Biomimetic Total Syntheses of (−)-Leucoridines A and C through the Dimerization of (−)-Dihydrovalparicine.

Concise biomimetic syntheses of the Strychnos-Strychnos-type bis-indole alkaloids (−)-leucoridine A ( 1) and C ( 2) were accomplished through the biomimetic dimerization of (−)-dihydrovalparicine ( 3). En route to 3, the known alkaloids (+)-geissoschizoline ( 8) and (−)-dehydrogeissoschizoline ( 10) were also prepared. DFT calculations were employed to elucidate the mechanism, which favors a stepwise aza-Michael/spirocyclization sequence over the alternate hetero-Diels-Alder cycloaddition reaction. [ABSTRACT FROM AUTHOR]