Samarium Diiodide-Induced Diastereoselective Synthesis of Hexahydro-quinoline Derivatives

Samarium diiodide-induced cyclization of aniline derivatives 5, 9, 12, 14, and 16 afforded hexahydroquinolines such as 6, 10, 13, 15, and 17 in moderate to good yields and excellent diastereoselectivities. Phenol was found to be a surprisingly effective proton source in some of these samarium-ketyl cyclizations. The influence of different substituents at nitrogen as well as at the aromatic ring of the aniline moiety was studied. Whereas para-donor-substituted aniline derivatives 19 and 21 provided the expected products 20 and 22, the corresponding para-cyano derivatives 23 and 26 took an alternative pathway. Ipso-substitution involving spiro intermediates 29 resulted in formation of rearranged products 24 and 28.