1,2,3,4-Tetrahydroisoquinoline

Molecules 1997, 2, M25

1,2,3,4-Tetrahydroisoquinoline from Acid Catalysed Cyclisation of N,N'-Dibenzylethylenediamine

N. Peerzada

Faculty of Science, Northern Territory University, Casuarina, Darwin, Northern, Territory, Australia 9090. Tel: 61-8-89466360, Fax :61-8-89466847, Email: [email protected]

Received: 8 August 1997 / Published: 12 August 1997

1,2,3,4-Tetrahydroisoquinolines have been traditionally prepared by the Bischler-Napieralski, Pictet-Gams, Pictet-Spengler, Pomeranz-Fritsch reactions and various Friedel-Crafts cyclization procedures of N-(haloalkyl)aryl derivatives [1]. These reactions have often been used in the total synthesis of isoquinoline alkaloids [2]. Since the starting compound was commercially available, the present reaction was carried out on a larger scale to afford clean product 1 in high yield.

The decomposition of dibenzylethylenediamine (24g, 0.1mole) was carried out in a Claisen distillation equipment at 240 deg.C and 20 mmHg. The catalyst was added as 48% hydrobromic acid (1.5mL). The heating was continued until 91% of distillate was obtained. The distillate on fractional distillation (45 deg.C at 2mmHg) gave 1,2,3,4-tetrahydroisoquinoline (1) (9.6g, 72%), benzylamine (2.8g, 26%) and some residue which was mainly unchanged diamine.

The tetrahydroisoquinoline (1) prepared was further characterized by comparisons (ir and nmr) with authentic specimen.

B.p. 45 deg.C at 2mmHg.

References and Notes

1. Kathawal, F.G.;Copolla, G. M and Schuster, H. F. Isoquinolines, The Chemistry of Heterocyclic Compounds. A series of Monographs, Vol. 38. Wiley & Sons: New York, 1990.

2. Shamma, M. The Isoquinoline Alkaloids, Chemistry and Pharmacology, Academic Press: New York, 1972.

Sample Availability: Commercially available.