Tunable Synthesis of Indeno[1,2-c]furans and 3-Benzoylindenones via FeCl₃-Catalyzed Carbene/Alkyne Metathesis Reaction of o-Alkynylbenzoyl Diazoacetates

Abstract

An efficient synthesis of indeno­[1,2-c]­furan and 3-benzoylindenone derivatives through a FeCl3-catalyzed carbene/alkyne metathesis reaction of o-alkynylbenzoyl diazoacetates is presented. Mechanistically, the key intermediate, vinyl iron carbene, is formed by 5-exo-dig carbocyclization and terminated with a formal [3 + 2] cycloaddition or carbonylation. To the best of our knowledge, this is the first example in which FeCl3 is used as a catalyst for a carbene/alkyne metathesis reaction. Finally, derivatization reactions were carried out to showcase the value of the products.

Synthesis of Indeno[1,2-c]furans via Cobalt-Catalyzed Radical–Polar Crossover [3 + 2] Cycloaddition of o-Alkynylaryl β-Dicarbonyls

“…16−21 For instance, Fan and co-workers have developed a FeCl 3 -catalyzed carbene/alkyne metathesis reaction of o-alkynylbenzoyl diazoacetates for the preparation of indeno[1,2-c]furans, in which a putative vinyl iron carbene intermediate was involved (Scheme 1A). 22 A similar transformation has been realized also by Hashmi and co-workers, wherein α,α-diketo gold carbenoid 23−25 was generated through oxygen transfer from an N-oxide onto the gold-activated alkynone (Scheme 1B). 26 Herein, we report a mechanistically distinct, radical−polar crossover strategy 27,28 for the generation of indeno[1,2c]furans (Scheme 1C).…”

“…Among various fused polycyclic furans, indeno­[1,2- c ]­furan is an interesting polycyclic scaffold, featuring a fused furan and indenone framework. − Retrosynthetically, the most common approach to access indeno­[1,2- c ]­furans is the oxidative 2-fold cyclization of o -alkynylaryl tethered metal carbenoids. − For instance, Fan and co-workers have developed a FeCl 3 -catalyzed carbene/alkyne metathesis reaction of o -alkynylbenzoyl diazoacetates for the preparation of indeno­[1,2- c ]­furans, in which a putative vinyl iron carbene intermediate was involved (Scheme A) . A similar transformation has been realized also by Hashmi and co-workers, wherein α,α-diketo gold carbenoid − was generated through oxygen transfer from an N -oxide onto the gold-activated alkynone (Scheme B) …”

Recursive Anion-Triggered Tandem Reactions of ortho-Bis-ynones: Tunable Synthesis of 1-Indenones and Cyclopenta[a]inden-8(2H)-ones

“…Given these diverse utilitarian attributes, it is natural that syntheses of 1-indenones continue to receive widespread attention and employ a variety of synthetic tactics. 14,15 These approaches, though effective in many contexts, are also self-limiting in some others, particularly for accessing unsymmetrical 2,3-disubstituted 1-indenones that are presently in demand for diverse applications. Thus, the formation of 2,3-disubstituted 1-indenone 11a in our pilot study (vide supra) provided the impetus to scope this promising synthetic lead.…”

Cationic Gold‐Catalyzed Intramolecular Cyclization of Substituted 1,5‐Diynes to Access Indenone Derivatives

“…[18] Fan and co-workers reported synthesis of indenones from o-alkynyl benzoyl diazoacetates under iron catalysis [Scheme 1 (ii)]. [19] Indenones were achieved from 1,2-dialkynylbenzenes in the presence of palladium and cooper catalytic system [Scheme 1 (iii)]. [16b] Reaction of 1,2-dialkynylbenzenes with sulfur produced the corresponding indenones [Scheme 1 (iv)].…”

“…Visible light promoted reaction was developed by Reizer et al ., to access the indenone derivatives from o ‐alkylated ‐ α ‐bromocinnamates [Scheme 1 (i)] [18] . Fan and co‐workers reported synthesis of indenones from o ‐alkynyl benzoyl diazoacetates under iron catalysis [Scheme 1 (ii)] [19] . Indenones were achieved from 1,2‐dialkynylbenzenes in the presence of palladium and cooper catalytic system [Scheme 1 (iii)] [16b] .…”