Amino group migration synthesis with

The regiochemical course reacting saturated ketones depended on the substitution pattern of the a-positions. In most cases, the intermediate oxime had an anti N-OH function with respect to the chain branched a-position. Consequently, the more substituted alkyl group preferentially migrates. This advantage was utilized for synthesizing the spiro a-amino-e-caprolactam (202 203, Scheme 38) [12c], the Mexican bean beetle azamacrolide allomone (205 206, Scheme 39) [44 a], in a key step of the chiral synthesis of benzomorphanes... 

In the synthesis of a-amino acids [290] through addition of the carbanion of MMTS to nitriles the overall process involves three other steps frequently encountered in sulfur-mediated chemistry a Pummerer-type rearrangement, with a less common migration of a methylthio group, and a Raney nickel desulfurization following transesterification of the thioester function. 

Fig. 6.15. Carboxylic acid activation with DCC. [1,3] means the intramolecular substitution of the oxygen atom 01 by the N atom "3" via a cyclic four-membered tetrahedral intermediate. From the point of view of the heteroatoms, this SN reaction corresponds to a migration of the acyl group R-C=0 from the oxygen to the nitrogen. (Examples for amino acid activations in the form of the pentafluorophenyl ester C or the benzotriazolyl ester D are given in Figure 6.32 (oligopeptide synthesis) and Figure 6.31 (dipeptide synthesis), respectively.

---