Stereocontrolled Preparation of Diversely Trifunctionalized Cyclobutanes.

The expedient and stereoselective syntheses of small libraries of trifunctionalized cyclobutane scaffolds bearing an acid, an amine, and a third functional group are described. Starting from a single precursor, the readily available protected derivative of -2-amino-3-hydroxycyclobutane-1-carboxylic acid, stereoisomers are obtained following an S2-type reaction, while stereoisomers are obtained using the same strategy preceded by a C1 epimerization reaction.