A Versatile Route to Unstable Diazo Compounds via Oxadiazolines and their Use in Aryl–Alkyl Cross‐Coupling Reactions

Coupling of readily available boronic acids and diazo compounds has emerged recently as a powerful metal‐free carbon–carbon bond forming method. However, the difficulty in forming the unstable diazo compound partner in a mild fashion has hitherto limited their general use and the scope of the transformation. Here, we report the application of oxadiazolines as precursors for the generation of an unstable family of diazo compounds using flow UV photolysis and their first use in divergent protodeboronative and oxidative C(sp²)−C(sp³) cross‐coupling processes, with excellent functional‐group tolerance.     

Palladium‐Catalyzed Catellani ortho‐Acylation Reaction: An Efficient and Regiospecific Synthesis of Diaryl Ketones

A palladium‐catalyzed, norbornene‐mediated Catellani ortho‐acylation reaction was developed by the use of either acyl chlorides or acid anhydrides as acylation reagents. The addition of more than a stoichiometric amount of H₂O is crucial for this transformation when acid chlorides are used, and kinetic studies indicate that the active acylation reagent is possibly an acid anhydride.     

Pd‐PEPPSI‐IHeptCl: A General‐Purpose,Highly Reactive Catalyst for the Selective Coupling of Secondary Alkyl Organozincs

Dichloro[1,3‐bis(2,6‐di‐4‐heptylphenyl)imidazol‐2‐ylidene](3‐chloropyridyl)palladium(II) (Pd‐PEPPSI‐IHept^Cl), a new, very bulky yet flexible Pd–N‐heterocyclic carbene (NHC) complex has been evaluated in the cross‐coupling of secondary alkylzinc reactants with a wide variety of oxidative addition partners in high yields and excellent selectivity. The desired, direct reductive elimination branched products were obtained with no sign of migratory insertion across electron‐rich and electron‐poor aromatics and all forms of heteroaromatics (five and six membered). Impressively, there is no impact of substituents at the site of reductive elimination (i.e., ortho or even di‐ortho), which has not yet been demonstrated by another catalyst system to date.     

The Lightest Element Phosphoranylidene: NHC‐Supported Cyclic Borylidene–Phosphorane with Significant B=P Character

A borylidene–phosphorane, the lightest phosphoranylidene, which is stabilized by an N ‐heterocyclic carbene ligand, was synthesized and fully characterized. Experimental electron density analysis and DFT calculations indicate an enhanced ylene character (rather than an ylide character) with an exceptionally strong B→P π‐back bonding related to the less electronegative boron compared to phosphorus.