Domain: Organic synthesis

Predict the molecular weight of the major product (compound $\text{C}$) obtained from a three-step sequence.Step-$1$: $\text{Methyl propiolate}$ ($16.86$ mmol) was added to a solution of $\text{3-methyl-1-(methylamino)indole}$ ($4.69$ mmol) in $\text{methanol}$ ($20$ mL) at room temperature, the mixture was refluxed for $14$ $\text{h}$, affording compound $\text{A}$.Step-$2$: Compound $\text{A}$ ($2.56$ mmol) was heated in $\text{diphenyl ether}$ ($8$ mL) at $210–220$ $^\circ\text{C}$ for $2$ $\text{h}$ $50$ min to furnish compound $\text{B}$.Step-$3$: Compound $\text{B}$ ($0.98$ mmol) in anhydrous $\text{dichloromethane}\ (\text{CH}_2\text{Cl}_2$) ($15$ mL) containing $15$-crown-$5$ ($2$ $\text{mg}$) and $\text{sodium\ hydride}$ $\text{(NaH)}$ ($80$%; $3$ mmol) was treated with excess $\text{methyl iodide}$ ($5$ mmol) and refluxed for $15$ h to give compound $\text{C}$.

Grading rubric:
criterion: Does the response correctly identify the application of Aza-Michael Addition mechanism (MeOH, rt, 14h) in step 1?
weight: 10
criterion: Correct identification of compound A as methyl (E)-3-(methyl(3-methyl-1H-indol-1-yl)amino)acrylate from Step-1.
weight: 10
criterion: Does the response correctly identify the application of 3,3-Sigmatropic Rearrangement mechanism (PhOPh, 210-220\( °C\), 50 min.) in step 2?
weight: 10
criterion: Correct identification of compound B as methyl (3aR,8aS)-1,3a-dimethyl-1,3a,8,8a-tetrahydropyrrolo[2,3-b]indole-3-carboxylate from Step-2.
weight: 10
criterion: Does the response correctly identify the application of N-Methylation mechanism in step 3?
weight: 10
criterion: Correct identification of compound C as methyl (3aR,8aR)-1,3a,8-trimethyl-1,3a,8,8a-tetrahydropyrrolo[2,3-b]indole-3-carboxylate from Step-3.
weight: 10
criterion: Does the response correctly identify the molecular formula of the final product as \(C_{15}H_{18}N_2O_2\)?
weight: 20
criterion: Does the final answer explicitly state the molecular weight of the major product (Compound C) as $258.32 \ \text{g/mol}$ ?
weight: 20

Answer:
258.32 g/mol