Study On The Synthesis Of Hetero-helicene-likes And Heterocyclic Compounds Induced By Low-valent Titanium Reagent

Low-valent titanium reagent is one of the new key organic synthesis reagents, which has been widely used in inter-and intra-molecular reductive coupling reactions. Our interest is to investigate reductive coupling reactions induced by low-valent titanium reagent. This dissertation consisted of two parts. The first one is focused on the synthesis of hetero-helicene-likes induced by low-valent titanium reagent. The second is the synthesis of heterocyclic compounds induced by low-valent titanium reagent.In part one,2-hydroxybenzaldehydes (or 2-nitrobenzaldehydes) and diamines were utilized as the starting materials, the formed diimines then undergo a reductive-cyclization process with triphosgene to give the nitogen, oxygen-containg helicene skeleton induced by low-valent titanium reagent. [5] and [7] helicene-like compounds have been synthesized by modifying the structure of aldehydes, and the structures of the products have been determined by the X-ray crystallographic analysis. In addition, when 1,2-diaminoethanes act as the substrates, the final products were found to be in the trans-isomer, while the propane-1,3-diamines gave the related products in syn-isomer, as a result, hetero-helicene-likes in different geometry could be synthesized by altering the diamine.The second one is focused on the synthesis of heterocyclic compounds induced by low-valent titanium reagent.In section three, a one-pot multicomponent reaction involving 1,3-dicarbonyl compounds, aldehydes and amines induced by low-valent titanium reagent, which gave new series of 1,2,3,5-tetrasubstituted pyrroles as well as hydroindoles have been disclosed. The reaction went smoothly and gave the target products in the yield of 75%-98% in 15 min. Moreover, for the unsymmetric 1,3-dicarbonyl compounds, only one kind of products were isolated, which provided an convenient and efficient protocol for the synthesis of polysubstituted pyrroles. This new method has the advantages of high regioselectivity.In the forth chapter, a facile reductive coupling reaction of nitro-compounds with isothiocyanates or isocyanates promoted by low-valent titanium reagent were studied: an access to 2-thioxoquinazolinone, quinazolin-2,4-dione, imidazo[1,2-c] quinazolin-5-amine and benzimidazo[1,2-c]quinazolin-5-amine derivatives.In the fifth chapter, a mild, efficient, one-pot protocol for the synthesis of indazole-3(2H)-ones via cyclization of nitro-aryl substrates through low-valent titanium reagent has been described. The method used triethylamine(TEA) to control pH. Particularly,2-aminobenzonitriles were synthesized by one step easily. The mechanistic course of the reaction suggests the involvement of an anion leading to an intramolecular cyclization via N-N bond formation.In the sixth chapter, the synthesis of a series of biquinazoline-2,2'-diones starting from o-nitrobenzaldehydes, anilines and triphosgene is presented. This general approach features a novel and easy way for access to the target products. The mechanistic course of the reaction suggests the involvement of reduction, coupling and cyclization by one-pot. These compounds were also investigated in vitro for anticancer activity, and some were found to have good anticancer activity.In the seventh chapter, symmetrical and unsymmetric bibenzo[e][1,3]oxazine-2,2'-diones were first synthesized in satisfactory to good yields via the reaction of triphosgene and various o-hydroxy Schiff base with the aid of low-valent titanium reagent. Possible mechanism as well as optimization and reaction scope studies are reported.The remarkable advantages of the above mentioned reactions are mild, neutral, simple operation, good yields and high selectivity.