Reaction of acetals with various carbon nucleophiles under non-acidic conditions: C-C bond formation via a pyridinium-type salt

Mild substitution reactions of acetals with carbon nucleophiles via the pyridinium-type salts generated by the treatment of acetals with TESOTf-2,4,6-collidine or 2,2′-bipyridyl have been developed. Various carbon nucleophiles, such as organocuprates, silyl enol ethers, enamines, etc., reacted with the pyridinium-type salts to give the corresponding substituted products in good yields. The reactions proceeded under very mild conditions (non-acidic conditions) and thus acid-sensitive functional groups can be tolerated during the reaction. In addition, only an acetal can form the pyridinium-type salt and react with nucleophiles in the presence of a ketal. This unusual selectivity is in contrast to general methods conducted under acidic conditions. Salty but sweet: Pyridinium-type salts generated from acetals are effective electrophiles for various carbon nucleophiles. The reactions proceed under very mild (non-acidic) reaction conditions and can tolerate acid-sensitive functional groups (see scheme).