Formal [3+2] Annulation of Copper‐Allenylidenes with 3‐Oxo‐3‐Arylpropanenitriles: Synthesis of Tetrasubstituted Furans

Abstract

The copper-catalyzed decarboxylative [3 + 2] annulation of ethynyl benzoxazinanones with 3-oxo-3-arylpropanenitriles has been developed, producing tetrasubstituted furan derivatives in moderate to high yield. This reaction was generally compatible with a wide range of substrates. Notably, the intermediate copper-allenylidenes worked as a C2 synthon in the cycloaddition reaction.

Base‐Mediated Decarboxylative [3+2] Annulation of Ethynyl Benzoxazinanones and Benzimidamides: Synthesis of Imidazole Derivatives

“…When transition metal catalyst such as copper catalyst was used, the propargylic compounds generate metal‐allenylidene intermediates through decarboxylation, which then work as an electrophile to furnish diverse annulation reactions [1,2] . Generally, in the presence of a copper catalyst, ethynyl benzoxazinanones produced the copper‐allenylidene intermediates, which act as a four, three or two‐membered synthon to accomplish intermolecular [4+n], [3+n] and [2+n] annulations (Scheme 1a) [3–13] . The versatility of copper‐allenylidene as four‐membered synthon had been demonstrated by [4+1] annulation of ethynyl benzoxazinanones with sulfur ylides, [3] several asymmetric [4+2] annulation reactions of ethynyl benzoxazinanones with different bisnucleophiles, [4–10] and asymmetric [4+3] cycloaddition of ethynyl benzoxazinanones with C,N‐cyclic azomethine imines [11] .…”

“…Only example about the use of copper‐allenylidenes as three‐membered synthon was asymmetric [3+3] annulation of pyrazolones with ethynyl benzoxazinanones [12] . Most recently, we revealed the use of copper‐allenylidenes as two‐membered synthon in a [3+2] annulation of ethynyl benzoxazinanones with 3‐oxo‐3‐arylpropanenitriles [13] . Besides intermolecular annualtion reactions, copper‐allenylidene was also a useful intermediate for intramolecular annulation (Scheme 1a) [14–16] .…”

Recent advances in copper-catalyzed decarboxylative reactions of propargylic cyclic carbonates/carbamates

“…18). 34 This method presented broad substrate scope, allowing the formation of various tetrasubstituted furan derivatives 43 in moderate to high yields (36–99%). However, when ethynyl benzoxazinanones 1 bearing substituents at the 5- and 8-positions of the benzene ring were used as substrates, the reactions failed to give the desired products, which may be attributed to the steric hindrance.…”

Advancements in Asymmetric Catalytic Approaches Involving Benzoxazinone Derivatives

“…Afterwards, the moiety of the alkynyl group acting as a C2 synthon in the racemic annulation reaction was reported respectively. [61]…”