The P-DDA Reaction Of2-(2-benzoxazolyl)-1-(2-naphthyl)Acetylenes And The Cross P-DDA Between Heteroarylacetylene And Heteroarylethylene

In this paper, Eight unreported2-(2-benzoxazolyl)-1-(2-naphthyl)ethylenes derivatives were synthesized from the reaction of2-methyl-5-R-benzoxazole (R=H, CH3, Cl, t-Bu),2-methylbenzothiazole and2-naphthaldehyde,2-or4-quinolinecarboxaldehyde,1-pyrene aldehyde. Seven unreported2-(2-benzoxazolyl)-1-(2-naphthyl)acetylenes derivatives,1-(2-naphthyl)-2-(5-R-2-benzoxazolyl) acetylene (R=H, CH3, Cl, t-Bu),2-(2-benzothiazolyl)-1-(2-naphthyl)acetylene,2-(2-benzoxazolyl)-1-(2-or4-quinolyl)acetylene were successfully synthesized from the corresponding N-heteroarylethenes by bromination with Br2and then debromination with alkali in tetrahydrofuran.The self-photo-dehydro Diels-Alder (P-DDA) reaction of the2-(2-benzoxazolyl)-1-(2-naphthyl)acetylenes derivatives were carried out in acetonitrile under the irradiation of300W Medium-Pressure Mercury Lamp. Four unreported photodimers,2,3-bis(2-benzoxazolyl)-1-(2-naphthyl)anthracene derivatives were isolated and fully characterized. The mechanism of such P-DDA reaction in CH3CN was discussed.Three kinds of1-(4-R-phenyl)-2-(4-pyridyl)acetylenes (R=H, Cl, Br) derivatives and three kinds of2-(2-benzoxazolyl)-1-(4-R-phenyl) acetylenes (R=H, Cl, Br) derivatives were also synthesized by the same classical bromination and debromination method.The cross P-DDA reaction between heteroarylacetylenes and heteroarylethylenes were also carried out in an acidic aqueous solution with the irradiation of Medium-Pressure Mercury Lamp. It was found that this cross P-DDA reaction is complicated with more by-products. Only three cross P-DDA photodimers with the structure of1-(2-benzoxazolyl)-2-phenyl-3-(4-pyridyl)naphthalene,1-(2-benzothiazolyl)-2-phenyl-3-(4-pyridyl)naphthalene and1-(2-benzothiazolyl)-3-(2-benzoxazolyl)-2-phenylnaphthalene were isolated.The scope of P-DDA reactions was extended in this dissertation to the cross P-DDA reaction between heteroarylacetylenes and heteroarylethylenes. We found the cross P-DDA reaction could only occur in acidic aqueous solution, it was failed when carried out in organic solvent. We also found that carring out the P-DDA reaction under nitrogen can reduce the side reaction and improve the reaction yield. We think that the photodimers of2-(2-benzoxazolyl)-1-(2-naphthyl)acetylenes have a head-to-head structure just like the P-DDA reaction of2-(2-benzoxazolyl)-1-(1-naphthyl)acetylenes.Overall, We have synthesized15N-heteroarylethylenes,13N-heteroarylethylenes and7unreported self and cross P-DDA photodimers. The structures of all the new compounds were fully characterized by IR、1HNMR.13C NMR and HRMS(ESI).