Synthesis of Benzofulvenes through Rhodium-Catalyzed Transannulation of Enynyl Triazoles

Abstract

Rhodium-catalyzed denitrogenative cyclization of (E)-ethyl 2-(1-alkyl and arylsulfonyl-1H-1,2,3-triazol-4-yl)-3-aryl acrylate generated from (E)-ethyl 2-benzylidenebut-3-ynoates and N-sulfonyl azides in the presence of a copper catalyst was developed for the synthesis of a large number of functionalized benzofulvenes. Moreover, the synthesis of benzofulvenes was demonstrated as a one-pot method through tandem copper-catalyzed [3 + 2] cycloaddition and rhodium-catalyzed denitrogenative cyclization from (E)-ethyl 2-benzylidenebut-3-ynoates and N-sulfonyl azides.

Copper(I)‐catalyzed Cyclization Reactions of Ethyl (E)‐α‐Ethynyl‐β‐Aryl‐α,β‐Unsaturated Esters with N‐Sulfonyl Azides: Synthesis of 1‐Aminonaphthalene, 3‐Aminobenzofuran, and 3‐Aminothiobenzofuran Derivatives

“…In addition, the synthesis of benzofulvenes was proved as a one‐pot method through tandem Cu(I)‐catalyzed [3 + 2] cycloaddition followed by Rh(II)‐catalyzed denitrogenative cyclization from ethyl ( E )‐α‐ethynyl‐β‐aryl‐α,β‐unsaturated esters and N ‐sulfonyl azides (Eq. 2) . Moreover, a Cu(I)‐catalyzed 1,3‐dipolar cycloaddition followed by ring‐chain isomerization to ketenimine formation tandem process was reported by Chang et al .…”

“…Recently, we developed Rh‐catalyzed denitrogenative cyclization of ( E )‐ethyl 2‐(1‐alkyl and arylsulfonyl‐1 H ‐1,2,3‐triazol‐4‐yl)‐3‐arylacrylate obtained from ethyl ( E )‐α‐ethynyl‐β‐aryl‐α,β‐unsaturated esters and N ‐sulfonyl azides with a copper(I) catalyst for the synthesis of a variety of functionalized benzofulvenes (Scheme , Eq. 1) . In addition, the synthesis of benzofulvenes was proved as a one‐pot method through tandem Cu(I)‐catalyzed [3 + 2] cycloaddition followed by Rh(II)‐catalyzed denitrogenative cyclization from ethyl ( E )‐α‐ethynyl‐β‐aryl‐α,β‐unsaturated esters and N ‐sulfonyl azides (Eq.…”

Indium-Catalyzed Denitrogenative Transannulation of Pyridotriazoles: Synthesis of Pyrido[1,2-a]indoles

“…Based on the literature reports ,,− and with the above observations, a plausible reaction mechanism has been proposed (Scheme ). Denitrogenation of 1 with indiumtriflate (In­(OTf) 3 ) may generate the indium carbenoid A .…”

“…Based on the recent literature − for the generation of metal carbene intermediates through the ring opening of pyridotriazole 1a (Scheme ), we hypothesized to employ silver and indium as metal catalysts to generate electrophilic carbene intermediate A , and its subsequent reaction with 2-naphthol 2a as nucleophile to generate tetracyclic heterocycle 3a′ (5-phenylnaphtho­[2,1- b ]­pyrido­[1,2- d ]­[1,4]­oxazine) in line with our interest in the synthesis of fused heterocycles and transannulation of pyridotriazoles . Instead, we obtained an interesting product 3a 1-(pyrido­[1,2- a ]­indol-10-yl)­naphthalen-2-ol in 20% isolated yield, when Ag­(OTf) was used as catalyst (20 mol %) in dichlorobenzene (DCB) as solvent at 120 °C, after 5 h (Table , entry 1).…”

A Simple and Mild Microwave-Based Synthesis of Novel Functionalized Benzofulvenes

“…Furthermore, many preparations use metal catalysts that must be fully removed before any applied use of the fulvene. 6 Recently, there has been an effort to focus on cyclization reactions of enediynes, 7 alkynyl derivatives, 8 and transition-metal-based transformations 9 to obtain these valuable functionalized fulvenes. While these methods have greatly improved our abilities to access a wealth of benzofulvene-based motifs, there is arguably room in this mix for a simple and effective synthetic solution.…”