2 research outputs found
Double Palladium Catalyzed Reductive Cyclizations. Synthesis of 2,2′‑, 2,3′‑, and 3,3′-Bi‑1<i>H</i>‑indoles, Indolo[3,2‑<i>b</i>]indoles, and Indolo[2,3‑<i>b</i>]indoles
A palladium catalyzed, carbon monoxide
mediated, double reductive
cyclization of 1,4-, 1,3-, and 2,3-bisÂ(2-nitroaryl)-1,3-butaÂdienes
to afford 2,2′-, 2,3′-, and 3,3′-biindoles, respectively,
was developed. In contrast, reductive cyclizations of 1,2-bisÂ(2-nitroÂaryl)Âethenes
were nonselective, affording mixtures of monocyclized indoles, indoloÂ[3,2-<i>b</i>]Âindole, indoloÂ[1,2-<i>c</i>]Âquinazolin-6Â(5<i>H</i>)-ones, and 5,11-dihydro-6<i>H</i>-indoloÂ[3,2-<i>c</i>]Âquinolin-6-ones. Nonselective product formation
was also observed from reductive cyclization of 1,1-bisÂ(2-nitroÂaryl)Âethenes,
producing indoloÂ[2,3-<i>b</i>]Âindoles and indoloÂ[2,3-<i>c</i>]Âquinolin-6-ones. Carbon monoxide insertion to give
the carbonyl containing products was the major or sole reaction path
starting from 1,1- or 1,2-bisÂ(2-nitroÂaryl)Âethenes
Total Synthesis of the Tetracyclic Indole Alkaloid Ht-13‑B
An
expedient synthesis corroborating the proposed structure of
the tetracyclic indole alkaloid ht-13-B is presented. Key synthetic
steps include acyliminium ion allylation, a Mitsunobu reaction, a
palladium-catalyzed Stille–Kelly cross coupling reaction, and
a carbon monoxide-mediated palladium-catalyzed reductive <i>N</i>-heterocyclization. The chiral centers are ultimately derived from
commercially available <i>trans</i>-4-hydroxy-l-proline