| Summary: | In recent years, our group has been involved in the use of the Ugi-Passerini reaction for the synthesis of several alpha,alpha-dialkylglycines. The C-terminal amide bond of the resulting Ugi adducts 1 proved to be very sensitive to TFA, cleaving readily by a mechanism involving an oxazolinium-type intermediate 2. This intermediate allows in situ functionalization of the C-terminus by reaction with several nucleophiles, affording different derivatives such as free acids, esters and amides. Our previous results suggested that a dipeptide could be obtained if an amino acid ester was used as the nucleophile. The results obtained so far indicate that although a small amount the required dipeptides 3 is formed, 5,5-dialkyl-imidazolin-4-ones 4 are the major products. These may result from competitive attack at the less hindered C-2 of the oxazolinium intermediate, followed by rearrangement.
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