Palladium(II)-Catalyzed Reductive Cyclization of N-Tosyl-Tethered 1,7-Enynes: Enantioselective Synthesis of 1,2,3,4-Tetrahydroquinolines

A novel Pd(II)-catalyzed reductive asymmetric cyclization of N-tosyl-tethered 1,7-enynes using ethanol as a hydrogen source is reported. This reaction provides facile ways for the synthesis of two types of 1,2,3,4-tetrahydroquinolines possessing a chiral quaternary carbon center in high yields with excellent enantioselectivities. The obtained products can also be converted to other chiral functionalized tetrahydroquinolines efficiently. The procedure involves a palladium catalyzed intramolecular hydropalladation/1,4-addition or beta-heteroatom elimination cascade process.