Studies on the Synthesis of Mavacurine-Type Indole Alkaloids. First Total Synthesis of (+/-)-2,7-Dihydropleiocarpamine

Article abstract of DOI:10.1021/jo00079a021

Closure of the six-membered C ring of pentacyclic mavacurine-type alkaloids from suitably substituted tetracyclic substructures embodying rings ABDE of these alkaloids, either by electrophilic cyclization upon the indole 3-position or by intramolecular alkylation of the piperidine nitrogen, failed.In contrast, 6a-homopleiocarpamine (45) has been synthesized from dithioacetal 42 by an electrophilic cyclization involving the closure of the seven-membered C ring.The first total synthesis of the alkaloid 2,7-dihydropleiocarpamine (58) has been achieved by photocyclization of the tetracyclic chloroacetamide 54 as the key step.The required tetracyclic ABDE ring systems were prepared by a straightforward sequence consisting of nucleophilic addition of a 1-indoleacetatic ester enolate to the γ position of a pyridinium salt, acid cyclization of the resulting 1,4-dihydropyridine, and final elaboration of the (E)-ethylidene substituent.An alternative synthesis of the tetracyclic alkaloid vinoxine (10a) is also reported.