Mechanism of 1,2-epoxycyclopentane to Trans-2-Methylcyclopentanol

Question

Help draw a reasonable mechanism for Reaction of 1,2-epoxycyclopentane to Trans-2-Methylcyclopentanol with 1. CH₃MgBr/ 2. H₃O⁺ as reagents.

Answer 1

This is a picture of how the reaction proceeds:

The reaction of Me–MgBr with the epoxide is an S_N2 reaction, so

1. backside attack
2. inversion of configuration

leading to the trans relationship between the Me and OH groups in the product.