K5[PW11ZnO39].23H2O-catalyzed acylation/ring expansion of ketoaziridines in a single pot: a new regio- and stereo-selective route for the synthesis of oxazolines

Abstract

and synthesis of the derivatives of serines as a antibiotics [13] synthesis of N-hydroxy-N-amino acids [14] and as starting material in the synthesis of the neurotrophic factor Lactacystin [15,16]. Moreover, various oxazolines with biological activity have been isolated from marine organisms [17,18].For many years, several synthetic methods have been described for the synthesis of oxazolines [19][20][21][22]. On the other hand, Aziridines are also well known as useful reagents for the synthesis of many categories of nitrogencontaining compounds, in particular N-heterocycles compounds such as oxazolines, thiazolidinones, thiazolidine thiones, and imidazolidinones [23].Among the synthetic applications of these compounds, the rearrangement of N-activated aziridines has become the object of attention only very recently [24]. Acyl aziridines could rearrange to oxazolines through a ring expansion reaction [25][26][27][28][29]. The ring expansion of N-acyl aziridines to oxazolines can be promoted by thermal, acidic, or nucleophilic conditions [30][31][32][33][34][35][36][37][38].However, catalytic examples for the synthesis of oxazolines are rare [39]. Here we report synthesis of N-acyl ketoaziridines from the corresponding ketoaziridines with acyl chlorides. Then N-acyl ketoaziridines in the presence of a nucleophilic and Lewis acids afforded oxazolines [40][41][42].Although a few methods have been described for the preparation of N-acyl aziridines none of them described direct synthesis of oxazolines from N-H aziridines with carboxylic acid .In continuation of our recent interest in the reaction of ketoaziridines [48] and success for using Polyoxometalates [49], herein, we report a one-pot regio-and stereo-selective synthesis of trans-4-benzoyloxazolines, catalyzed by the K 5 [PW 11 ZnO 39 ].23H 2 O catalytic system with moderate to good yields under mild conditions. Abstract A new and one-pot synthesis of oxazolines has been accomplished by K 5 [PW 11 ZnO 39 ].23H 2 O-catalyst acylation followed by C-N ring opening/C-O bond formation in NH ketoaziridines. This regio-and stereo-selective reaction presumably proceeds via a domino sequence resulting in the in situ generation of acyl aziridine which undergoes a ring expansion reaction via an initial C-N rupture of aziridine ring followed by ring closure to the oxazolines. The methodology provided novel one-pot procedure for the synthesis of trans-2,5-diaryl-4-aroyloxazolines.

Recent Advances in the Chemistry of 2-Acylaziridines

“…4-Benzoyloxazolines 78 were also obtained without isolation of 1-acylaziridines starting from NH-aziridines 79 (Scheme 19). 29 Acylation by a reagent generated in situ from PhCOOH and DCC is followed by aziridine ring expansion to oxazoline in the same way as described above. 28 Supposedly, this unordinary catalyst facilitates both reaction steps.…”