Chiroptical properties of steroid 1,3-diaxial diols in the presence of [Mo2(OAc)4]

Summary Bidentate complexes of dimolybdenum tetraacetate with 1,3-diaxial diols show Cotton effects around 490–540 nm (CD band I), 400–440 nm (II), 350–380 nm (III), 320 nm (IV) and 280 nm (V). The sign of the Cotton effect II can be predicted by a proposed sector rule. It seems that from the Cotton effects for cyclic 1,3-diols the absolute configurations or conformations can be obtained.A part of this material was presented at III-rd International Conference on CD Spectroscopy [1]     

Circular dichroism—LXVIII compounds from valerian—XII: On the chiroptical properties of valepotriates and related compounds

The CD of saturated iridoids containing a 2.9-dioxatricyclo[4.3.1.03,7] decan skeleton derived from valepotriates is determined by the acetal chromophore. For the less symmetric ring system of 1,6-anhydro hexapyranoses the sign of this CD is predictable. The vicinal effect for enones and diketones in this series is appreciable. A new rule for the correlation between the CD around 190–205 nm of enol ethers and their absolute conformation is given; the same reasoning is applicable to explain the known rules for cisoid and transoid vinyl cyclo-propanes.     

Konformation und Circulardichroismus der Sesquiterpene vom Trichothecan-Typ und deren makrocyclischen Estern

The circular dichroism of keto derivatives with trichothecane skeleton and some of their rearrangement products has been measured. The sign (and sometimes even the magnitude) of all COTTON effects can be explained by applying the respective rules for the cyclohexanone, cyclopentanone, enone and ene-ester chromophores. Thus conformations could also be determined in those cases which did not follow unambiguously from conformational analysis. The conformation of the muconic acid moiety of the macrocyclic ring of verrucarin A is the same in dioxane solution as in the crystalline state.     

Preparation via Diastereoselective Hydrogenation,Absolute Conformation and Configuration of Exogeneous Anabolic Zeranol ((3S, 7R)-3,4,5,6,7,8,9,10,11,12-Decahydro-7,14,16-trihydroxy-3-methy-1H-2-benzoxacyclotetradecin-1-one)

Hydrogenation of the ketone group in di-O-benzylderivative ( 8 ) of the known macrocyclic lactone zeralenone ( 7 ) using a novel chiral borane complex 3 . BH₃, prepared in situ, proceeded at lower temperatures with moderate diastereoselectivity (～40%, d. e. at ?60°). Unsaturated diastereomers 9 and 10 were separated, and 9 converted into zeranol ( 11 ), a known anabolic agent. Restricted conformational mobility at lower temperatures is assumed for the intermediate 8 on the basis of the temperature-dependent CD spectra of its acetyl congeners 18 and 19 . X-Ray structure analysis of 7-O-acetylderivative ( 13 ) of 11 revealed the (R)-configuration at C(7). Two crystallographically independent H₂O molecules are involved in the H-bonds, one of them (O(21)) rises the helices of the molecules of 13 along b. Small positive torsional angle [C(16)-]C(161)-C(1) [=O] (+19.3°), transoid(E) conformation of the lactone group, and nearly achiral arrangement of the C(11)-C(12) bond (torsional angle [C(11)-]C(12)-C(121)[C(161)] is ?93°) are the main conformational features that differentiate the macrocylic RAL (resorcinic-acid lactone) derivatives from the 6-membered lactone derivative 20 , studied earlier by CD. Consequently, the rules developed for the CD effects within conjugation band (around 270 nm), and n→π* band (around 255 nm) of the latter compound, cannot be applied the macrocyclic lactones.     

Circular Dichroism of Some 2-(Phenylmethyl)pyridine Derivatives

The absolute configuration of the 2-(phenylmethyl)pyridine derivatives 1 – 9 had been established by X-ray diffraction and chemical correlation. Their CD spectra have been studied in different solvents for the free and protonated forms. It has now been found that, from the sign of the strong CD couplet between 270 and 220 nm, which was observable for all these compounds besides 7 and 9 , their absolute configuration can be determined much quicker.     

Tetrahydrofurane und Lactone,I. Synthese und Reaktionen chiraler 2,5-überbrückter Tetrahydrofurane – ein neuer Weg zu optisch aktiven γ-Lactonen und γ-Bislactonen

Tetrahydrofurans and Lactones, I. - Synthesis and Reactions of Chiral 2,5-Bridged Tetrahydrofurans - A New Approach to Optically Active γ-Lactones and γ-Bislactones Diels-Alder reaction of 3,4-hexamethylenefuran with acrylic acid gives the carboxylic acid 1a with high endo selectivity. 1a was separated into the enantiomers via the α-phenylethylammonium salts. Comparison of the CD spectra of (−)- 1a and (−)- 3 and the X-ray structural analysis of the camphanoyl derivative (−)- 4b lead to the 1R,2S,4S configuration of (−)- 1a as well. The 2,5-bridged tetrahydrofuran (−)- 5 with all-cis and RSS configuration is obtained by ozonolysis of the ester (−)- 1b . (−)- 5 can be oxidized to the γ-lactone (2R,3S)-(−)- 6 with sodium metaperiodate/potassium permanganate in 22% yield. Hydride reduction of (−)- 6 under various conditions leads to the γ-bislactones (−)- 8 and (−)- 9 or to the bislactol (−)- 10 . (−)- 8 has the same absolute configuration as the naturally occuring (−)-canadensolide.     

Circulardichroismus. XXX

A simple device is described which can be used with the Roussel-Jouan Dichrograph to give direct readings of Δs and Δε/λ, resp. Integration of the latter curve with a planimeter yields the rotatory strength of any partial CD-band.