Preparation of Conformationally Restricted β2,2- and β2,2,3-Amino Esters and Derivatives Containing an All-Carbon Quaternary Center

beta-Amino acids are routinely incorporated into peptidic drugs to increase their stability and to incur conformational biases. However, the synthesis of highly substituted beta-amino acids still represents a great challenge. A new approach to their preparation is reported involving a VilsmeierHaack reaction with nonaromatic carbon nucleophiles. The highly challenging preparation of contiguous tertiary and all-carbon quaternary centers was successfully used to generate several beta(2,2,3)-amino esters, such as derivatives of homoproline, homoalanine, and homopipecolinic esters.