**6. Recent literature**

Ring-closing metathesis of oxygen-containing dienes with ruthenium catalyst, in H2O as a solvent, provides a good platform for the synthesis of dihydro furan (**Figure 18**) [27].

The hydrosilylation and olefin ring-closing metathesis reaction in the presence of Grubbs-2 catalyst in an aqueous medium is another alternative route (**Figure 19**) [27].

Candida rugosa lipase (CRL) mediated reaction of 1,3-diketone with fumaronitrile resulted in the formation of poly cyano substituted indoles in excellent yields (**Figure 20**) [28].

Polyhydroxyalkyl furans were also prepared from lipase-catalysed Knoevenagel reaction in water using malononitrile and reducing sugars as substrates. Out of the various lipases deployed in the reaction Novozyme-435 showed the highest catalytic activity (**Figure 21**) [28].

**Figure 18.** *Synthesis of dihydrofuran.*

#### **Figure 19.**

*Synthesis of 2,5-dihydrofuran using Grubbs second Generation catalyst.*

#### **Figure 20.**

*Lipase-catalysed synthesis of cyano-containing multisubstituted indoles.*

**Figure 21.** *Lipase-catalysed synthesis of polyhydroxyalkyl furans.*
