= Solution
The terminal alkene of D first undergoes <Wacker oxidation>, giving the side chain $\mathrm{Ar-CH_2-CH_2-COCH_3}$. Alkene coordination to Pd(II), water attack, <proton transfers> and <beta-hydride elimination> give the <ketone>. Copper and oxygen regenerate the active palladium oxidation state.
Base removes a <proton> from the terminal methyl of that <ketone>. Its <enolate> attacks the neighboring aromatic aldehyde intramolecularly, closing a six-membered ring. Dehydration gives a conjugated cyclohexadienone-type intermediate, and <keto-enol tautomerism> furnishes aromatic naphthol E. The retained methoxy and MOM-protected oxygen groups follow the original aromatic-carbon positions.
\b[F is the O-allyl ether of E.] Carbonate forms the naphthoxide and allyl bromide undergoes an <SN2 reaction> at its terminal carbon. Heating F then causes a \[3,3\]-<Claisen rearrangement>: the O–allyl bond breaks, the terminal allyl carbon bonds to the adjacent naphthalene C1, and the phenolic carbon temporarily becomes a <ketone>. Rearomatization gives G, with a free phenolic OH and a C1 allyl group. The C1 position gives the favored alpha-substituted naphthol and avoids the alternative less favorable annulation pattern.
The final step is a \b[dearomative <Michael addition>], not a Nef conversion of the nitro group. Hydrogen bonding from the thiourea activates nitroethylene. The nucleophilic C1 resonance form of G attacks the terminal carbon of $\mathrm{CH_2=CHNO_2}$, and <proton transfer> converts the nitronate to a 2-nitroethyl substituent. The phenolic carbon becomes a <ketone>.
\b[H is the corresponding 1-allyl-1-(2-nitroethyl)naphthalen-2-one], retaining the methoxy and MOM substituents of G. The second ring now has a C2=O group and a C3=C4 bond, while the other ring remains aromatic. The reported $^{13}$C signal near $202$ ppm is consistent with that newly formed <ketone>. Related dearomative additions establish this reaction class.<Asymmetric Dearomatization of β-Naphthols through a Bifunctional-Thiourea-Catalyzed Michael Reaction by Shou-Guo Wang and others>[Abstract, addition of nitroethylene to alpha-substituted beta-naphthols]{ref}
C1 is now an all-carbon quaternary <stereocenter> bearing both allyl and 2-nitroethyl groups. Both the drawn thiourea and the starting materials are achiral, so \b[H is racemic]. A chiral <catalyst> would be needed to select one absolute configuration.
\Image[/past-exam-of-the-chemistry-course-of-the-year-4-of-the-natural-sciences-course-of-the-university-of-cambridge/2022/paper-1-naphthol-products.png]
{title=O-allyl intermediate and dearomative Michael-addition product}
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