Borane‐Catalyzed Selective Transformation of Levulinic Acid and Hydrazines into Hexahydropyridazines and Tetrahydropyridazin‐3(2H)‐ones Using Hydrosilane

Abstract Borane‐catalyzed one‐pot tandem cyclization/hydrosilylation of levulinic acid and other γ‐keto acids with hydrazines for selective access to hexahydropyridazines and tetrahydropyridazin‐3(2 H )‐ones has been developed. The combination of B(C 6 F 5 ) 3 and Et 3 SiH allows for synthesis of various hexahydropyridazines and tetrahydropyridazin‐3(2 H )‐ones in 67–97% yields with tolerance towards various functional groups and easy scale‐up. This reaction can be rendered enantioselective by using a chiral borane catalyst generated in situ from HB(C 6 F 5 ) 2 and a binaphthyl‐based chiral diene and PhMe 2 SiH, affording the target products in 70–92% yields with up to >99% ee. The judicious choice of borane catalyst and hydrosilane reductant proves to be critical for catalysis. Mechanistic investigations elucidate the catalytic pathway.