Conformational strain, lactams

Nine-membered rings are strained in all of their conformations. Conformational studies of saturated heteronines and heteronines containing torsional constraint caused by double bonds, three-membered and benzo-annulated rings, lactams and lactones were the part of the survey <1999MI(5)89>. 

The planar cis-amide conformation in the seven-membered lactam already can impose some strain on the ring and thus increase its polymerizability. 

As a rule, the synthesis of -lactams by cyclization of -amino acids such as (132) is impeded by Bayer strain and adverse conformational effects." By contrast, the conversion of 3-amino acids into p-lactams by the Ugi reaction occurs with ease and in good yield. " ... 

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