Synthesis of vinca alkaloids and related compounds LXXXIII unexpected Pictet-Spengler side-reaction

✍ Scribed by Lajos Szabó; Éva Szentirmay; Eszter Baitz-Gács; György Kalaus; Csaba Szántay

• Publisher: Elsevier Science
• Year: 1997
• Tongue: French
• Weight: 118 KB
• Volume: 38
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(96)02230-7

✦ Synopsis

In the initial stage of the synthesis of the eburnane-type alkaloids ( e.g. vincamine ) the condensation reaction of tryptamine (1) either with diearboxylic acid aldehyde 2a , or with diester aldehyde 2e has frequently been used. As a result of this Pictet-Spengler-type reaction, followed by ring-forming internal acylation, the desired pentaeyelie (3) or tetracyclic (4) products were obtained in good yields z.

We should like to disclose our observation concerning an unexpected variation of this reaction. If instead of 2a or 2c the half-ester of the corresponding acid 2d ~ was used, under the same reaction conditions the dimeric product, naphthyridine derivative 5* was isolated in 24% yield, in addition to 26,9 % of the two additional isomeric tryptamides ( aa 5 20,2 % , tlb 6 6,7 % ). The new reagent 2d 3 was prepared by partial hydrolysis of 2c ~. The stereostructure of 5 was proved by NeE measurements.