A new chemoselective base-mediated protection/deprotection method for aldehydes

A wide range of aldehydes was efficiently protected as pyrrole carbinol derivatives by direct addition of lithium pyrrolate in THF at -78 degreesC. The protection is chemoselective towards aldehydes over ketones and the O-lithiated, O-protonated or O-silylated carbinols may be used to block the aldehyde from nucleophilic and basic reagents at low temperatures. Mild, basic deprotection using DBU, NaOMe or TBAF allows for in situ trapping-reactions (such as Wadsworth-Homer-Emmons olefination) of the released aldehyde.