A New Method for the Construction of Macrolides Stereoselective Synthesis of (±)-Phoracantholide J. Preliminary communication

Starting from 5-chloro-2-pentanone ( 1 ) the naturally occurring 10-membered lactone phoracantholide J ( 8a ) has been synthesized as its racemate in a sequence of six steps (Scheme 2). Salient features of the syntheis include an internal selenium assisted acetal formation ( 4→5 ) and a stereoselective Claisen rearrangement ( 6→7→8 ). This general synthetic strategy offers an alternative approach towards the construction of macrocyclic lactones.     

Studies in mass spectrometry. IV—Fragmentation of aryltriflates. Substituent effects on [ArO]+ ion abundances: Looking for a best suited electron energy in the steady state approach. Experimental evidence for the ‘through bond’ stabilization of aryl cations by meta electron donor Substituents

The fragmentation patterns of 24 substituted phenyltrifluoromethanesulfonates has been determined by exact mass and metastable transition measurements. The influence of the ring substituent(s) on the abundance of the [ArO]+ ions has been investigated at low energies and a new standard parameter for plotting against Hammett's ó constants is proposed. The direct loss of CF₃SO₃ from the molecular ion of 3,5-(diisopropyl)-phenyl-, 3,5-(dicyclopropyl)phenyl- and 3,5-di(α-methylcyclopropyl)-phenyl-methanesulfonate, and further observations on the fragmentation processes of these compounds are consistent with M.O. calculations on the ‘through bond’ stabilization of the [Ar]+ σ state by meta electron donor substituents.     

Structural Aspects of the Enantioselectivity of Tartrates with α-Amino-alcohol Salts. Part II. Crystal structures of (1R, 2S)-norephedrine hydrochloride and (1R, 2R)- norpseudoephedrine hydrochloride

Enantioselective host-guest complexes between α-amino-alcohol salts and chiral tartrates can not be crystallised up to now. To study structural aspects of their enantioselectivity, crystal structures of the components were determined. Norephedrine was used as a reference guest α-amino-alcohol. (1R, 2S)-Norephedrine hydrochloride (monoclinic, space group P2₁ Z = 4, a = 8.455, b = 10.331, c = 12.570 Å, β = 107.45°) and (1R, 2R)-norpseudoephedrine hydrochloride (monoclinic, space group P2₁ Z = 2, a = 5.493, b = 8.052, c = 11.986 Å, β = 104.62°) both adopt M-synclinal conformations with respect to the ammonium and hydroxy groups. Rather short intramolecular N…?O distances indicate interaction between ammonium and hydroxy groups.     

A Highly Stereoselective Synthesis of C(11)-Functionalized Aromatic Steroids by an Intramolecular Benzocyclobutene-Olefin -Cycloaddition. Preliminary Communication

The racemic cis-anti-trans-steroids 9 to 11 have been synthesized in a highly stereoselective manner starting from 4-methoxybenzocyclobutene carboxylic acid via the key step 8 → 9 . (cf. Scheme 2).     

Nonlinear intensity dependence of the rate coefficient in unimolecular reactions induced by monochromatic infrared radiation

It is shown that essentially incoherent, stepwise one-photon transitions arising in dense multilevel structures of polyatomic molecules irradiated with monochromatic coherent infrared radiation can give rise (under specified conditions) to a more than proportional intensity dependence of the steady-state rate coefficient in unimolecular reactions induced by monochromatic infrared radiation.     

13C-NMR studies of marine natural products II. Total assignment of the 13C-NMR spectrum of asperdiol

¹³C-nmr spectral assignments for asperdiol are made with the aid of model compounds and T₁ relaxation behavior. Overall isotropic tumbling was inferred from the latter providing a supplemental means of multiplicity determination. Utilization of the T₁ relaxation times as an assignment criterion for select resonances in asperdiol is also described.     

Borel fibrations and G-spaces

Considering discrete groups G only, we present an elementary proof of the familiar equivalence of the category of G-spaces (with maps equivariant up to homotopy) and the category of Borel fibrations over BG.     

Dynamical systems with relaxation time

We define mathematically a class of dynamical systems that exhibit relaxation corresponding to that observed in physical systems, and then show that this class is identical with the class ofK-mixing dynamical systems.