Electroreductive Intermolecular Coupling of Chromones with Benzophenones: Synthesis of 2‐Diarylmethylchromones and Tetrasubstituted Furans

Abstract

The electroreductive coupling of chromones with benzophenones in the presence of TMSCl gave adducts reacted at the 2‐position of chromones as trimethylsilyl ethers. From 3‐methyl‐ and 3‐phenylchromones, 2,3‐cis‐adducts were formed predominantly. The cis‐adducts were isomerized to trans‐ones by treatment with DBU. The detrimethylsilylation of the adducts with 1 M HCl aq/dioxane produced the corresponding alcohols. The dehydrosiloxylation of the adducts or dehydration of the desilylated alcohols brought about 2‐diarylmethylchromones. The detrimethylsilylation of the adducts with TBAF and subsequent treatment with NaH afforded ring‐opening products. The dehydration of the ring‐opening products obtained from 3‐methyl‐ and 3‐phenylchromons brought about tetrasubstituted furans or dihydrobenzofuran‐3‐ones. The dehydrogenation of the adducts with DDQ and subsequent desilylation with 1 M HCl aq/dioxane gave 2‐(diarylhydroxymethyl)chromones.

Electroreductive Intermolecular Coupling of 4-Quinolones with Benzophenones: Synthesis of 2-Substituted 4-Quinolones

“…These results show that 2 are generally more reducible than 1 , although the differences of E p values between 1-alkoxycarbonyl-4-quinolones 1b – k , 1m , 1n and 2a – e are relatively small. From these results of CV data and our previously reported results of the reductive coupling of other heterocycles with 2 , 5−8 the reaction mechanism of the electroreductive coupling of 1 (except for 1i – k ) with 2 can be presumed as illustrated in Scheme 9. Initially, carbanion A is generated by the two-electron transfer to 2 and O-silylation with TMSCl.…”

“…The stereostructure of 3k was confirmed to be cis by X-ray crystallographic analysis, and this complete cis-selective formation of 3k was in accordance with our previously reported results for the electroreductive coupling of other heterocycles with 2a . 5−8 The desilylation of cis - 3k with TBAF produced cyclic carbamate 5g as a diastereomeric mixture (cis/trans = 25:75) due to the isomerization of cis - 5g to trans - 5g .…”

“…First, the electroreduction of 1-methyl-4-quinolone ( 1a ) with benzophenone ( 2a ) (2 equiv) in tetrahydrofuran (THF) containing TMSCl (5 equiv) was carried out (2 F/mol for 2a ) according to our already reported method − (Scheme ). The product coupled at the 2-position of 1a with 2a was obtained as a trimethylsilyl ether 3a in 31% yield and more than 50% of unreacted 1a was recovered.…”

“… Therefore, the synthesis of 4-quinolone derivatives has extensively been studied . On the other hand, we have reported the electroreductive cross-coupling of heterocycles, such as phthalimides, indoles, uracils, coumarins, and chromones with carbonyl compounds. In this context, we attempted the electroreductive cross-coupling of 4-quinolones with carbonyl compounds since this reaction is expected to provide a new synthetic route to 2-subsutituted 4-quinolones .…”

Synthesis of Tetrasubstituted Furans through One-Pot Formal [3 + 2] Cycloaddition Utilizing [1,2]-Phospha-Brook Rearrangement

“…Thus, in recent years, the construction of tetrasubstituted furan rings through the cycloaddition of multiple components has been intensively studied. 7,8 Although various types of reactions have been developed, methods that provide efficient access to a wide range of tetrasubstituted furans from readily available starting compounds are still limited.…”