Synthese der Spermidin‐Alkaloide (±)‐Inandenin‐10‐ol, Inandenin‐10‐on und (±)‐Oncinotin

Abstract

Syntheses of the Spermidine Alkaloids (±)‐Inandenin‐10‐ol, Inandenin‐10‐one, and (±)‐OncinotineNew syntheses of the title compounds using two‐ring‐enlargement reactions are described. Starting from the aldehyde 1, the corresponding 4′‐aza derivative 15 could be obtained by reductive amination with the appropriate and protected spermidine derivative 14 (Scheme 4). Enlargement of the carbocyclic ring in 15 by five members gave, after further transformations, the hydroxylactam 18. Transamidation of 18, the second ring‐enlargement step, led to (±)‐inandenin‐10‐ol (7;22.9% overall yield) and, after oxidation, to inandenin‐10‐one (8; 22.5%, overall yield). (±)‐Oncinotine 6 was synthesized by two pathways (Scheme 6): protection of the terminal NH2 group by treatment with the Nefkens reagent and replacement of the OH group by Cl gave 24, which by thermal transamidation followed by direct ring closure led to the oncinotine derivative 26. The same intermediate could be obtained in higher yield via 28 by oxidation and protection of 18 followed by transamidation and reductive ring closure. Treatment of 26 with hydrazine finally gave (±)‐oncinotine 6 in 15.9% overall yield.