Master Organic Chemistry Reaction Guide

Addition of Grignard reagents to ketones to give tertiary alcohols

Description: When a ketone is treated with a Grignard reagent, a new C–C bond is formed at the carbonyl carbon. Subsequent addition of acid will then give the alcohol.

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Real-Life Examples:

Org. Synth. 1937, 17, 89

DOI Link: 10.15227/orgsyn.017.0089

Click to Flip

Org. Synth. 1944, 24, 84

DOI Link: 10.15227/orgsyn.024.0084

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Comment section

8 thoughts on “Addition of Grignard reagents to ketones to give tertiary alcohols

  1. Hi James,
    Is there a rule for stereochemistry when adding a grignard? For instance, in example 1 and 2, would the stereocenter default to R or S?

    1. “Conservation of optical inactivity”. If there’s no chiral influence on a reaction, the product of an achiral starting material with an achiral reagent will result in an optically inactive product. A racemic mixture of enantiomers, in other words.

  2. Hmm… Does Grignard react with hydrogen of alpha carbon?? Because that hydrogens are acidic, isn’t it??

    1. Addition is faster than deprotonation. The C-H is only really acidic when aligned at 90° to the carbonyl, and deprotonation also involves considerable reorganization of atomic geometry (see: principle of least motion). For non-hindered ketones, addition is considerably faster. This can change for sterically hindered ketones, however…

    1. That’s because #4 is a trick question! Acid base reactions are fast, relative to Grignard addition – the Grignard reacts with the carboxylic acid in an acid-base reaction, and the carboxylic acid is later protonated with acid workup. Very common trick question!

  3. Question! In the 3rd flip/quiz example, you have 9 carbons to work with and end up with 10. How/why? Thanks!

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