K. Hintzer

Evaluation of nickel(II) bis[α-(heptafluorobutanoyl)-terpeneketonates] as chiral stationary phases for the enantiomer separation of alkyl-substituted cyclic ethers by complexation gas chromatography

Abstract A method is described which permits the determination of thermodynamic data for molecular association, as well as the enantioselectivity — Δ R,S (Δ G °), from relative retention data by complexation gas chromatography. Thus, the solute—solvent association equilibria between two achiral, and fifteen chiral alkyl-substituted cyclic ethers and twelve non-racemic nickel(II) bis[α-(heptafluorobutanoyl)terpeneketonates] in squalane have been measured at 60°C. The selectivity of the solute—solvent association between alkyl-substituted oxiranes and the twelve nickel terpeneketonates follows a common trend which is rationalized in terms of opposing electronic and steric effects of the Lewis bases. The origin of the striking influence of ring size of cyclic ethers on the association strength with the twelve nickel terpeneketonates, which varies by two orders of magnitude, is unknown. Improved chiral stationary phases for the enantiomer separation of alkyl-substituted cyclic ethers have been found. The highest enantiomeric bias on racemic oxiranes is induced by nickel(II) bis[3-(hepta-fluorobutanoyl)-(1 R ,2 S )-pinan-4-onate], containing a bicyclic terpene structure, and by nickel(II) bis[5-(heptafluorobutanoyl)-( S )-carvonate], containing a monocyclic terpene structure, respectively. The enantioselectivity, — Δ R,S (Δ G °), is generally high when the solute—solvent interaction is intermediate. For chiral alkyl-substituted oxiranes a consistent relationship between molecular configuration and the order of elution is observed for almost all of the twelve nickel terpeneketonates used as solvent. The synthesis of these solvents is described in detail.

Synthesis of optically active 2s-, and 7s-methyl-1.6-dioxa-spiro[4.5] decane, the pheromone components of Paravespula vulgaris (L.), from S-ethyl lactate.

Abstract (−)-2S, 5RS- 1 and (−]-7S, 5S- 2 are obtained from S-ethyl lactate 4 and their absolute configuration is thus directly correlated. Accurate enantiomeric compositions of intermediates and products were measured by complexation gas chromatography on nickel-, and manganese- bis -3-heptafluorobutyryl-1R-camphorate, 3 . It could be conclusively established that the syntheses proceed with a high degree of preservation of configuration.

Enantioselective epoxidation of unfunctionalized simple olefins by non-racemic molybdenum(VI)(oxo-diperoxo) complexes

Abstract Molybdenum(VI)(oxo-diperoxo) complexes bearing bidentate ligands with hydroxy and carbonyl functions show asymmetric induction in the stoichiometric epoxidation of simple prochiral olefins. The influence of the ligand and alkene structure on the enantiomeric excess of the oxiranes has been investigated. The addition of chiral diols to the molybdenum(VI)(oxo-diperoxo) reagents gives high enantiomeric excesses probably because of an efficient kinetic resolution of the oxiranes formed.

Enantioselective synthesis of 3-demethoxyaranciamycinone via asymmetric epoxidation

Abstract The tetracyclic olefin 1 was enantioselectively epoxidized using a molybdenum(VI)- oxodiperoxo complex containing a chiral lactamide. Conversion to the glycosides 8 and 9 showed the epoxide 2 to be the predominant (3 : 1) enantiomer.

Enantiomer resolution of spiroketals

Indigo was thought to exist in only one solid form, while thioindigo and selenoindigo are known in several crystalline modifications [1]. The new modification of indigo, now called indigo B, was discovered coexisting with the known form, indigo A, among crystals grown from vapor at 10 Torr. Under these conditions approximately 90% of the crystals were found to be indigo A and 10% to be indigo B.

Chirality rule for substituted oxiranes

The molecular dichroism sign of the 3s Rydberg transition of oxiranes is correlated with the absolute configuration of the molecule.