Oxy-Cope Rearrangement

The oxy-Cope rearrangement is a pericyclic reaction that involves the migration of a hydroxyl group and a hydrogen atom from one end of a conjugated diene to the other. This rearrangement results in the formation of a new double bond and a new carbonyl group. The reaction is named after Arthur C. Cope, who first observed this reaction in 1947.

Mechanism:

The reaction mechanism of oxy-Cope rearrangement can be explained in the following steps:

1. A hydroxyl group attacks the conjugated diene from the less hindered side, forming a cyclic intermediate.

2. The cyclic intermediate then undergoes a 1,5-hydrogen shift, which results in the migration of the hydroxyl group and a hydrogen atom from one end of the conjugated diene to the other.

3. The resulting intermediate then undergoes a ring-opening step, which forms a new carbonyl group.

4. Finally, the double bond migrates to the opposite end of the conjugated diene, resulting in the formation of a new double bond.

Applications:

The oxy-Cope rearrangement has been extensively used in organic synthesis to generate complex molecules with multiple chiral centers. It has also been used in the synthesis of natural products such as steroids, alkaloids, and terpenes.

Examples:

1. The conversion of 1,5-hexadiene to 2-pentanone:

2. The conversion of 1,5-hexadiene to 2-methyl-3-pentanone:

In both examples, the oxy-Cope rearrangement results in the formation of a new carbonyl group and a new double bond. The reaction is particularly useful in the synthesis of ketones and aldehydes with specific stereochemistry.