Oxy-Cope Rearrangement

Definition

The oxy-Cope rearrangement is a sigmatropic rearrangement reaction that involves the migration of a hydrogen atom and a substituent group between the termini of a conjugated triene system. It is a key example of the broader class of sigmatropic rearrangements discussed in Section 30.8.

5 Must Know Facts For Your Next Test

1. The oxy-Cope rearrangement is a variant of the Cope rearrangement, where an oxygen atom is present in the 1,5-diene system.
2. The rearrangement proceeds through a chair-like transition state, where the migrating hydrogen atom and substituent group are in a pseudo-equatorial orientation.
3. The oxy-Cope rearrangement is often used in the synthesis of complex natural products, as it allows for the construction of new carbon-carbon bonds and the introduction of oxygen functionality.
4. The reaction is typically promoted by the presence of Lewis acidic catalysts, which can stabilize the transition state and lower the activation energy.
5. The stereochemistry of the starting material and the transition state geometry dictate the stereochemical outcome of the oxy-Cope rearrangement.

Review Questions

• Explain the key features of the oxy-Cope rearrangement and how it differs from the standard Cope rearrangement.
  • The oxy-Cope rearrangement is a variant of the Cope rearrangement, where an oxygen atom is present in the 1,5-diene system undergoing the sigmatropic rearrangement. Like the Cope rearrangement, the oxy-Cope rearrangement involves the migration of a hydrogen atom and a substituent group between the termini of the conjugated triene system. However, the presence of the oxygen atom can influence the reaction mechanism, transition state geometry, and stereochemical outcome of the rearrangement. The oxy-Cope rearrangement is often used in the synthesis of complex natural products, as it allows for the construction of new carbon-carbon bonds and the introduction of oxygen functionality.
• Describe the transition state of the oxy-Cope rearrangement and explain how the presence of a Lewis acidic catalyst can affect the reaction.
  • The oxy-Cope rearrangement proceeds through a chair-like transition state, where the migrating hydrogen atom and substituent group are in a pseudo-equatorial orientation. This transition state geometry is stabilized by the conjugation of the triene system and the presence of the oxygen atom. The addition of a Lewis acidic catalyst, such as a metal ion or a Lewis acidic compound, can further stabilize the transition state by coordinating to the oxygen atom. This coordination can lower the activation energy of the rearrangement, making the reaction more favorable and potentially improving the yield and selectivity of the transformation.
• Analyze the importance of the oxy-Cope rearrangement in organic synthesis and discuss how the stereochemistry of the starting material and transition state geometry can impact the stereochemical outcome of the reaction.
  • The oxy-Cope rearrangement is a powerful tool in organic synthesis, as it allows for the construction of new carbon-carbon bonds and the introduction of oxygen functionality in a single step. The stereochemistry of the starting material and the transition state geometry are crucial factors that determine the stereochemical outcome of the rearrangement. The chair-like transition state of the oxy-Cope rearrangement favors the migration of the hydrogen atom and substituent group in a stereospecific manner, leading to the formation of new stereogenic centers. By carefully designing the starting material and controlling the reaction conditions, organic chemists can leverage the oxy-Cope rearrangement to synthesize complex natural products and other target molecules with high levels of stereochemical control.

Related terms

Sigmatropic Rearrangement: A sigmatropic rearrangement is a pericyclic reaction in which a $\sigma$-bond migrates to a new position within the same molecule.

Cope Rearrangement: The Cope rearrangement is a [3,3]-sigmatropic rearrangement of a 1,5-diene system that involves the migration of a hydrogen atom and a substituent group.

Conjugated Triene: A conjugated triene is a system of three consecutive carbon-carbon double bonds, where the $\pi$-orbitals overlap to create a continuous network of delocalized electrons.