Alfons L. Baumstark

Epoxidation of alkenes by dimethyldioxirane: Evidence for a spiro transition state

The relative reactivity series for the epoxidation of alkenes by dimethyldioxirane showed the reaction to be unexpectedly sensitive to steric factors; cis compounds were ∼8 times as reactive as the trans isomers.

Dimethyldioxirane: mechanism of benzaldehyde oxidation

Abstract Under inert atmosphere, dimethyldioxirane 1 converts benzaldehydes solely to the corresponding acids; the reaction is insensitive to electronic effects; yields are limited by the competing decomposition of 1 to acetol; O2 trapping of free-radical intermediates is observed.

Oxygen-atom transfer reagents: new, reactive α-azohydroperoxides

Abstract 3,4,4-Trimethyl-4,5-dihydro-5-hydroperoxy-3,5-diaryl-3H-pyrazoles, synthesized by autoxidation of the corresponding 3,4-dihydro-2H-pyrazoles, are a new type of cyclic α-azohydroperoxide which is of high reactivity in oxygen-atom transfer chemistry.

17O NMR spectroscopy: unusual substituent effects in para-substituted benzyl alcohols and acetates

Abstract The 17 O chemical shifts for para -substituted benzyl alcohols and acetates were measured: electron donating substituents resulted in deshielding and electron withdrawing groups resulted in shielding of the chemical shift; the data are correlated by DSP treatment.

Oxidation of α-methylbenzyl alcohols by dimethyldioxirane

Abstract Dimethyldioxirane converts p -substituted α-methylbenzyl alcohols to the corresponding acetophenones in excellent yield with α-hydroxyacetophenones as the minor products; the oxidation shows a ϱ of −1.57, PKIE of 3.55, KIE of 1.09 for OD and activation parameters with a large, negative ΔS ‡ term.

17O NMR spectroscopy: Origin of deshielding effects in rigid, planar molecules

Abstract 17 O NMR data for hindered carbonyls in planar quinones and flavones showed large deshielding effects and correlated with estimated repulsive van der Waals interactions, providing new insights into steric phenomenon at carbonyl oxygens.

Reaction of tetramethyl-1,2-dioxetane with phosphines: deuterium isotope effects

Avec les phosphines tertiaires, il y a formation de tetramethyl-4,4,5,5 dioxaphospholannes-1,3,2 trisubstitues en 2,2,2 par insertion concertee de la phosphine dans la liaison peroxy du dioxetanne

17O-enriched α-azohydroperoxides: 17O NMR spectroscopy, 17O-labeling reagents

Abstract 17 O-enriched α-azohydroperoxides, prepared by autoxidation, are efficient 17 O-labeling reagents; 17 O NMR (CD 3 CN) of 2 showed broad signals at δ 254 and 204 PPM; the solvent dependence of the 17 O chemical shifts and the kinetics of ionic oxidations are interrelated.

Oxidation of amines and sulfides by 3-bromo-4,5-dihydro-5-hydroperoxy-4,4-dimethyl-3,5-diphenyl-3h-pyrazole

The reaction of 3-bromo-4,5-dihydro-5-hydroperoxy-4,4-dimethyl-3,5-diphenyl-3H-pyrazole with tertiary amines and sulfides produced amine oxides and sulfoxides in high yield with k2s for amines similar to those reported for reaction of amines with a 4a-hydroperoxyflavin.

17O NMR spectroscopic study of steric hindrance in phthalic anhydrides and phthalides

Abstract 17 O NMR data for sterically hindered phthalic anhydrides and phthalides showed unusual deshielding effects which were correlated with in-plane bond angle distortions (X-ray results and MM2 calculations); indicative of van der Waals repulsions.