Recent progress in the synthesis of 1,2,3,4-tetrahydroquinolines

Many good synthetic methods for 1,2,3,4-tetrahydroquinolines bearing substituents on the heterocyclic ring have been recently developed. The nature, number and relative location of the substituents are the key parameters to consider before choosing a method. Recommended synthetic methods are summarized in the Table. Benzotriazole methodology is frequently the best method for making 3-monosubstituted 4-monosubstituted and 3,4-disubstituted tetrahydroquinolines. Substitution at the nitrogen atom and at the aromatic ring, not considered in this review, may also influence the choice of the optimum method.