The regiospecific lithiation of aromatic acetals

✍ Scribed by H.P. Plaumann; B.A. Keay; R. Rodrigo

• Publisher: Elsevier Science
• Year: 1979
• Tongue: French
• Weight: 189 KB
• Volume: 20
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(01)86750-2

✦ Synopsis

The dimethylacetal of benzaldehyde and some 3, 3,4 and 3,4,5 oxygenated derivatives thereof are regiospecifically deprotonated at the 2-position by alkyl lithiums. The resulting aryl lithiums provide various 2-substituted benzaldehydes in moderate to excellent yields.

Following the pioneering work of Hauser, several investigators have established that regiospecific deprotonation of aromatic systems ortho to an existing substituent may be accomplished with alkyl lithiums. The success of these 'ortho-lithiations' have been attributed in the main to intramolecular coordination of the lithium with a lone pair of electrons in the substituent.

A great variety of such ortho-directing substituents have been employed,2 but among these only one report' involved the use of a modified aromatic aldehyde. In that instance the cyclohexylimine of piperonal was observed to deprotonate at the 2-nosition exclusively, and the resulting 2-lithio