Brook rearrangement

The rearrangement was first observed in the late 1950s by Canadian chemist Adrian Gibbs Brook (1924–2013), after which the reaction is named.

Depending on the relative stabilities of the carbanion and oxy-anion formed, a silyl ether is perfectly capable of rearranging to a species with the silicon bonded to the carbon atom, and the free alcohol being present.

This can then undergoes intramolecular attack by the oxy-anion to yield the silyl ether, but the final fate of the carbanion often depends on the substrate in question.

For example, attempting to perform a Wittig reaction on acylsilane results in the formation of a silyl enol ether instead of the expected alkene, due to elimination by the carbanion instead of protonation as seen above.

The Brook rearrangement has been shown to occur with retention of configuration at the silicon center as demonstrated in the following Walden cycle: All steps in this cycle were known to proceed with retention of configuration except for attack of the lithium reagent (which proceeded by inversion) and the Brook Rearrangement, which was being investigated.

By starting with a chiral silicon of known configuration, the stereochemistry of the reaction could be determined by looking at the specific rotation of the recovered silane.

Experimentally, the recovered silane was the opposite enantiomer, showing that the reaction occurred with retention at the silicon center.