Transamidation expansion

A total synthesis of (+)-dihydroperiphylline (27) has been achieved, starting from piperidazine and utilising a ring-expansion reaction by a transamidation with the imino-ether (28) and a /Mactam.21 This procedure has also been used to synthesize celacinnine.22... 

Scheme VI/7. The transamidation reaction as a repeatable ring expansion process [30].

Several substituted fi-lactams and benzyl amine derivatives participated in this coupling reaction, though the ring expansion was slower when /V-substituted benzyl amines were used. Exposure of the intermediate /V-aryl lactam to AcOH in THF, however, overcame the sluggish transamidation. In some examples, the addition of N,N -dimethylethylene-diamine facilitated the reaction, though it was not required in all cases. Phenethyl amine 672 reacted with azetidinone 670 to give 673 in 78% yield. 

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