The effect of sulphur dioxide on the mannich reactions of phenols

✍ Scribed by Robin A. Fairhurst; Harry Heaney; George Papageorgiou; Robert F. Wilkins

• Publisher: Elsevier Science
• Year: 1988
• Tongue: French
• Weight: 249 KB
• Volume: 29
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)82196-6

✦ Synopsis

Smmary: Regioselectivity in the ortho-dialkylaminomethylation of phenols is greatest, for example in reactions of 2,5_dimethylphenol, when a mixture of the phenol and sulphur dioxide is allowed to stand for several hours before the addition of a bis-(dialkylamino)methane (aminal) or an alkoxydialkylaminomethane (amino1 ether).

Recently we reported1 that sulphur dioxide may be used as a reagent with aminals and amino1 ethers in Mannich reactions of a number of heterocycles. We report now that phenols react and afford, under favourable conditions, high yields of 2-dialkylaminomethylphenols.

Mannich reactions of phenols have been studied on many occasions and in the majority of cases ortho-monosubstitution predominates.

2 The precise mechanism involved depends on the reaction