Synthesis and conformation of chiral biheteroaryls

Bridging 2,3 and 2',3' positions in 2,2'-dihydroxy-1,1'-binaphthyl and 2,2'-diamino-1,1'-binaphthyl, respectively, resulted in formation of chiral O- and N-bis-tricyclic compounds accessible in 4 steps from known 3,3'-diiodo precursors. In both cases, 2-fold ring closing metathesis of tetraallyl intermediates proceeded regioselectively to give tetrahydrobinaphtho[2,3-b]oxepine and -azepine, respectively. In case of the N-mesyl-N-allyl precursor, three, at room temperature separable, rotamers were isolated and characterized by NMR spectroscopy and X-ray structure determination. Their interconversion (process I) was followed by NMR, yielding rate constants and thermodynamic parameters. The rotamers with either C(1) or C(2) symmetry were stereospecifically cyclized to conformatively moderately stable bis-sulfonamides. Also in this case, the kinetics of their interconversion (process II) was investigated and from two of them the crystal structure was determined. Processes I and II were investigated by a DFT method, M06-2X, to gain insight into electronic and steric peculiarities responsible for the remarkable conformative stabilities. Transition state geometries and energies were calculated and compared with empirical data.