyzed oxidation reactions is highly widespread in organic chemistry. However, the direct reoxidation of palladium by O2 is often kinetically unfavored, thus leading the deactivation of the palladium catalyst during the catalytic cycle. In the present work, we report a highly selective palladium‐catalyzed carbocyclization of bisallenes to seven‐membered heterocycles under atmospheric pressure of O2. The use of a homogenous hybrid catalyst (Co(salophen)‐HQ, HQ=hydroquinone) significantly promotes efficient electron transfer between the palladium catalyst and O2 through a low‐energy pathway. This aerobic oxidative transformation shows broad substrate scope and functional group compatibility and allowed the preparation of O‐containing seven‐membered rings in good yields in most cases.

Highlights

The use of molecular oxygen in palladium-catalyzed oxidation reactions is highly widespread in organic chemistry
Despite significant advances in palladium-catalyzed aerobic oxidations, a severe problem is that fast aggregation of palladium black from the active palladium species (Pd-H or Pd0) slows down and stops the homogenous reaction.[4]
A plethora of strategies to circumvent this oxidation problem have been reported, the development of highly active catalytic systems that enable mild Pd-catalyzed aerobic oxidations continues to be an important topic in this area

Summary

Introduction

The use of molecular oxygen in palladium-catalyzed oxidation reactions is highly widespread in organic chemistry. Strategies to improve the efficiency of palladium-catalyzed aerobic oxidative reactions. There is no example on the use of oxidative carbocyclization of bisallenes for the synthesis of useful organoboron molecules.[20] we report a general and efficient catalytic system for the synthesis of O-containing seven-membered heterocycles via cascade borylative carbocyclizations (Scheme 2 b).

Results

Conclusion