Inherently Dissymmetric Chromophores and Circular Dichroism. II

Determination of absolute configurations and conformations of organic compounds by theoretical calculations of CD spectra

“…We used this technique, notably with microcrystalline triacetylcellulose (TAC), [33][34][35] to resolve All four forms could be separated by chromatography on TAC, and crystal structure determinations of the pure (+)-e,e and (−)-a,a enantiomers showed that the (+) form with positive A band in the CD spectrum has the R configuration and the (−) form with negative A band ( Fig. 2) has the S configuration, thus confirming the assignment by Mislow et al [29][30][31] According to the crystallographic study and force-field calculations, both conformers have dihedral angles of ca. 60°(⍜) between the phenyl rings.…”

“…28 Bridges of more than one atom give rise to chiral biphenyls, although systems with two-and three-carbon bridges are found to undergo rapid racemization at ambient temperature unless the bridge contains one or more chiral centra. Mislow and co-workers [29][30][31] early showed that chiral bridged biphenyls without polar substituents and R configuration display a positive A band in the CD spectrum (a positive Cotton effect in the ORD spectrum).…”

Dibenzocycloheptanoids from the Leaves of Cinnamomum subavenium

“…The known compounds, whose cited references and structures are shown in the Supporting Information, are gibberodione (9), dihydrodehydrodiconiferyl alcohol β-D-xylopyranoside (10), 3-hexenyl β-D-glucopyranoside (11), chavicol 4-O-β-D-apiofuranosyl-(1→6)-β-D-glucopyranoside (12), 1-butyrylphloroglucinol β-D-glucopyranoside (13), hydroxytyrosol (14), nine flavonoids, catechin (15), epicatechin (16), phloridzin (17), (2R)-naringenin 5-O-β-D-glucopyranoside (18), (2S)-naringenin 5-O-β-D-glucopyranoside (19), 7-O-β-D-glucopyranoside (20), kaempferol 3-O-β-D-glucopyranoside (21), 3-O-α-L-rhamnopyranoside (22), and 3-O-α-L-rhamnopyranosyl-(1→6)-β-D-glucopyranoside (23), and two tannins, cinnamtannins B-1 (24) and D-1 (25). Compounds 1, 3, 4, 6, and 7 are 3,9,10-trioxygenated 7-oxymethyl-5H-dibenzo[a,c]cycloheptatrienes, as evidenced by their 1 H NMR spectra (600 MHz), all displaying an ABX (1: δ 6.78, d, H-4; 6.81, dd, H-2; 7.34, d, H-1; J 2,4 = 2.5 Hz, J 1,2 = 8.5 Hz) or AMX system (3,4,6,7) and two singlets (1: δ 7.03 and 7.18) in the aromatic region and a broad triplet for an olefinic proton (1: δ 6.12, J = 7.2 Hz, H-6) ( Table 1).…”

Novel atropisomeric aminophosphine ligands with a bridge across the 5,5′-position of biphenyl for Rh(I)-catalyzed asymmetric hydrogenation

“…This signed feature is the characteristic of (R)-configuration at chiral axis, which was in contrast with the spectra in the literature of axially chiral biphenyl compounds. 20 To evaluate the effectiveness of our atropisomeric bisaminophophine ligands 2 in Rh(I)-catalyzed asymmetric hydrogenation, typically, (Z)-a-acetamidocinnamic acid (8) was used as a model substrate for the hydrogenation. The hydrogenation reaction was catalyzed by 1 mol % of the Rh(I)-(R)-2a complex generated in situ by mixing Rh(COD) 2 BF 4 with bisaminophosphine (R)-2a in methanol at room temperature.…”