Electroreductive Intermolecular Coupling of Coumarins with Benzophenones: Synthesis of 4-(2-Hydroxyphenyl)-5,5-diaryl-γ-butyrolactones, 2-(2,2-Diaryl-2,3-dihydrobenzofuran-3-yl)acetic Acids, and 4-(Diarylmethyl)coumarins

Abstract

The electroreductive coupling of coumarins with benzophenones in the presence of TMSCl gave adducts reacted at the 4-position of coumarins as trimethylsilyl ethers. From 3-methylcoumarin, 3,4-cis-adducts were formed stereoselectively. The de-trimethylsilylation of the adducts with 1 M HCl aq or TBAF in THF at 25 °C produced 4-(2-hydroxyphenyl)-5,5-diaryl-γ-butyrolactones. The γ-butyrolactones were further transformed to 2-(2,2-diaryl-2,3-dihydrobenzofuran-3-yl)acetic acids by treatment with 1 M HCl aq at reflux temperature. The de-trimethylsilylation of the adducts with 1 M HCl in MeOH afforded 2-(2,2-diaryl-2,3-dihydrobenzofuran-3-yl)acetic acid methyl esters. The de-trimethylsiloxylation of the adducts or dehydration of the γ-butyrolactones brought about 4-(diarylmethyl)coumarins.

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

“…according to our already reported method [3][4][5][6] and the results are summarized in Table 1. was carried out in THF containing TMSCl (5 equiv.)…”

“…according to our already reported method [3][4][5][6] and the results are summarized in Table 1. We have already observed similar cis-stereoselectivity in the electroreductive coupling of 1-alkoxycarbonyl-3-methoxycarbonylindoles, [4] 5-substituted 1,3-dimethyluracils, [5] and 3-methylcoumarin [6] with aromatic ketones. It is noted that the electroreductive coupling of 3-methylchromone (1b) and isoflavone (1c) with 2a,b,d gave the adducts 3g-k as single diastereomers (>99 % selectivity by 1 H NMR analysis) (runs [7][8][9][10][11].…”

“…Since we already reported CV data of benzophenones 2a-g, [6] we measured the CV of chromones 1a-g under the same conditions to compare their first reduction peaks (Table 3). silyl)chroman-2-one (ii) were formed in 35 % (60:40 dr) and 8 % yields, respectively.…”

“…1 H NMR (500 MHz, CDCl 3 ): δ = 3.81 (s, 3H), 6.14 (d, 1H, J = 2.2 Hz), 6.52 (dd, 1H, J = 8.6, 2.2 Hz), 6.55 (s, 1H), 6.97-7.02 (m, 2H), 7.08-7.13 (m, 3H), 7.20-7.40 (m, 9H), 7.54-7.58 (m, 2H). R f : 0.5 (hexanes/ethyl acetate, 5:1).…”

“…marins [6] with carbonyl compounds. In this regard, we attempted the electroreductive cross-coupling of chromones with carbonyl compounds, since this reaction is expected to provide a new synthetic route to 2-subsutituted chromones.…”