No abstract

Allylpalladium complexes with chiral bis(dihydrooxazole) ligands were studied as catalysts for the enantioselective allylic substitution reaction of rac‐1,3‐diphenylprop‐2‐enyl acetate (rac‐5) with the anion of dimethyl malonate (Scheme 1). Using enantiomerically pure (S,E)‐1‐(4‐tolyl)‐3‐phenylprop‐2‐enyl acatete ((S)‐25) as substrate, the reaction was shown to proceed by a clean ‘syn’ displacement of acetate by dimethyl malonate (Scheme 6). The [Pd11(η3‐allyl)] complex 18 and the analogous [Pd(η3‐1,3‐diphenylallyl)] complex 20, both containing the same bis(dihydrooxazole) ligand, were characterized by X‐ray structure analysis and by NMR spectroscopy in solution. The structural data reveal that steric interactions of the allyl system with the chiral ligand result in selective electronic activation of one of the allylic termini. The higher reactivity of one allylic terminus toward nucleophilic attack is reflected in a significantly longer PdC bond and a shift of the corresponding 13C‐NMR resonance to higher frequency.

No abstract

Although not endogenous in nature, the sulfonamide functionality is widely found in organic molecules with biological activity. A search of Thomson Reuters Integrity reveals that the sulfonamide motif appears in 111 approved drugs or agents in clinical trials, [1] and the total number of organic molecules containing this functional group is enormous. In contrast, the sulfonamide isostere [2] in which one of the sulfonamide oxygen atoms have been replaced by a nitrogen atom, thus creating a sulfonimidamide has received little attention in the literature. The first reports on sulfonimidamides were published in the early 1960s, [3] however, it was only during the last few years that the research groups of Malacria [4] and Dodd [5] explored the use of sulfonimidamides as reagents in organic synthesis, while Bolm et al. explored sulfonimidamides as chiral organocatalysts [6a] and as ligands for transition metal-catalyzed asymmetric synthesis.[6b]

Based on a previously discovered method for amine oxidations using flavins as catalysts and hydrogen peroxide as oxidant, a comparative kinetic study using NMR spectroscopy was undertaken with a series of flavins for amine and thioether oxidations. Included in this series is the newly prepared 7,8-difluoro-1,3-dimethyl-5-ethyl-5,10-dihydroalloxazine. This study shows that flavins, which bear electron-donating groups on the aromatic ring and/or the N-10 position, are less active and are deactivated during the course of the reaction. Moreover, flavins that are alkylated at the N-1 position instead of the N-10 position and having either no substituents or electron-withdrawing groups on the aromatic ring, remain the most active and stable.