Total Synthesis of Dictyodendrins by the Gold‐Catalyzed Cascade Cyclization of Conjugated Diynes with Pyrroles

Abstract

In total and formal syntheses of dictyodendrins B, C, E, and F, the key step involved the direct construction of the pyrrolo[2,3‐c]carbazole core by the gold‐catalyzed annulation of a conjugated diyne with a pyrrole to form three bonds and two aromatic rings. The subsequent introduction of substituents at the C1 (Suzuki–Miyaura coupling), C2 (addition to an aldehyde), N3 (alkylation), and C5 positions (Ullman coupling) provided divergent access to dictyodendrins.

Silver‐Catalyzed Carbocyclization of Azide‐Tethered Alkynes: Expeditious Synthesis of Polysubstituted Quinolines

“…The molecular structure of 9 t was inferred from X-ray diffraction analysis of its analogue 9 u. [19] Based on these results and the reported literature, [9][10][11][12][13][14][15] a tentative reaction mechanism was proposed for the generation of polysubstituted quinolines, which is shown in Scheme 7. Initially, 6-endo-dig cyclization of the Ag(I)-activated alkyne moiety with tethered azide formed intermediate I, which further led to aimino silver carbene species II after extrusion of N 2 .…”

“…To our delight, the yields of 3 a were improved dramatically when the reaction was promoted by silver catalysts. Examination of different silver catalysts at different temperatures (entry [8][9][10][11][12][13] revealed that AgSbF 6 gave the best yield at 20 8C (entry 11, 85% yield). The molecular structure of 3 a was inferred from X-ray diffraction analysis of its analogue 3 n. [19] With the optimal reaction conditions established, the substrate scope of azide alkynes with various substituted aromatic nucleus was investigated.…”

“…[8] Recently, Toste and coworkers reported the first gold(I)-catalyzed intramolecular acetylenic schmidt reaction for the direct construction of pyrrole frameworks (Scheme 1a). [9] Later, this useful method was further studied by Zhang, [10] Gagosz, [11] Ohno, [12] Ye, [13] us, [14] and others [15] for the preparation of pyrrole or indole derivatives with structural diversity (Scheme 1b). Inspired by those advances and as the continuation of our interest in alkyne bifunctionalization, [16] we envisioned that a general approach for the construction of quinoline frameworks could be realized via an 6-endo-dig azide-yne cyclization if an electron-deficient carbonyl group was installed between the alkyne and azide species (Scheme 1c).…”

Copper‐Catalyzed Successive C−C bond formations on Indoles or Pyrrole: A Convergent Synthesis of Symmetric and Unsymmetric Hydroxyl Substituted N‐H Carbazoles

“…Naturally, as we envisioned in Scheme , we decided to test the more challenging pyrrole substrate in order to gauge the full capability of this interesting method ,. We found that under slightly modified reaction conditions, the synthetically valuable symmetric densely substituted and hydroxyl containing carbazoles were formed in moderate yields (Table ).…”

Gold‐Catalyzed Dual Annulation of Homopropargyl Alcohols with Nitrones: Synthesis of Tetrahydropyrano[4,3‐b]indole Scaffolds

“…[4] Among these approaches, the gold-catalyzed alkyne cyclization with tethered azide, which is firstly reported by Toste and coworkers, [5,6] has provided general access to Nheterocycles via corresponding α-iminocarbene intermediates under a mild and neutral conditions (Scheme 1a). Later, this useful method has been further studied by Zhang, [7] Gagosz, [8] Ohno, [9] Ye, [10] us, [11] and others [12] for the preparation of pyrrole or indole derivatives with structural diversity.…”