Table 1 Synthetic methods of dicoumarols using different types of catalysts

Lewis acids

I₂

I₂ (10 mol%), H₂O, 100 °C, 1 atm, 20–34 h

Ph (97%), 2-HOC₆H₄ (98%)

3-O₂NC₆H₄ (94%), 4-ClC₆H₄ (93%)

4-O₂NC₆H₄ (95%), 4-HOC₆H₄ (98%)

4-MeOC₆H₄ (99%), –CH–CH–C₆H₄ (92%)

Furan-2-yl (93%), thiophen-2-yl (91%)

Indol-3-yl (95%), 3,4-piperonyl (96%)

[45]

MnCl₂

MnCl₂ (10 mol%), H₂O, 100 °C, 20–40 min

MeCH=CH– (95%), Ph (99%)

2-HOC₆H₄ (93%), 4-ClC₆H₄ (99%)

4-HOC₆H₄ (95%), 4-MeOC₆H₄ (97%)

4-O₂NC₆H₄ (99%), furan-2-yl (96%) thiophen-2-yl (95%), indol-2-yl (94%)

[46]

Zn(Proline)₂

Zn(Proline)₂ (5 mol%), H₂O, reflux, 5–9 min

Ph (92%), 2-ClC₆H₄ (96%)

2-HOC₆H₄ (92%), 3-O₂NC₆H₄ (93%)

4-ClC₆H₄ (94%), 4-HOC₆H₄ (96%)

3-MeO-4-HOC₆H₃ (91%)

thiophen-2-yl (93%)

5-Me-thiophen-2-yl (92%)

pyridin-4-yl (91%)

[47]

InCl₃

InCl₃ (10 mol%), H₂O, MW, 110 °C, 15–20 min

Ph (92%), 4-ClC₆H₄ (91%), 4-FC₆H₄ (93%) 4-HOC₆H₄ (90%), 4-MeC₆H₄ (85%)

4-MeOC₆H₄ (87%), 4-O₂NC₆H₄ (96%)

4-HO-3-MeOC₆H₃ (89%)

3,4-(HO)₂C₆H₃ (85%)

4-HO-3,5-(MeO)₂C₆H₂ (86%)

[48]

Lewis and Bronsted acids

Sulfated titania^a (TiO₂/SO₄²⁻)

(TiO₂/SO₄²⁻) (15%), H₂O, 80 ºC, 12–30 min

H (95%), Et (88%), Ph (92%), Pr (90%)

ⁱPr (90%), Me-CH=CH– (92%)

2-HOC₆H₄ (95%), 2-MeOC₆H₄ (85%)

2-O₂NC₆H₄ (90%), 3-BrC₆H₄ (91%)

3-ClC₆H₄ (92%), 3-HOC₆H₄ (84%)

3-MeOC₆H₄ (88%), 3-O₂NC₆H₄ (90%)

4-BrC₆H₄ (94%), 4-ClC₆H₄ (96%)

4-HOC₆H₄ (96%), 4-MeC₆H₄ (89%)

4-MeOC₆H₄ (92%), 4-O₂NC₆H₄ (88%)

4-OH-3-MeOC₆H₃ (89%)

3-OH-4-MeOC₆H₃ (85%)

3,4-(MeO)₂C₆H₃ (90%)

3,4,5-(MeO)₃C₆H₂ (94%)

4-BnO-3-MeOC₆H₂ (82%)

4-CNC₆H₄ (96%), 4-Me₂NC₆H₄ (89%)

Ph-CH=CH– (86%), naphthalen-1-yl (85%)

Furan-2-yl (90%)

[49]

Inorganic acid salts

B(HSO₄)₃

B(HSO₄)₃ (0.3 equiv) (1:1, H₂O–EtOH), 70 °C, 3–6 min

Ph (86%), 3-MeOC₆H₄ (81%)

3-O₂NC₆H₄ (82%), 4-BrC₆H₄ (95%)

4-ClC₆H₄ (92%), 4-NCC₆H₄ (86%)

4-FC₆H₄ (88%), 4-MeC₆H₄ (87%)

4-MeOC₆H₄ (83%), 4-O₂NC₆H₄ (98%)

4-Cl-3-O₂NC₆H₃ (88%)

[50]

