Domain: Medicinal organic chemistry

A fluoroquinolone drug (D) is synthesized using the following steps:

Step-1: 2,3,4-Trifluoroaniline reacts with diethyl ethoxymethylenemalonate to form compound (A).

Step-2: Compound (A) is reacted with ethyl iodide in the presence of potassium carbonate (K_2CO_3) and N,N-dimethylformamide (DMF) as the polar protic solvent to produce intermediate (B).

Step-3: Intermediate (B) undergoes hydrolysis in dilute hydrochloric acid (HCl) to yield compound (C).

Step-4: Compound (C) undergoes a regioselective nucleophilic aromatic substitution with 2-methylpiperazine in the presence of pyridine as a base to produce the final fluoroquinolone drug (D).

Predict the molecular formula of (D).

Grading rubric:
criterion: Correctly characterizes the initial condensation and thermal cyclization as a Gould-Jacobs reaction sequence generating the bicyclic 4-oxoquinoline core.
weight: 10
criterion: Correctly validates the conservation of the 6,7,8-trifluoro substitution pattern in the quinolone intermediate A.
weight: 10
criterion: Correctly deduces the regioselectivity of the alkylation step, confirming the attachment of the ethyl group to the quinolone nitrogen (N-1) under basic conditions.
weight: 10
criterion: Correctly identifies the transformation of the C-3 ester functionality to the free carboxylic acid via acid-catalyzed hydrolysis.
weight: 10
criterion: Correctly identifies the C-7 carbon as the specific electrophilic site for nucleophilic aromatic substitution (SN_Ar), justified by the vinylogous activation from the C-4 carbonyl.
weight: 20
criterion: Correctly determines the regiochemistry of the nucleophilic attack by 2-methylpiperazine, specifying bond formation via the sterically unhindered distal nitrogen (N-4).
weight: 20
criterion: Correctly verifies the stoichiometry of the substitution, confirming the displacement of exactly one fluoride atom while retaining the C-6 and C-8 fluorines.
weight: 10
criterion: Correctly derives the final molecular formula C_17H_19F_2N_3O_3 by integrating the backbone modification, substituent addition, and leaving group loss.
weight: 10

Answer:
C17H19F2N3O3