Construction Of Pyrazolines With A Quaternary Carbon Center Via Cycloaddition Of Diazoesters To 9-allenyl Purines

Pyrazolines with a quaternary carbon center are prevalent in many biologically active molecules.Representative examples for such pyrazolines are shown.Mefenpyr-diethyl is a herbicide safener with favorable toxicological,ecotoxicological and environmental behavior.RH 3421 is an insecticide,which could block both peripheral and central neuronal activities in insects.Therefore,an efficient method to construct pyrazolines bearing a quaternary carbon center is highly desirable.The 1,3-dipolar cycloaddition of diazo compounds with olefinic dipolarophiles represents an efficient approach for the synthesis of pyrazoline derivatives.During the past few decades,alkenes or alkynes have been extensively investigated and well-developed in the cycloaddition with diazo compounds.In sharp contrast,allenes have been less studied as partners in such cycloaddition with diazo compounds,presumably due to the difficulty in controlling the regioselectivity of the two adjacent C=C double bonds in allenes.To the best of our knowledge,there is hardly of 1,3-dipolar cycloaddition between?-alkyl/aryl diazoesters and allenes has been reported up to date.In the context of our ongoing studies on modifying purines and nucleosides,herein,we report the regioselective 1,3-dipolar cycloaddition between N-heteroaromatic substituted allenes and?-alkyl/aryl diazoesters,affording diverse pyrazoline derivatives with a quaternary carbon center in moderate to high yields.In this study,we have introduced the study on the regioselectivity of 9-allenyl purine and?-alkyl/aryl diazoesters,and obtained the poly functionalized purine analogues of different pyrazolines.Furthermore,we synthesized purine compounds with pyrazoline skeleton by using DPPB or Pd₂?dba?₃to catalyze 9-allenyl purine and?-diazoesters.By changing the catalyst,we can control the regioselectivity of the reaction.And the E/Z formula of the product is also controlled.In the examination of the universality of the substrate,we modified and reformed the functional groups on the purine.And synthesized a series of nucleoside analogues with the structure of the allenes.Meanwhile,we synthesized alkyl and aryl substituted diazoesters substrates and enriched the type of substituents on pyrazoline ring.Finally,we further derivatized the two reacted pyrazoline products.And we modified the structure of the substituent functional group of pyrazoline with the enrichment of the species of the products.The newly synthesized compounds that have not been identified in the previous reports have been characterized by ¹H NMR,¹³C NMR,HRMS and so on.All these characterization shows the results are correct.The single crystal diffraction technique was used to characterize the structure of the derivatives,and the configuration of all the products in the template reaction was obtained by other characterization methods.