Asymmetric Ni(II)/Cr(II)-mediated coupling reaction: Stoichiometric process

[GRAPHICS] Via an X-ray analysis, the sulfonamide bearing R-1 = i-Pr, R-2 = Me, and R-3 = Me is shown to be a tridentate ligand to a Cr(III) salt. This class of ligands, represented by R-1 = t-Bu, R-2 = 2-naphthyl, and R-3 = Me, is effective to achieve an asymmetric NI/Cr-mediated coupling reaction and, with the C14-C38 segment of halichondrins, its synthetic potential has been demonstrated. A possible mechanism is suggested for the process.