Studies on the synthesis of strychnos indole alkaloids. A direct entry to 4-ethylidene-hexahydro-1,5-methanoazocino[4,3-b]indoles

✍ Scribed by Mercedes Alvarez; Rodolfo Lavilla; Joan Bosch

• Publisher: Elsevier Science
• Year: 1987
• Tongue: French
• Weight: 279 KB
• Volume: 28
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)96538-9

✦ Synopsis

A short, new route to the title tetracyclic substructure of Sf/cycho4 alkaloids, consisting in the nucleophilic attack of an ester a-anion to a pyridinium salt, acid-induced cyclization of the resultant 1,4_dihydropyridine, and stereospecific elaboration of the ethylidene substituent, is reported. The hexahydro-1,5-methanoazocino[4,3-6lindole system constitutes the tetracyclic framework of indole alkaloids uleine and dasycarpidone. This ring system possesses four of the five rings of pentacyclic Sfnychnu4 indole alkaloids. These alkaloids are characterized by an additional two-carbon chain connecting the piperidine nitrogen and the indole 3-position (E ring), an ethyl or ethylidene substituent at the 20-position, and, usually, a functionalized one-carbon substituent at the 16-position (biogenetic numbering'). We have recently reported a new synthetic entry to the pentacyclic ring skeleton of l . Rx'23 b.R:H CO*CH3