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A six-membered oxygen-containing ring with one double bond (dihydropyranyl system) bearing an O2N (nitro) substituent reacts in DMSO at 80 degrees C with a benzene ring that has adjacent OH and CH2Br substituents. Which of the following statements about this reaction are correct?

1. The major product is a fused tricyclic compound formed by intramolecular cyclization
2. The reaction proceeds via nucleophilic substitution
3. DMSO acts as a base in the reaction
4. The reaction involves electrophilic aromatic substitution

Correct answer: The reaction proceeds via nucleophilic substitution

Solution

The phenolic OH acts as a nucleophile and displaces Br from the CH2Br group via SN2, forming a new C-O bond. DMSO is a polar aprotic solvent that stabilizes the transition state but does not act as a base.

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