Synthesis of N-acyl-N,alpha,alpha-trialkyl and N-acyl-alpha,alpha-dialkyl glycines by selective cleavage of Ugi-Passerini adducts. Qualitative assessment of the effect of substituents on the path and yield of reaction

Several symmetric N-acyl-N,alpha,alpha-trialkyl glycine amides were synthesised by the Ugi-Passerini four-component reaction and subjected to selective cleavage with trifluoroacetic acid. In almost all cases it was possible to obtain the corresponding N-acyl-N,alpha,alpha-trialkyl and N-acyl-alpha,alpha-dialkyl glycines in fair to good yields directly from the reaction adducts. With some of the bulkier compounds our results show that the selectivity of cleavage is concentration dependent with respect to the acid, which suggests kinetically controlled processes. The isolation of a stable oxazolone as the product of some of the reactions seems to confirm that amide cleavage involves in all cases formation of an oxazolone-type derivative.