Biomimetic construction of the tetracyclic ring system of ngouniensine

2-Cyanotetrahydropyridine 9, bearing an indole-2-acetate moiety, was envisaged as a model synthetic equivalent of the dihydropyridinium cations A, which have been proposed as common biogenetic intermediates to both ngouniensine and Strychnos indole alkaloids. Lewis acid-promoted cyclization of the O-silyl ketene acetal derived from 9 led to the ngouniensine-type derivative 11. (C) 1999 Elsevier Science Ltd. All rights reserved.