Transition metals salts

RuCl₃·nH₂O

RuCl₃·nH₂O (5 mol%), H₂O, 80 °C, 25–35 min

Et (75%), Ph (84%), 4-ClC₆H₄ (85%)

4-NCC₆H₄ (95%), 4-MeOC₆H₄ (92%)

3-(PhO)-C₆H₄ (90%), 2-Cl-6-FC₆H₃ (92%)

3,4-(F₂)C₆H₃ (90%)

2-HO-3-MeOC₆H₃ (84%)

3,4-(MeO)₂C₆H₃ (84%), indol-3-yl (90%)

2-O₂NC₆H₄CH=CH– (90%)

[51]

Ionic liquids

[bmim]BF₄

[bmim]BF₄ (4 equiv)

60–70 °C, 2–3 h

Ph (84%), 3-ClC₆H₄ (84%)

4-BrC₆H₄ (87%), 4-ClC₆H₄ (91%)

4-MeC₆H₄ (83%), 4-MeOC₆H₄ (87%)

4-O₂NC₆H₄ (84%), Me₂CH– (77%)

Ph-CH=CH– (82%), furan-2-yl (83%) pyridin-2-yl (81%)

[52]

SO₃H-functionalized ILs based on benzimidazolium cation

[PSebim][OTf]^b (10 mol%), 70 °C, 2–3 h

Ph (95%), 3-BrC₆H₄ (94%)

3-ClC₆H₄ (94%), 4-BrC₆H₄ (95%)

4-ClC₆H₄ (96%), 4-MeC₆H₄ (93%)

4-MeOC₆H₄ (93%), 4-O₂NC₆H₄ (96%)

4-(H₂C=CH₂)C₆H₄ (92%)

[53]

[MIM(CH₂)₄SO₃H][HSO₄]

[MIM(CH₂)₄SO₃H] [HSO₄] (15 mol%), 80 °C, 18–30 min

Ph (92%), 2-ClC₆H₄ (88%)

2-O₂NC₆H₄ (86%), 3-ClC₆H₄ (89%)

3-O₂NC₆H₄ (89%), 4-ClC₆H₄ (93%)

4-MeC₆H₄ (90%), 4-MeOC₆H₄ (89%)

4-O₂NC₆H₄ (96%)

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Tetramethyl guanidium acetate ([TMG][Ac])

[TMG][Ac] (0.75 mmol), rt, 0.5–4.5 h

Ph (96%), 2-HOC₆H₄ (90%)

2-O₂NC₆H₄ (92%), 3-O₂NC₆H₄ (87%)

4-BrC₆H₄ (96%), 4-ClC₆H₄ (88%)

4-FC₆H₄ (93%), 4-F₃CC₆H₄ (91%)

4-MeC₆H₄ (90%), 4-MeOC₆H₄ (86%)

4-O₂NC₆H₄ (99%), pyridin-4-yl (87%)

3-MeO-4-HOC₆H₃ (84%), furan-2-yl (95%)

(98%)

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Choline hydroxide

ChOH (40%)^c, 50 °C, 1–3 h

H (quantitative), Ph (99%)

2-HOC₆H₄ (99%), 2-O₂NC₆H₄ (75%)

3-O₂NC₆H₄ (93%), 4-BrC₆H₄ (94%)

4-ClC₆H₄ (99%), 4-FC₆H₄ (99%)

4-F₃CC₆H₄ (96%), 4-HOC₆H₄ (94%)

4-MeC₆H₄ (94%), 4-MeOC₆H₄ (95%)

4-HO-3-MeOC₆H₃ (93%), furan-2-yl (98%)

4-O₂NC₆H₄ (89%), pyridin-4-yl (81%) (95%)

[56]

[P₄VPy-BuSO₃H]Cl-X(AlCl₃)^d

IL (0.07 mmol), toluene, 90 °C, 0.5–0.9 h

Ph (95%), 2-HOC₆H₄ (90%)

3-ClC₆H₄ (96%), 3-O₂NC₆H₄ (96%)

4-ClC₆H₄ (93%), 4-MeC₆H₄ (94%)

4-MeOC₆H₄ (92%), 4-HOC₆H₄ (90%)

4-O₂NC₆H₄ (96%), furan-2-yl (91%)

Thiophen-2-yl (91%), pyridin-2-yl (91%) Ph–CH₂–CH₂ (92%), CH₃CH₂CH₂– (92%) Ph-CH=CH– (93%)

