AlPhos and [(AlPhosPd)₂•COD] for Pd-Catalyzed Fluorination

Introduction

Fluorine containing aromatics (ArF) are desirable compounds with applications in medicinal chemistry and the agricultural industry. While Pd-catalyzed cross coupling has enabled the mild and general synthesis of aryl–C, –N, and –O bonds, the development of an analogous aryl–F bond forming process has lagged behind. In large part this is due to the challenging C–F reductive elimination from LPd^II(Ar)F intermediates.  However, a new ligand (AlPhos) and precatalyst [(AlPhosPd)₂•COD] developed by Buchwald and co-workers,¹ allows for regioselective and room temperature Ar–F bond formation from a variety of aryl triflates and aryl bromides.

Figure 1. AlPhos Structures

Advantages

Previous ligands used for this transformation resulted in the formation of regioisomeric aryl fluoride by-products complicating purification and isolation of the desired product, thus limiting the scope of the reaction. The highly active AlPhos (799718) ligated precatalyst (799726) is capable of operating at lower temperatures, which greatly reduces the amount of undesired regioisomer or eliminates it altogether. The activity of the developed catalyst is further highlighted by the room temperature fluorination of several activated substrates. Furthermore, the AlPhos ligated Pd(0) precatalyst (799726) was stable on the bench top as full catalytic activity was retained after being left open to the air for one week.

Representative Applications

Figure 2. AlPhos Representative Applications

Dedication

When a new ligand is discovered in the Buchwald lab, the person responsible for its invention has the opportunity to give it a name. AlPhos is dedicated to Albert B. Sather (the grandfather of Aaron C. Sather) for his continuous support and motivation.

Reference

1. Sather AC, Lee HG, De La Rosa VY, Yang Y, Müller P, Buchwald SL. 2015. A Fluorinated Ligand Enables Room-Temperature and Regioselective Pd-Catalyzed Fluorination of Aryl Triflates and Bromides. J. Am. Chem. Soc.. 137(41):13433-13438. https://doi.org/10.1021/jacs.5b09308