Nickel-Catalyzed Intramolecular Hydroalkenylation of Imines

Practical synthesis of allylic amines via nickel-catalysed multicomponent coupling of alkenes, aldehydes, and amides

Molecules with an allylic amine motif provide access to important building blocks and versatile applications of biologically relevant chemical space. The need for diverse allylic amines requires the development of increasingly general and modular multicomponent reactions for allylic amine synthesis. Herein, we report an efficient catalytic multicomponent coupling reaction of simple alkenes, aldehydes, and amides by combining nickel catalysis and Lewis acid catalysis, thus providing a practical, environmentally friendly, and modular protocol to build architecturally complex and functionally diverse allylic amines in a single step. The method is remarkably simple, shows broad functional-group tolerance, and facilitates the synthesis of drug-like allylic amines that are not readily accessible by other methods. The utilization of accessible starting materials and inexpensive Ni(ii) salt as the alternative precatalyst offers a significant practical advantage. In addition, the practicality of the process was also demonstrated in an efficient, gram-scale preparation of the prostaglandin agonist.

Our Voyage from Catalytic Cross-Hydroalkenylation to Transfer-Dehydroaromatization of Cyclic π-Systems: Reactivity and Selectivity Changes Enabled by NHC-Ni and NHC-Pd Hydride Equivalents

N-Heterocyclic carbene ligated transition-metal catalysts often show interesting properties and reactivity as compared to conventional ligand systems. In (NHC)Ni and (NHC)Pd hydrides, a dramatic reactivity changed from cross-hydroalkenylation to transfer-dehydroaromatization was observed under optimized conditions. This account summarizes our recent efforts and stories behind this serendipitous discovery. The mechanistic studies revealed that the keys to divert the desired reactivity are the differences in the olefin insertion selectivity and the hydrometallated species reactivity.

Synthesis of oxaboranes via nickel-catalyzed dearylative cyclocondensation

We report Ni-catalyzed dearylative cyclocondensation of aldehydes, alkynes, and triphenylborane. The reaction is initiated by oxidative cyclization of the aldehyde and alkyne coupling partners to generate an oxanickelacyclopentene which reacts with triphenylborane to form oxaboranes. This formal dearylative cyclocondensation reaction generates oxaboranes in moderate-to-high yields (47–99%) with high regioselectivities under mild reaction conditions. This approach represents a direct and modular synthesis of oxaboranes which are difficult to access using current methods. These oxaboranes are readily transformed into valuable building blocks for organic synthesis and an additional class of boron heterocycles. Selective homocoupling forms oxaboroles, oxidation generates aldol products, and reduction and arylation form substituted allylic alcohols.

Oxaboranes are prepared via a nickel-catalyzed dearylative cyclocondensation reaction in up to 99% yield and excellent regioselectivity. These oxaborane products can be further transformed into a variety of synthetically useful building blocks.