**7.5 Synthesis of π-conjugated polycyclic** *N***-Heteroaromatic molecules** *via* **C-H/N-H oxidative alkyne annulation**


**Figure 30.** *Ru(II)-catalyzed synthesis of Isoquinoline derivatives.*

**Figure 31.** *Ruthenium(II)-catalyzed synthesis of Indolo[2,1-*a*]isoquinolines and Pyrrolo[2,1-*a*]isoquinolines.*

*Access to* N*-Heterocyclic Molecules* via *Ru(II)-Catalyzed Oxidative Alkyne… DOI: http://dx.doi.org/10.5772/intechopen.95987*

**Figure 32.** *Cationic ruthenium(II)-catalyzed synthesis of Pyrazolo[5,1-*a*]isoquinolines.*

**Figure 33.** *Ruthenium(II)-catalyzed synthesis of Imidazo[2,1-*a*]isoquinolines.*

#### **Figure 34.**

*Ruthenium(II)-catalyzed synthesis of tetracyclic Heteroarenes.*


functionalization involves Ru-N covalent bond while the second C-H functionalization most likely involves Ru-O coordinate bond.

vii. In 2018 Gogoi et al. reported an unprecedented Ru(II)-catalyzed N-H/C-H activation and annulation reaction of of *N*-arylpyrazol-5-ones and diaryl/arylalkyl-substituted alkynes in the presence of bidented ligand 1,3-bis(diphenylphosphino)propane for the synthesis of quinazolines

**Figure 35.**

*Ruthenium(II)-catalyzed external oxidant FreeSynthesis of tetracyclic Heteroarenes.*

#### **Figure 36.**

*Ruthenium catalyzed synthesis of Benzopyran-fused 2-pyridones.*

**Figure 37.** *Ruthenium(II)-catalyzed synthesis of Quinozaline.*

*Access to* N*-Heterocyclic Molecules* via *Ru(II)-Catalyzed Oxidative Alkyne… DOI: http://dx.doi.org/10.5772/intechopen.95987*

> (**Figure 37**) [56]. This annulation reaction proceeds mainly via oxidation of Ru(II) to Ru(IV) by cleavage of the N-N bond and cleavage of the triple bond of the alkyne.

**Figure 38.** *Ruthenium(II)-catalyzed synthesis of polycyclic Isoquinolinones.*

**Figure 39.** *Ruthenium(II)-catalyzed synthesis of conjugated fused Isoquinolines.*

	- ix. In 2019 Patel *et al.* developed a one-pot sequential synthesis of highly conjugated fused isoquinolines via Cu(II)-catalyzed intramolecular cyclization followed by Ru(II)-catalyzed C-H/N-H oxidative alkyne annulation reactions (**Figure 39**) [58]. This one pot synthesis consisting of selective hydrolysis of a cyano group to an amide, dehydrative cyclization of the amide to a cyclic amide, aromatization of the cyclic amide (2-oxo-1,2,3,4-tetrahydropyridine moiety) to a 2-oxo-1,2-dihydropyridine and finally, the C-H/N-H annulation with an internal alkyne.
