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, e-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 .e-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.