Brook Rearrangement
The rearrangement of silicon groups from any [1,n] carbon to oxygen is called the Brook rearrangement. These migrations can occur thermally, photolytically or under basic/acidic conditions. In the forward direction, these silyl migrations produce silyl ethers as products which is driven by the stability of the oxygen-silicon bond.
The silyl substituents can be aliphatic or aromatic, and if the silicon is a Chiral center, the migration occurs with retention at this center. This migration occurs through a transition state where silicon is penta-coordinate and bears a partial negative charge. If a center of chirality is present at the carbon center to which the silyl group is attached, then inversion occurs at this center.
The greater strength of the oxygen-silicon bond compared to the carbon-silicon bond provides the driving force for the conversion of silyl carbinols to the corresponding silyl ethers. An electron-withdrawing R group facilitates the kinetics of the carbanion formation.
Rearrangement of α-silyl oxyanions to α-silyloxy carbanions via a reversible process involving a pentacoordinate silicon intermediate is known as the [1,2]-Brook rearrangement, or [1,2]-silyl migration.
The silyl substituents can be aliphatic or aromatic, and if the silicon is a Chiral center, the migration occurs with retention at this center. This migration occurs through a transition state where silicon is penta-coordinate and bears a partial negative charge. If a center of chirality is present at the carbon center to which the silyl group is attached, then inversion occurs at this center.
Mechanism of Brook Rearrangement
The possible mechanism is given below-The greater strength of the oxygen-silicon bond compared to the carbon-silicon bond provides the driving force for the conversion of silyl carbinols to the corresponding silyl ethers. An electron-withdrawing R group facilitates the kinetics of the carbanion formation.
Applications of Brook Rearrangement
Rearrangement of α-silyl oxyanions to α-silyloxy carbanions via a reversible process involving a pentacoordinate silicon intermediate is known as the [1,2]-Brook rearrangement, or [1,2]-silyl migration.
