Beckmann rearrangement of oxime obtained from oleanolic acid. Structure elucidation of the initial oxime

Seven-membered A-lactam and A-nitrile of methyl oleanolate were synthesized from the corresponding oxime. Many reaction setups were tried to find the optimum conditions. The best results (the highest yield of the desired lactam along with total consumption of starting oxime) were obtained in pyridine with phosphoryl chloride as Lewis acid. The main product was obtained with the yield of about 60%. Mechanism of Beckmann rearrangement for the above triterpenic 3-oxime leading to normal and abnormal product (a lactam and a nitrile, respectively) was explained. The structures of both products were determined and fully characterized by spectral data. The stereoisomerism of the initial oxime was determined on the basis of Beckmann rearrangement product structure and X-ray analysis.