Chemo-and Regioselective Ring-Opening Of Donor-Acceptor Oxiranes With N-Heteroaromatics

Donor-Acceptor（D-A）oxiranes are exceptionally useful three-atom building blocks in organic synthesis.Due to the inherent tension of the oxiranes structure,the chemoselectivity of C-C bond and C-O bond cleavage may appear in different coordination modes.Cycloaddition of D-A oxiranes with various unsaturated double bond and triple bond compounds have been elegantly conducted,but the ring-opening of D-A oxiranes is rarely reported.Benzotriazole derivaties and acyclic nucleoside analogues,containing N-glycosidic bonds,have displayed significant bioactivities.Therefore,the development of such compounds by ring-opening of D-A oxiranes to N-heteroaromatics is of great significance.In this paper,a Lewis acid catalyzed ring-opening of D-A oxiranes to N-heteroaromatics with a C-C bond cleavage,affording diverse acyclic heteroaromatics containing a N-glycosidic bond was reported.The N-heteroaromatics were benzotriazoles,purines,imidazole and pyrazole compounds.Due to the existence of two tautomeric forms for benzotriazole and purines,it might face the challenge of regioselectivity.Significantly,with the Y（OTf）₃ as the catalyst,a variety of N-heteroaromatics reacted well with diverse D-A oxiranes,providing ring-opening adducts containing a N-glycosidic bond in up to 97%yield and up to>95:5 regioselectivity.Ganciclovir analogues could be afforded from the ring-opening products through reduction.The path of the ring-opening reaction was explored through mechanism experiments.The struture of the products were determined by X-ray diffraction analysis.Finally,asymmetric catalysis was investigated for this reaction.After a series of screening of catalyst and reaction conditions,no satisfactory experimental results were obtained,and the work was continuing.We report a ring-opening of D-A oxiranes to N-heteroaromatics,affording diverse acyclic nucleoside analogues containing a N-glycosidic bond in a highly chemo-and regioselective manner,which could be derived into Ganciclovir analogues.All the new compounds obtained were characterized by ~1H NMR,¹³C NMR,HRMS,and IR.