Grignard reagent + epoxide template

Phenylmagnesium bromide opens (R)-2-methyloxirane at the CH₂ carbon (SN2); the stereocentre is not touched, and acid work-up gives (R)-1-phenylpropan-2-ol.

Mechanism step by step

SN2 at the less hindered carbon; the alcohol is two carbons from the new C–C bond

1. Ring opening (SN2) – The C–Mg bond attacks the less hindered CH₂; the C–O bond breaks and the strain is released
2. Acid work-up – Protonation gives the secondary alcohol

Key points

• A strong, basic carbon nucleophile opens the strained ring by SN2 at the less hindered carbon; the substituted stereocentre keeps its configuration.
• Attack at a stereocentre inverts it: cyclohexene oxide gives trans-2-substituted cyclohexanols.
• Ethylene oxide + RMgX → RCH₂CH₂OH, a two-carbon chain extension (formaldehyde adds one carbon).
• MgBr₂ is a Lewis acid that can rearrange epoxides to carbonyl compounds, so a little Cu(I) (or a cuprate) is often used for clean opening.

Drawn with 69 atoms, 7 arrows, 8 shapes – every one editable in MolDraw.

Sources

• Clayden, Greeves & Warren, Organic Chemistry, 2nd ed., OUP 2012, ch. 15 Textbook
• Smith, March's Advanced Organic Chemistry, 8th ed., Wiley 2020, ch. 10 Textbook