Determination of the Absolute Configuration of 1,5-Diaza-cis-decalin by Comparison of Measured and Calculated CD-Spectra

Abstract

The absolute configurations of both 1,5-diaza-c/s-decalin enantiomers were determined by com-parison of measured and calculated CD spectra. CD spectra for both enantiomers were recorded. Theoretical CD spectra for one of the isomers were calculated by means of the semiempirical CNDO/2S method. Eight local minima on the energy hypersurface of the title compound were used to describe the conformer equilibrium mixture. The geometries of these conformers were calculated employing one-determinant ab initio calculations using the split valence 6-31G* basis set. Boltzmann factors were then obtained using relative energies calculated with three different basis sets and including correlation(MP2)-and zero point vibrational energy. Comparing the sign of the observed and calculated longest wavelength Cotton effect, we assign an absolute configuration to the compound. This assignment was verified by means of X-ray structure determination of one of the enantiomers’ α-methoxy-α-trifluoromethylphenyl aceticacid (MTPA, Mosher’s reagent) derivative.

Absolute Configuration in 4-Alkyl- and 4-Aryl-3,4-dihydro-2(1H)-pyrimidones: A Combined Theoretical and Experimental Investigation

“…Ab initio calculations of electronic excitation energies were also done by the single excitation configuration interaction (CIS) procedure (Gaussian 98). CD spectra were simulated 24,[47][48][49] as sums of Gaussians centered at the wavelengths of the corresponding electronic transitions and multiplied by the calculated rotational strength. An empirical half bandwidth of 7 nm at 1/e of the maximum 24,49…”

Synthesis and Resolution of a Novel Chiral Diamine Ligand and Application to Asymmetric Lithiation−Substitution

“…Hoffmann et al have independently shown that similar reaction conditions result in similar improvement (see ref a).…”

“…In the case of the 1,5-diaza- cis -decalins, the position of the equilibrium between the desired conformation capable of bidentate coordination, 11-in , and the other major conformation, 11-out , varies depending upon substituents (R), solvent, and additive. In an elegant study, Hoffmann and co-workers have shown that when the R groups are small, 11-in is favored and when the R groups are large, 11-out becomes favored. Regardless, the two conformations are energetically similar enough that the addition of acid or LiClO 4 shifts the equilibrium toward 11-in .…”

Characteristic Conformation of Mosher’s Amide Elucidated Using the Cambridge Structural Database

“…In this study, all MTPA amides were processed as (Racid)-MTPA amides; that is, the dihedral angles of (Sacid)-MTPA amides cited in Table 1 were substituted by those of the mirror images (i.e., Racid-enantiomers) with plus/minus sign reversal [82]. Each of bis-and tetrakis-MTPA amides (i.e., CCDC 1280861 [55] [61], and CCDC 1294281 [56]), was processed individually. This procedure yielded 58 of (Racid)-MTPA amide moieties.…”

“…The MTPA amide moieties prepared from cyclic secondary amines exhibited the Z forms (i.e., CCDC 140352 [38] [54], and the two conformers of CCDC 1280861 [55]). …”