Ring Opening And Ring Expansion Reactions Of Aziridines Based On Aziridinum Ions

Aziridines and their derivatives are not only abundantly present in biologically active natural products and synthetic drugs,but also play an extremely important role as synthetic intermediates,ligands,chiral transfer agents.The ring tension of aziridines is the basis of their reaction diversity,and a series of reactions such as ring opening,ring expansion,and ring formation greatly enrich the application of aziridines.Aziridines can be classified into activated and non-activated aziridines depending on the substituent on their nitrogen atom.In this dissertation,the optically active aziridine-containing tridentate imine ligands,2-alkylidene-1,3-oxazolidine derivatives,and N-alkenyl-?-carbonyl amide derivatives were synthesized from non-activated aziridines.The reaction of the analogue thiiranes with a-diazo-?-1,3-dicarbonyl compounds under metal catalysis was also investigated.Firstly,an efficient method for the direct synthesis of aziridine-containing chiral tridentate imine ligands was developed from enantiopure aziridines and salicylaldehydes.This method achieved the regiospecific cleavage of more substituted C-N bonds of aziridines through the iminium-mediated self-ring opening reaction of aziridines and complete inversion of configuration with up to 95%yield.The limitation of the instability of the imine products was overcome due to the presence of intramolecular hydrogen bonds.The(S)-2-alkylaziridine-derived tridentate imine ligands displayed exceptionally high activity and stereoselectivity in the asymmetric aldol reactions of aromatic aldehydes with acetone(up to 98%yield and 94%ee).In addition,the reaction of o-mercaptobenzaldehyde with aziridines was also tried,and the benzo[f][1,4]thiazepine containing an imine structure was successfully obtained.Secondly,the preparation of 2-alkylidene-1,3-oxazolidine derivatives were successfully carried out using N-unprotected aziridines and diazo 1,3-dicarbonyl compounds as raw materials.Oxazolidine derivatives are very important heterocyclic compounds which are widely present in many biologically active drugs and natural products.The reaction used microwave-assisted heating,which could quickly and easily convert a-diazo-?-1,3-dicarbonyl compounds into a-carbonyl ketene intermediates by the Wolff rearrangement reaction without metal catalyst.Aziridines underwent nucleophilic addition-cyclization tandem reaction with the ketene intermediates to form five-membered 1,3-oxazolidine heterocyclic compounds.2-Alkylidene-1,3-oxazolidines were first obtained by[3+2]annulation reaction of the C=O double bond of ketenes with aziridines.Further,N-alkenyl-?-carbonylamide derivatives were synthesized from N-alkyl-2,2-disubstituted aziridines and diazo 1,3-dicarbonyl compounds.This reaction could be achieved under two different reaction conditions:first,N-alkenyl-?-carbonylamides could be obtained with isolated yields of up to 98%through ordinary reflux.However,the limitation of this method was that only a-diazo-?-1,3-diaryl-1,3-diketone compounds could be obtained with high yields,and this method did not work well for other types of diazo compounds(Such as cyclic or alkyl-substituted a-diazo-1,3-diketone compounds and diazo ?-carbonyl carboxylates).Second,the synthesis of N-alkenyl-?-carbonylamide compounds was achieved in excellent yields by microwave-assisted heating.The method was simple and efficient for various types of diazo 1,3-dicarbonyl compounds,and the yields were almost over 90%(up to 99%).The N-alkenyl-?-carbonylamide compounds could be further used to synthesize ?-lactam compounds.Mechanistic studies had shown that the reaction for forming N-alkenyl-?-carbonylamides underwent an El elimination mechanism.Finally,synthesis of 3-acyl-5,6-dihydro-1,4-oxathiins has been achieved by reaction of a-diazo-?-1,3-dicarbonyl compounds and thiiranes under microwave and copper sulfate-assisted conditions.The current method provides a new and simple strategy in efficient preparation of 1,4-oxathiins from readily available thiiranes,and trans-3-acyl-5,6-dihydro-1,4-oxathiins as stereospecific products for 1,2-disubstituted cis-thiiranes.3-Acyl-1,4-oxathiins have unique applications in agrochemical and pharmaceutical chemistry.