Abstract
Interesting properties of N-oxides and pyridine oxazoline compounds have become the starting point to synthesize compounds connecting both groups. A multi-step synthesis of a series of chiral oxazoline substituted pyridine N-oxides, alkyl derived of pyridine N-oxides, bipyridine N-oxides, and isoquinoline N-oxides, based on amino alcohols derived from natural amino acids or other previously prepared, is presented herein. Various synthetic pathways have been designed and tested according to the properties and limitations imposed by the target products. The encountered problems related to the stability of the products were discussed. The resulting compounds (eighteen structures) were tested as catalysts in th e allylation of benzaldehyde (obtaining up to 79% ee) as well as in nitroaldol reaction (obtaining up to 48% ee).
Highlights
Heteroaromatic N-Oxides ModifiedAn increasing interest in the development of the chemistry and applications of Noxides has been observed in the last decade
Dependent on building the azaaromatic framework, two different synthetic routes were successfully applied to obtain a series of novel chiral heteroaromatic N-oxide oxazolines, compounds combining unique properties of N-oxide and oxazoline moieties
The direct procedure for the oxazoline ring closure of N-oxide nitrile with chiral amino alcohol was employed for the synthesis of both 3,5dimethylpyridine- and isoquinoline-substituted-oxazoline N-oxides (10, 20, respectively)
Summary
Heteroaromatic N-Oxides ModifiedAn increasing interest in the development of the chemistry and applications of Noxides has been observed in the last decade. Apart from the fact that azaaromatic N-oxides can be found in nature [1] and their biological activity is recognized, due to their unique properties being a consequence of the N-O moiety presence, they have found various applications. They can serve as oxidants [2], intermediates having significant synthetic value en route to diversely functionalized N-heterocycles, and in industrial syntheses of pharmaceuticals [3]. Heteroaromatic N-oxides are applied as catalysts in both metal-free transformations and metal-catalyzed reactions [6]. As mild Lewis bases with basicity lower than corresponding pyridines, but sufficient enough to catalyze a wide variety of reactions and to activate
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