DABCO‐Catalysed [3+2] Cyclization/Deformylation Cascade of p‐Quinols with 3‐Formylchromones: Access to Benzopyrone‐Fused Tetracyclic Ring Systems

Abstract

The construction of benzopyrone‐fused hydrobenzofuranones via DABCO‐catalyzed [3+2] cyclization/deformylation cascade of p‐quinols with 3‐formylchromones is described. The reaction works under mild reaction conditions to provide the desired products in 53–90% yields with complete diastereoselectivities. In addition, an enantioselective version with 81% ee is also realized in the presence of Takemoto's chiral thiourea catalyst.

Strategies and Methods for the Catalytic Asymmetric Synthesis of Benzofuran/Benzopyran Fused Acetals: A Review

“…[39] Later in 2021, the Jørgensen group reported an asymmetric O-hetero-Diels-Alder reaction using 3substituent-4H-chromen-4-one 37 and 4-hydroxy-2enal 38 as substrates, affording products 39 in excellent yields and ees (Scheme 20, up to 85% yield, 99% ee and > 20:1 dr) [40] Very recently, Liu, Chen and coworkers developed a chiral cinchona alkaloid catalyzed tandem to afford product 42 in moderate yield with 81% ee (Scheme 21). [41] At the same year, a hydrogen-bonding catalystcontrolled enantioselective construction of a complex polycyclic system bearing five stereocenters in an operationally simple procedure was revealed by Lin group. [42] The matched hydrogen-bond interactions between the cinchona-alkaloid derived catalyst Cat.6 and the substrates were beneficial for the excellent diastereo-and enantiocontrol in the cascade reaction (Scheme 22).…”

Synthesis of 6/5/3-Fused Tricyclic Scaffolds via Multistep Cascade Cyclization of α-Aryl Vinylsulfoniums with para-Quinamines and para-Quinols

“…The para -quinamines and para -quinols, as significant subclasses of cyclohexadienones, are distinguished by their NH and OH nucleophilic site, which can act as N­(O)–C–C synthons to participate in formal [3 + n ] cyclization reactions with various reactive partners, thereby leading to the formation of fused nitrogen- and oxygen-containing heterocycles (Scheme , top) . Among these, the [3 + 2] cycloaddition reactions with C–C synthons show unparalleled advantages in constructing the hydroindoline-5-one and hydrobenzofuran-5-one skeletons. , Additionally, the presence of multiple active sites in para -quinamines and para -quinols enables the possibility of multistep cascade reactions, which further enhances their utility in the one-pot synthesis of fused polycyclic products. However, organic synthetic chemists have paid limited attention to the multistep cascade reactions of para -quinamines and para -quinols, and only a few reports are currently available (Scheme , top) .…”