A-silyloxy carbanions

Rearrangement of a-silyl oxyanions to a-silyloxy carbanions via a reversible process involving a pentacoordinate silicon intermediate is known as the [l,2]-Brook rearrangement, or [l,2]-silyl migration. 

The relative ease of pinacolization is primarily determined by the reduction potential of the carbonyl group involved. Many reductants are therefore selective for aromatic and other electronically activate systems. Moreover, as a result of this ready reduction, pinacolization of such carbonyls can be effected by either anionic or radical routes. For example, treatment of aromatic aldehydes or ketones with Mg/TMSCl in HMPA promotes pinacolization via formation of an a-silyloxy carbanion - and nucleophilic attack on a second carbonyl group (equation 2). Furthermore, with benzaldehyde the reaction is stereodirecting with a preference for /it-coupling. Whilst an alternate coupling metht using the milder... 

---

See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

---