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.
Supplementary materials
Supplementary File 1Supplementary File 2References and Notes
- Kathawal, F.G.; Copolla, G. M.; Schuster, H. F. Isoquinolines; The Chemistry of Heterocyclic Compounds; A series of Monographs; Vol. 38, Wiley & Sons: New York, 1990. [Google Scholar]
- Shamma, M. The Isoquinoline Alkaloids, Chemistry and Pharmacology; Academic Press: New York, 1972. [Google Scholar]
- Sample Availability: Commercially available.
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