| Abstract
| - The total syntheses of β-carboline alkaloids, (R)-(−)-pyridindolols (1, 5, and 6) are described. Thetwo key steps involved are (1) a thermal electrocyclic reaction of the 3-alkenylindole-2-aldoxime10 and (2) a thermal cyclization of 3-alkynylindole-2-aldoxime 11 to construct the β-carbolineN-oxides 8, which upon heating with acetic anhydride and sequential treatment with trifluoromethanesulfonic anhydride gave the triflates 18. The Stille coupling reaction of 18 withvinylstannane, followed by cleavage of MOM ether, afforded the 1-ethenyl-3-hydroxymethyl-β-carboline (7a). Subsequent acetylation of 7a yielded the acetate 7b, which was subjected to theSharpless asymmetric 1,2-dihydroxylation by AD-mix-β to produce (R)-(−)-pyridindolol K2 (6).Selective acetylation of 6 was effected by Ac2O and collidine to form (R)-(−)-pyridindolol K1 (5). Bycontrast, hydrolysis of 6 provided (R)-(−)-pyridindolol (1).
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