1999 Volume 47 Issue 9 Pages 1269-1275
A synthesis of 1, 2, 3, 4-tetrahydroquinolines (TQs) 13 with two and three methoxyl groups on the benzene ring, was achieved via intramolecular cyclization of N-aryl-N-[(phenylsulfinyl)propyl]formamides 7 utilizing the Pummerer reaction as a key step. The reaction was carried out by using trifluoroacetic anhydride (TFAA)(method A) or TFAA-BF3·Et2O (method B). The cyclization to 4-PhSTQs 8 proceeded effectively when the reaction center at the benzene ring was electronically activated by a methoxyl group. In the reaction of sulfoxide 7e having two OMe groups in the ortho- and para-positions, a different cyclization reaction leading to 1, 5-benzothiazepine derivative 9 was observed, indicating that the high uncleophilicity of the benzene ring caused the unexpected reaction prior to cyclization to 4-PhSTQs 8. This route starting from methoxyanilines provides an efficient and convenient method of TQ synthesis.
