Expanding the Chemical Space of 1,2-Difunctionalized Cyclobutanes.

An efficient approach to the synthesis of previously unavailable or hardly accessible 1,2-difunctionalized cyclobutanes (mostly with NH 2 /NHBoc, OH, SH, or SO 2 F groups attached to the carbocycle either directly or via a CH 2 unit) relying on the divergent strategy is described. This class of compounds provides sp 3 -enriched and conformationally restricted building blocks that are of special demand for medicinal chemistry. The target compounds were prepared not only as pure racemic (±)- cis - and (±)- trans -diastereomers but in some cases also as single enantiomers. The developed procedures are readily scaled up and allow obtaining the target compounds on an up to hundred-gram scale. On the basis of the results of 20 X-ray diffraction experiments, structural characterization of the 1,2-difunctionalized cyclobutane core was performed using the extended Cremer-Pople puckering parameters and exit vector (EVP) plots.