Direct synthesis of aryl-annulated [c]carbazoles by gold(i)-catalysed cascade reaction of azide-diynes and arenes

Abstract

The gold-catalysed annulation of conjugated alkynes bearing an azido group with arenes gave annulated [c]carbazoles.

Recent Advances in Construction of Polycyclic Natural Product Scaffolds via One-Pot Reactions Involving Alkyne Annulation

“…Fortunately, a substrate with alkoxyl substituents reacts well with improved regioselectivity to give a product suitable for divergent syntheses of dictyodendrins B, C, E, and F. The pyrrolo[3,2-c]carbazole isomers, which are unwanted byproducts in target-oriented syntheses, would be rather valuable in diverse-oriented syntheses, as they can enrich the skeleton diversity via realignment of privileged substructures of natural products. The same group (Kawada et al, 2018) further extended the strategy to other substrates to synthesize a library of benzo[c]carbazoles and indolo[2,3-c]carbazoles, which may be useful for development of organic materials.…”

Total Synthesis of Dictyodendrins A–F by the Gold‐Catalyzed Cascade Cyclization of Conjugated Diyne with Pyrrole

“…We recently showed that treatment of diyne 20 a and N-Boc-pyrrole 21 a with [BrettPhosAuSbF 6 ] [36] (5 mol %) in dichloroethane (DCE) at 80 8C proceeded with high regioselectivity to afford the desired pyrrolo[2,3-c]carbazole (58 %y ield, 23 a/23'a = 95:5). [24] Therefore, these optimized conditions for 20 a were applied to conjugated diynes 29 a-c bearing an oxygen functional group.T he reaction of 29 a bearing methoxy (R 1 = OMe) and tert-butoxy groups (R 2 = OtBu) showed slightly decreased regioselectivity (28 a/28'a = 84:16) with an improved combined yield (79 %). In contrast, 29 b (R 2 = OMs) and 29 c (R 2 = OBn) gave the annulation products with relatively low regioselectivities (28/28' = 75:25 to 81:19).…”

“…Subsequent nucleophilic trappingo fg old carbenoid species 18 produces indole 19 bearing an electrondonating substituent at the C3 position.R ecently,w ed isclosed that the gold-catalyzed annulation of azido-diynes 20 with arene 21 leads to the formationo fv arious aryl-annulated [c]carbazoles 22 (Scheme 4). [24] This reaction constructs three bonds and two rings through the initial formation of alkynesubstituted gold carbenoid 18',i ntermolecular arylation with arene 21,a nd 6-endo-dig hydroarylation. [25] Notably,t he reaction using N-Boc-pyrrolea sa rene component 21 afforded pyrrolo[2,3-c]carbazole derivative 23 regioselectively,reflecting the dictyodendrin core structure.…”

Synthesis and Applications of Dihydropyrrolocarbazoles

“…Recently, Ohno and collaborators reported an access to dictyodendrins B, C, E and F using a gold(I)‐catalyzed cascade cyclization of conjugated diynes 149 with pyrroles 150 , leading to the construction of B and C cycles of the dictyodendrin scaffold (Scheme ) , . However, this strategy also afforded the formation of the pyrrolo[3,2‐ c ]carbazole regioisomer in different proportions depending on the substitution of the pyrrole partner 150 .…”