See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the starting material: The substrate is an ortho-substituted cyclohexene (drawn as a benzene-like ring with a circle, but likely a cyclohexene or benzene ring) bearing two substituents at adjacent positions: (i) a 1-bromovinyl group, -C(Br)(=CH2), at one carbon and (ii) a hydroxymethyl/secondary alcohol group, -CH(OH)-, at the adjacent carbon. Step 2 - Role of NaOH: NaOH is a base that deprotonates the alcohol group (-OH) to generate an alkoxide (-O-), which is a powerful intramolecular nucleophile. Step 3 - Intramolecular SN2 or substitution reaction: The alkoxide oxygen, generated from the adjacent -CH(OH)- group, is perfectly positioned to attack the carbon bearing the bromine in an intramolecular fashion. The carbon bearing Br is a vinyl carbon (part of C(Br)=CH2), making it a vinylic system. However, considering the geometry, the alkoxide attacks the sp2 carbon bearing the bromine (vinylic substitution) or the reaction proceeds via an epoxide/three-membered ring intermediate, ultimately forming a five-membered oxygen-containing ring (dihydrobenzofuran skeleton). Step 4 - Product formation: The intramolecular cyclization of the alkoxide onto the C-Br carbon displaces bromide and forms a new C-O bond, creating a five-membered ring (furan ring) fused to the benzene/cyclohexene ring. The =CH2 group becomes =C(CH3)- (or remains as exocyclic alkene =CH2 becoming part of the ring), resulting in a 2,3-dihydrobenzofuran system with an exocyclic methylidene or isopropylidene group. The product is a dihydrobenzofuran with a =C(CH3) substituent, matching option (b). Step 5 - Why other options fail: - Option (a): Simple hydrolysis replacing Br with OH would give a diol, but intramolecular cyclization is strongly favored when a nucleophile and electrophile are on adjacent carbons. - Option (c): This would require a rearrangement to give an allylic alcohol without cyclization, which is not the expected pathway under basic conditions. - Option (d): A six-membered ring (chromene) would require a 1,3-relationship between the OH and C-Br, but here they are on adjacent carbons (1,2-relationship), which favors five-membered ring formation. Therefore, the correct answer is B.