Diastereoselective Amidoboronate Formation and Transformation from a rac to a Different meso Amidoboronate via Dynamic C-C Bonds

Amidoboronates synthesized through the reductive coupling of iminoboronates with cobaltocene in DMSO formed as mixtures of up to three isomers (rac5, rac6 and meso5) and in some cases, a cobaltocene derivative from two-electron reduction. The amidoboronate product distribution depended on the aniline, catechol and boronic acid subcomponents of the iminoboronate substrate; diastereoselective rac isomer formation was observed for amidoboronate 5e (based on p-NMe2-substituted aniline, pyrocatechol and phenylboronate), whereas employing an iminoboronate containing p-OMe-substituted aniline, either pyro- or tetrachlorocatechol and 3 fluorophenylboronate led to rare examples of meso diastereoselectivity (9:1 dr for 7d and 8d). The addition of a second iminoboronate to amidoboronate reaction mixtures probed the reversibility of C C bond formation as evidenced by the formation of new homo- and cross coupled amidoboronates via exchange. The dynamic covalent C-C bonds were exploited in the unprecedented diastereoselective transformation of rac5/6-5e to meso5-7d following addition of excess iminoboronate 3d.