Studies On The Synthesis And Rearrangement Properties Of N-vinyl Nitrones

N-vinyl nitrones,due to the rich chemistry of the double bond,are versatile and important types of compounds and can undergo a variety of reactions.Recently,N-vinyl nitrones have attracted much attentions as useful synthetic intermediates and showed distinctive characteristics,which can provide a new way to prepare alkaloid derivatives,and products with biological,pharmaceutical and other activities.Therefore,the research on the synthesis and application of N-vinyl nitrones is desirable.This thesis mainly focused on copper-catalyzed selective N-vinylation of3-(hydroxyimino)indolin-2-ones with alkenyl boronic acids to synthesis of N-vinyl nitrones and spirooxindoles,We further developed an iron(III)-catalyzed selective N-O bond cleavage to prepare tetrasubstituted pyridines and 3,5-disubstituted isoxazolines from N-vinyl-?,?-unsaturated ketonitrones.This thesis was divided into the following three parts:In the first part,we developed a copper-catalyzed N-vinylation of3-(hydroxyimino)indolin-2-ones with alkenyl boronic acids to prepare(E)-N-vinyl oxindole nitrones.The effects of different copper salts,solvents,bases,and temperatures on the reaction were screened.The reaction tolerated linear and cyclic alkenyl boronic acids with various functional groups in good to excellent yields.The N-vinyl nitrones could undergo a thermal rearrangement to access various spirooxindoles in good yields and high diastereoselectivity.This coupling strategy provided not only a facile method to prepare N-vinyl nitrones but also a good entry for spirooxindoles to be further studied in pharmaceuticals.In the second part,we studied an iron(III)catalyst-controlled cyclization and selective N-O bond cleavage of N-vinyl-?,?-unsaturated nitrones to access tetrasubstituted pyridines in moderate to good yields.The strategy features simple and mild reaction conditions,cheap catalyst-controlled N-O bond cleavage,broad substrate scope and versatility of N-heterocycles.the regioselectivity of cyclization for the formation of pyridines was favorable for styrenyl group with an electron-donating group in nitrone.In the third part,we investigated the iron(III)with ligands controlled cyclization and selective N-O bond cleavage of N-vinyl-?,?-unsaturated nitrones to access3,5-disubstituted isoxazolines in good to excellent yields.The reaction tolerated various N-vinyl-?,?-unsaturated nitrones with functional groups.a new bidentate N-ligand was easily prepared from isoxazoline in 37% yield over four steps and an epoxypyridine scaffold was obtained by using copper acetate combined with the prepared N-ligand.