New Strategies for Sulfate-Free Synthesis of Lactams from Cycloalkanes Using NHPI as a Key Catalyst

Abstract

New strategies for lactams synthesis from cycloalkanes without formation of sulfates have been proposed. The synthesis of lactams from cycloalkanes through a one-pot reaction was successfully performed using N-hydroxyphthalimide (NHPI) as a key catalyst. The strategy involves nitrososation of cycloalkanes with tert-butyl nitrite under the influence of NHPI followed by isomerization to oximes and then the Beckmann rearrangement to lactams. For example, ε-caprolactam and laurolactam were prepared from cyclohexane and cyclododecane in 74% and 78% yields, respectively, in one-pot. An alternative approach for sulfate-free lactam synthesis includes the nitration of cyclohexane with NO₂ to nitrocyclohexane in the presence of NHPI under mild conditions followed by the hydrogenation to cyclohexanone oxime. The Beckmann rearrangement to .ε-caprolactam was found to be achieved in quantitative yields by a very small amount of cyanuric chloride in a mixed solvent of trifluoroacetic acid and toluene.