The Lemieux–Johnson oxidation is an organic reaction that cleaves the carbon–carbon double bond (C=C) of an alkene. During the reaction, each carbon of the original double bond forms a carbonyl (C=O) group. Depending on the groups attached to the original alkene, the products can be aldehydes, ketones, or a combination of both. ^[1–3]

The reaction was reported by Pappo, Allen, Lemieux, and Johnson in 1956.

General Reaction

The overall transformation can be represented as: ^[1,2]

R¹R²C=CR³R⁴  —[OsO₄, NaIO₄]→  R¹R²C=O + O=CR³R⁴

The two important changes are:

• The C–C bond between the two original alkene carbons is broken.
• A C=O bond forms at each of these carbons.

The two carbons of the original C=C bond therefore become the carbonyl carbons of the products.

The type of carbonyl compound formed depends on the groups originally attached to each alkene carbon:

• If an alkene carbon has a hydrogen atom, it becomes the carbonyl carbon of an aldehyde.
• If an alkene carbon has no hydrogen atom and is attached to two carbon groups, it becomes the carbonyl carbon of a ketone.

This rule can be used to predict the products in the following examples.

Examples

Mechanism

The Lemieux–Johnson oxidation can be understood in terms of two main transformations. First, osmium tetroxide (OsO₄) converts the alkene into a vicinal diol. Periodate then cleaves the carbon–carbon bond of the diol, forming carbonyl compounds. ^[3,4]

The overall sequence can therefore be summarized as:

Alkene → Vicinal diol → Carbonyl compounds

A commonly used simplified mechanism is shown below.

Step 1: Formation of a Vicinal Diol

OsO₄ reacts with the alkene to form a cyclic osmate ester. Hydrolysis of this intermediate produces a vicinal diol, with two –OH groups on neighboring carbon atoms.

Step 2: Formation of a Cyclic Periodate Ester

The vicinal diol reacts with periodate (IO₄^–) to form a cyclic periodate ester.

Step 3: Carbon–Carbon Bond Cleavage

The cyclic periodate ester fragments. The C–C bond between the two hydroxyl-bearing carbons breaks, and a C=O bond forms at each carbon.

The resulting products are aldehydes, ketones, or a combination of both, depending on the structure of the original alkene.