Synthesis of new cyano-substituted analogues of Tröger's bases from bromo-derivatives. A stereochemical dependence of long-range (nJHH, n = 4, 5, and 6) proton–proton and proton–carbon (nJCH, n = 1, 2, 3, 4, and 5) coupling constants of these compounds

RAMIREZ, CRISTINA; VERA, D. MARIANO; AKHMEDOV, NOVRUZ G.; PARISE, ALEJANDRO; CHESTA, CARLOS; DUSSO, DIEGO; LANZA, P.; MOYANO, E. LAURA

MAGNETIC RESONANCE IN CHEMISTRY

JOHN WILEY & SONS LTD

Año: 2019 vol. 57 p. 423 - 454

0749-1581

A free-catalyst microwave-assisted cyanation of brominated Tröger´s base derivatives (2a-f) is reported. The procedure is simple, efficient, and clean affording the nitrile compounds (3a-e, I) in very good yields. Complete assignment of 1H and 13C chemical shifts of 2a-f, I and 3a-d, I was achieved using gradient selected 1D nuclear magnetic resonance (NMR) techniques (1D zTOCSY, PSYCHE, DPFGSE NOE, and DEPT), homonuclear 2D NMR techniques (gCOSY and zTOCSY), and heteronuclear 2D NMR techniques (gHSQCAD/or pure-shift gHSQCAD, gHMBCAD, bsHSQCNOESY, and gHSQCAD-TOCSY) with adiabatic pulses. Determination of the long-range proton?proton coupling constants nJHH (n = 4, 5, 6) was accomplished by simultaneous irradiation of two protons at appropriate power levels. In turn, determined coupling constants were tested by an iterative simulation program by calculating the 1H NMR spectrum and comparing it to the experimental spectrum. The excitation-sculptured indirect-detection experiment (EXSIDE) and 1H-15N CIGARAD-HMBC (constant time inverse-detection gradient accordion rescaled heteronuclear multiple bond correlation) were applied for determination of long-range carbon?proton coupling constants nJCH (n = 2, 3, and 4) and for assignment of 15N chemical shift at natural abundance, respectively. DFT/B3LYP optimization studies were performed in order to determine the geometry of 2c using 6-31G(d,p), 6-311G(d,p), and 6?311 + G(d,p) basis sets. For calculation of 1H and 13C chemical shifts, nJHH (n = 2, 3, 4, 5, and 6), and nJCH (n = 1, 2, 3, and 4) coupling constants, the GIAO method was employed at the B3LYP/6-31G(d,p), B3LYP/6-31+G(d,p), B3LYP/6-311+G(d,p), B3LYP/6-311++G(2d,2p), B3LYP/cc-pVTZ), and B3LYP/aug-cc-pVTZ) levels of theory. For the first time, a stereochemical dependence magnitude of the long-range nJHH (n = 4, 5, and 6) and nJCH (n = 1, 2, 3, 4, and 5) have been found in bromo-substituted analogues of Tröger´s bases.