Question

Draw the structure of A, an intermediate in the synthesis of the antipsychotic drug risperidone. Explain why three rings in risperidone are considered aromatic.

Short answer

b. According to Huckel’s rule of aromaticity, a cyclic planar compound is aromatic if it contains (4n+2) pi electrons.

Therefore, in the risperidone molecule, rings A, B, and C are aromatic.

Step-by-step solution

Drug synthesis

Most of the drugs are synthesized from naturally obtained chemicals.

The chemical is modified by a series of chemical reactions which is known as drug synthesis. The synthesis includes oxidation, coupling, and reduction steps.

Some drugs are prepared chemically from smaller easily available starting products.

The starting material for the drugs is found by retrosynthetic analysis of the drug.

Risperidone

Risperidone is an antipsychotic drug used in the treatment of mental disorders or mood disorders.

They are generally used to treat symptoms of schizophrenia and are metabolized in the liver.

The chemical formula for the drug is $C_{23}{H}_{27}F{N}_4{O}_2$ and is sold under the brand name Risperdal.

Synthesis of risperidone

a. In the given reaction, the KOH base abstracts a proton from the compound to form hydroxide anion which undergoes intramolecular reaction removing fluoride ion to form compound A.

b. According to Huckel’s rule of aromaticity, a cyclic planar compound is aromatic if it contains (4n+2) pi electrons.

Therefore, in the risperidone molecule, rings A, B, and C are aromatic.