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‐ketoacids with hydrazines for selective access to hexahydropyridazines and tetrahydropyridazin‐3(2H)‐ones has been developed. The combination of B(C6F5)3 and Et3SiH allows for synthesis of various hexahydropyridazines and tetrahydropyridazin‐3(2H)‐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(C6F5)2 and a binaphthyl‐based chiral diene and PhMe2SiH, 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.