**2.9 Other methods**

CuOAc-catalyzed hydroarylation of methyl phenylpropiolates **124** having a methoxy methyl (MOM)-protected hydroxyl group at the ortho-position with various arylboronic acids followed by acidic workup leads to 4-arylcoumarins **59** in good to excellent yields (**Figure 37**) [128].

Substituted coumarins **126** are obtained in moderate to excellent yields by Yb(OTf)3-catalyzed reactions of substituted phenols **1** with alkylidene Meldrum's acid **125** in CH3NO2 at 100°C (**Figure 38**) [129].

A series of 3-alkylcoumarins **128** are obtained in moderate yields from 2-hydroxybenzaldehydes **18** and α,β-unsaturated aldehydes **127** via generation of *N*-heterocyclic carbenes (NHC) in ionic liquid under conventional heating (**Figure 39**, Condition A) and/or microwave irradiation conditions (**Figure 39**, Condition B) [130].

3-Benzoylcoumarins **130/131** and coumarin-3-carbaldehydes **47** have also been isolated in moderate to good yields from the reactions of 2-hydroxybenzaldehydes **18/19** with phenylpropionyl chloride **129a** and/or propionyl chloride **129b** under esterification conditions (**Figure 40**) [131].

An electrochemical method has been developed for the synthesis of 6*H*-benzo[*c*] chromen-6-ones **133** in good to excellent yields from biphenyl-2-carboxylic acids **132** via radical arene carbon–oxygen bond formation reaction (**Figure 41**) [132].

**Figure 38.** *Synthesis of substituted coumarins.*

**127**

*One-Pot Synthesis of Coumarin Derivatives DOI: http://dx.doi.org/10.5772/intechopen.89013*

The method involves DDQ as a redox mediator, inexpensive glassy carbon electrodes to facilitate an intramolecular lactonization of biphenyl-2-carboxylic acid

In this chapter, we have discussed a plethora of methods for the one-pot synthesis of coumarin derivatives and their advantages and/or demerits compared to other methods. Both the Pechmann as well as Knoevenagel condensation reactions under microwave and/or ultrasound irradiation conditions, and catalyzed by ionic liquids and/or solid acids have several advantages including high products yields, diminutive reaction times, ease of isolation of products, recycle of catalysts, and green aspects by avoiding toxic catalysts and solvents. Chemo- and regioselective syntheses of 3-substituted coumarins have been reported via Baylis-Hillman reactions under mild conditions. On the other hand, vinyl phosphonium salt-mediated electrophilic substitution reactions of phenols afford 4-carboxyalkyl coumarin derivatives in good yields under neutral conditions. This method offers significant advantages for the synthesis of coumarins having acid sensitive functional groups. In contrast, the most widely used method von Pechmann condensation requires acidic conditions. Moreover, palladium-catalyzed Heck lactonization protocol has been employed for the regioselective synthesis of coumarin derivatives from *o*-iodophenols and enoates. It is revealed that this reaction is sensitive to steric hindrance around the double bound in the enoates. Regioselective synthesis of 3,4-disubstituted coumarins

Bu4NClO4 electrolyte mixture

derivatives, and 2,6-lutidine as an additive, in 0.1 M <sup>n</sup>

*Synthesis of 3-benzoyl coumarins and coumarin-3-carbaldehyde.*

of 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP).

**3. Concluding remarks**

*Synthesis of 6*H*-benzo[*c*]chromen-6-ones.*

**Figure 40.**

**Figure 41.**

**Figure 39.** *Synthesis of 3-alkylcoumarins.*

*One-Pot Synthesis of Coumarin Derivatives DOI: http://dx.doi.org/10.5772/intechopen.89013*

**Figure 40.**

*Phytochemicals in Human Health*

(**Figure 35**) [126].

**2.9 Other methods**

Condition B) [130].

good to excellent yields (**Figure 37**) [128].

acid **125** in CH3NO2 at 100°C (**Figure 38**) [129].

esterification conditions (**Figure 40**) [131].

dicarbonylation process in the presence of KI in MeOH at room temperature

sequential reactions for the synthesis of substituted coumarins.

Furthermore, electrophilic palladium-catalyzed cycloisomerization of brominated arylpropiolates **122** followed by Suzuki coupling with arylboronic acids furnishes 4-arylcoumarins **123** in moderate to good yields (**Figure 36**) [127]. This strongly suggests that a single loading of catalyst Pd(OAc)2 could be used to conduct

CuOAc-catalyzed hydroarylation of methyl phenylpropiolates **124** having a methoxy methyl (MOM)-protected hydroxyl group at the ortho-position with various arylboronic acids followed by acidic workup leads to 4-arylcoumarins **59** in

Substituted coumarins **126** are obtained in moderate to excellent yields by Yb(OTf)3-catalyzed reactions of substituted phenols **1** with alkylidene Meldrum's

3-Benzoylcoumarins **130/131** and coumarin-3-carbaldehydes **47** have also been isolated in moderate to good yields from the reactions of 2-hydroxybenzaldehydes **18/19** with phenylpropionyl chloride **129a** and/or propionyl chloride **129b** under

An electrochemical method has been developed for the synthesis of 6*H*-benzo[*c*] chromen-6-ones **133** in good to excellent yields from biphenyl-2-carboxylic acids **132** via radical arene carbon–oxygen bond formation reaction (**Figure 41**) [132].

A series of 3-alkylcoumarins **128** are obtained in moderate yields from 2-hydroxybenzaldehydes **18** and α,β-unsaturated aldehydes **127** via generation of *N*-heterocyclic carbenes (NHC) in ionic liquid under conventional heating (**Figure 39**, Condition A) and/or microwave irradiation conditions (**Figure 39**,

**126**

**Figure 39.**

*Synthesis of 3-alkylcoumarins.*

**Figure 38.**

*Synthesis of substituted coumarins.*

*Synthesis of 3-benzoyl coumarins and coumarin-3-carbaldehyde.*

**Figure 41.** *Synthesis of 6*H*-benzo[*c*]chromen-6-ones.*

The method involves DDQ as a redox mediator, inexpensive glassy carbon electrodes to facilitate an intramolecular lactonization of biphenyl-2-carboxylic acid derivatives, and 2,6-lutidine as an additive, in 0.1 M <sup>n</sup> Bu4NClO4 electrolyte mixture of 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP).
