Isoquinoline

Isoquinoline is an aromatic heterocyclic compound with a benzene ring fused to a pyridine ring. Its molecular formula is C₉H₇N.

Pyridine: Pyridine is an aromatic six-membered ring containing one nitrogen atom. Isoquinoline’s nitrogen-containing ring has pyridine-like structure.
Quinoline: Quinoline is an aromatic bicyclic heterocycle composed of fused benzene and pyridine rings. It is isoquinoline’s constitutional isomer, with nitrogen in a different ring position.
Pyridine basicity: Pyridine basicity arises from protonation at nitrogen’s in-plane lone pair. Isoquinoline’s nitrogen lone pair likewise accepts a proton without disrupting aromaticity.
Isoquinoline alkaloids: Isoquinoline alkaloids are natural products whose structures contain an isoquinoline-derived nitrogen framework. Many natural products build on the fused nitrogen-containing scaffold.
Alfred Pictet: Alfred Pictet was a Swiss chemist known for research on alkaloids and heterocyclic compounds. His work included early synthesis of isoquinoline.
Benzene: Benzene is a six-carbon aromatic ring with formula C₆H₆. A benzene ring is fused to isoquinoline’s pyridine ring.
Indole: Indole is a bicyclic aromatic heterocycle with a benzene ring fused to a pyrrole ring. Its fused nitrogen ring is five-membered, unlike isoquinoline’s six-membered ring.
Electrophilic aromatic substitution: Electrophilic aromatic substitution replaces a ring hydrogen with an electrophile while retaining aromaticity. Isoquinoline’s electron-poor nitrogen influences where electrophilic substitution occurs.
Papaverine: Papaverine is a benzylisoquinoline alkaloid used as a smooth-muscle relaxant and vasodilator. Its structure contains an isoquinoline-derived framework.
Pomeranz–Fritsch reaction: The Pomeranz–Fritsch reaction synthesizes isoquinolines from benzaldehydes and aminoacetaldehyde acetals under acidic conditions. It is a named route for constructing the isoquinoline ring system.

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