Preparation, Absolute Configuration and Conformation of Some α-Aryl-2-pyridylmethanols

Abstract

The syntheses of five optically active α-aryl-2-pyridylmethanols 1–5 are described. It is shown by means of chemical correlation with the known (−)-(αR,2S)-α-phenyl-2-piperidylmethanol 6 that all levo-rotatory isomers of 1–4 are of R configuration. It is also found via the relative integral intensities in the infrared spectra of the bands due to free and intramolecularly bonded hydroxyl groups in the compounds 1–4 and the free hydroxyl groups in the model compounds 7–10, that the population of the conformers with an intramolecular OH···N bond in compounds 1–4 exceeds 80%.

Circular Dichroism of Some 2‐(Phenylmethyl)pyridine Derivatives

“…Since we observed a similar CD couplet in unpolar solvents for ent-3 as for 1 and 2, the arrangement of both rings of ent-3 must also be similar to those of 1 and 2. This conclusion from the CD data is supported by the MM-2 calculation [5]. Solvation by MeOH destabilizes this conformation, since in MeOH the CD couplet disappears, and one observes the usual small CD (with fine structure) within the tl band.…”

“…MM-2 calculations for (+)-ent-3 predict [5] that, at room temperature, ca. 80% of the molecules adopt a conformation in which the C(2)-N bond of the pyridine ring is synperiplanar to the C(a)-CH, bond at the bridge.…”

“…CD Spectrum of (+)-6. -In cyclohexane, more than 80 % of (+)-6 are present in a conformation with internal H-bridge [5], arrangement giving rise to a positive C D couplet. Indeed, this is observed, and the same holds even for MeCN, although the magnitudes of the Cotton effects are somewhat smaller than those of ent-7 (see later).…”

“…-The conformation of lowest energy of (+)-ent-7 is, according to calculations, the one in which the Me group is synperiplanar to the pyridine-N-atom [5]. For this, the two transition dipols involved in the exciton interaction lead to a negative CD couplet, which is, indeed, observed for (+)-ent-7 in cyclohexane, MeCN, and even in MeOH solution, although in the last mentioned solvent the couplet is only half as large as for the other two.…”

(6,7-Dimethoxy-4-methylisoquinolinyl)-(4’-methoxyphenyl)-methanone, a New Benzylisoquinoline Alkaloid from Beilschmiedia brevipes

“…The complete 1 H- and 13 C-NMR spectral assignment of ( 2 ) was accomplished by thorough analysis of DEPT, COSY, HMQC, and HMBC data. The absolute configuration at C-α is determined as S due to the positive sign of the specific rotation for alkaloid ( 2 ) = +91° ( c = 0.22, MeOH) [18,19]. …”