See image — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the substrate: The starting material is a bicyclic compound consisting of a cyclohexane ring fused to an oxetane (a 4-membered cyclic ether) at two adjacent carbons of the cyclohexane. This is 1-oxaspiro or, more precisely, a fused bicyclic oxetane: 2-oxabicyclo[4.2.0]... actually it is the oxetane fused to cyclohexane, i.e., the oxygen bridges two adjacent carbons of cyclohexane forming a 4-membered ring (oxetane). Step 2 - Reaction with Grignard reagent (CH3MgI): Grignard reagents open strained cyclic ethers. Oxetanes are more reactive than THF but less reactive than epoxides. CH3MgI (methylmagnesium iodide) acts as a nucleophile (CH3-) and attacks the less hindered carbon of the oxetane ring (the exocyclic -CH2- of the oxetane, i.e., the carbon not part of the cyclohexane ring), breaking the C-O bond. Step 3 - Regioselectivity: In the fused bicyclic oxetane, one carbon of the oxetane is part of the cyclohexane ring (more substituted, tertiary-like) and the other is the exocyclic CH2 (less substituted). Grignard nucleophiles attack the less hindered carbon (SN2-like), which is the exocyclic CH2 of the oxetane. Step 4 - Product formation: Attack of CH3- at the exocyclic CH2 opens the C-O bond. The oxygen remains bonded to the cyclohexane carbon. After aqueous workup (H3O+), the alkoxide is protonated to give an alcohol. The product has: the cyclohexane carbon bearing -OH (from the oxetane oxygen) and a -CH2CH3 substituent on the adjacent carbon (CH3 added to CH2 gives -CH2-CH3... wait, let me reconsider: CH3- attacks the -CH2- carbon of the oxetane, giving -CH2-CH3 attached to the ring carbon, and the O stays on the cyclohexane carbon as -OH after protonation). Step 5 - Structure of product: The result is a cyclohexane with -OH on C1 and -CH2CH3 on C2, which matches option (b): 1,2-disubstituted cyclohexane with OH at one ring carbon and CH2-CH3 at the adjacent ring carbon. Step 6 - Why other options fail: - (a) shows CH3 and CH2OH substituents - this would require attack at the ring carbon with retention of a hydroxymethyl, inconsistent with simple Grignard opening. - (c) shows an O-CH3 (ether) product - Grignard reagents don't form ethers; they give alcohols after protonation. - (d) shows a fused cyclobutane with OH and CH3 - the ring is not retained; the C-O bond breaks on ring opening. Therefore, the correct answer is B.