Studies on the syntheses of heterocyclic compounds. Part 876. The chiral total synthesis of brevianamide E and deoxybrevianamide E
The chiral total synthesis of brevianamide E (1) and deoxybrevianamide E (2) starting from L-proline is described. Condensation of 2-(1,1-dimethylallyl)-3-dimethylaminomethylindole (3) and (–)-methyl 1,4-dioxoperhydropyrrolo[1,2-a]pyrazine-3-carboxylate (7) derived from L-proline followed by demethoxycarbonylation gave (–)-deoxybrevianamide E (2) and its epimer (10). Photo-oxygenations of (2) and (10) formed (–)-brevianamide E (14) and its three stereoisomers (15), (16), and (17). The absolute stereochemistry of brevianamide E (14) was determined as 4aS,5aR,10aS,11aS by this synthesis.