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[Dabco-H][AcO]

[Dabco-H][AcO] (10 mol%), H₂O, 80 °C, 2–15 min

n-Pr (99%), Ph (98%), 2-BrC₆H₄ (98%)

3-BrC₆H₄ (98%), 4-BrC₆H₄ (99%)

4-ClC₆H₄ (99%), 4-MeC₆H₄ (96%)

4-MeOC₆H₄ (98%), 4-O₂NC₆H₄ (99%)

2,4-Cl₂C₆H₃ (96%), naphthalen-2-yl (99%) thiophen-2-yl (98%), furan-2-yl (98%)

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Hnmp/ZnCl₃

(Hnmp/ZnCl₃) (20 mg), 100 °C, 30–50 min

Ph (97%), 3-ClC₆H₄ (86%)

3-MeOC₆H₄ (90%), 3-O₂NC₆H₄ (81%)

4-ClC₆H₄ (90%), 4-HOC₆H₄ (81%)

4-MeC₆H₄ (88%), 4-MeOC₆H₄ (93%)

4-O₂NC₆H₄ (86%), 2,4-(MeO)₂C₆H₃ (78%) pyridin-4-yl (90%)

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Heteropoly acids (HPAs)

Phosphotungstic acid

HPA (15 mmol%), H₂O, 80 °C, 14–25 min

Ph (93%), 2-ClC₆H₄ (95%)

2-HOC₆H₄ (98%), 2-O₂NC₆H₄ (96%)

3-O₂NC₆H₄ (94%), 4-ClC₆H₄ (93%)

4-FC₆H₅ (98%), 4-HOC₆H₄ (98%)

4-MeOC₆H₄ (99%), 4-O₂NC₆H₄ (95%)

2,4-Cl₂C₆H₃ (92%), 2,6-Cl₂C₆H₃ (98%)

–CH=CH–C₆H₄ (98%), 3,4-piperonyl (96%)

Indol-3-yl (95%), thiophen-2-yl (91%)

Furan-2-yl (93%), 4-F₃CC₆H₄ (98%)

4-Me₂C₆H₃ (90%), 3,4-(MeO)₂C₆H₃ (90%)

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Phase transfer catalysts and surfactants

Tetrabutyl ammonium bromide (TBAB)^e,f

TBAB (10 mol%), H₂O, 100 °C

Ph (92%), 3-ClC₆H₄ (87%)

4-BrC₆H₄ (88%), 4-ClC₆H₄ (95%)

4-MeC₆H₄ (92%), 4-MeOC₆H₄ (84%)

4-O₂NC₆H₄ (91%), Ph–CH=CH– (82%)

3,4-(MeO)₂C₆H₃ (87%), Me₂CH– (82%)

3,4,5-(MeO)₃C₆H₂ (84%), piperonyl (88%) furan-2-yl (88%), pyridin-2-yl (90%)

4-(Me)₂CHC₆H₄ (91%)

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Sodium dodecyl sulfate (SDS)

SDS (20 mol%), H₂O, 60 °C, 2.30–3.0 h

Ph (90%), 2-MeC₆H₄ (84%)

3-ClC₆H₄ (92%), 3-O₂NC₆H₄ (95%)

4-BrC₆H₄ (91%), 4-ClC₆H₄ (93%)

4-FC₆H₄ (94%), 4-MeC₆H₄ (97%)

4-(Me)₂NC₆H₄ (94%), 4-MeOC₆H₄ (97%) 4-O₂NC₆H₄ (98%), 3,4-(MeO)₂C₆H₃ (98%)

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Modified glycerols

Propane-1,2,3-triyl tris(hydrogen sulfate) (PTTH)

PTTH (0.03 mol%), 80 °C, H₂O, 7–10 min^g or solvent-free, 5–8 min

H (80%), Ph (90%), 2-ClC₆H₄ (85%)

3-O₂NC₆H₄ (95%), 4-ClC₆H₄ (90%)

4-HOC₆H₄ (85%), 4-MeC₆H₄ (90%)

4-MeOC₆H₄ (85%), 4-O₂NC₆H₄ (95%)

3,4-(MeO)₂C₆H₃ (85%), Ph-CH=CH– (85%) furan-2-yl (80%)

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