Ir-Catalyzed Asymmetric Total Syntheses of Bisdehydrotuberostemonine D, Putative Bisdehydrotuberostemonine E and Structural Revision of the Latter.

The first total syntheses of bisdehydrotuberostemonine D (8) and putative bisdehydrotuberostemonine E (9), two novel pyrrole Stemona alkaloids, along with the synthesis of bisdehydrotuberostemonine (3) have been completed in 12-13 steps. Our strategy harnesses the power of transition-metal-catalyzed reactions employing Ir, Ru, and Pd, in particular Ir-catalyzed asymmetric allylation of aldehydes, two distinct protocols recently developed by Carreira and Krische, respectively. The threefold use of Ir catalysis, first in the stereodivergent construction of two contiguous stereocenters at C (9,10) and then in rapid formation of the two γ-butyrolactone motifs, enabled the route's efficiency. Through this work, the originally assigned structure of bisdehydrotuberostemonine E (9) should be revised as 18α-bisdehydrotuberostemonine D (8*).