Facile Synthesis Of3-Aryl-1,2,4-benzotriazines Using AllylSmBr/HMPA And Study On The Oxina-Cope Rearrangement To Synthesize Chiral2-ene-1,5-diols

In the first part of the thesis, a novel single-electron transfer (SET) agent of allylSmBr/HMPA was developed for the facile synthesis of3-aryl-1,2,4-benzotriazines.1,2,4-Triazines are popular heterocyclic compounds and some of them are reported to possess important biological activities. Although a number of synthetic methods were available, most of them suffer from their own limitations. We reported that3-aryl-1,2,4-benzotriazines could be constructed via a ring-expansion of1,1-bis(benzotriazol-1-yl)methylarenes in the presence of allylSmBr. However, the low yield retards its application as a synthetic method. To address this problem, this thesis further probes the property of allylSmBr, traditionally used as a nucleophile, especially with HMPA as an additive. As a fortunate, the isolated yields of3-aryI-1,2,4-benzotriazines were improved up to77%. The radical process was proposed based on the preliminary mechanistic studies. The propensity of allylSmBr/HMPA was also investigated on other reductive coupling reactions. These explorations encourage the development of allylSmBr-additive as an efficient SET reagent in organic synthesis.In the second part, the development of oxina-Cope rearrangement to synthesize chiral2-ene-1,5-diols is discussed. Chiral1,5-diols are widely found in many biologically significant natural products, and utilized as important synthetic intermediates. The exiting method to synthesize the chiral1,5-diol moiety mainly relies on multiple steps synthesis. The recent double allylation approach offers a efficient way to furnish this key intermediate. However, the moderate stereoselectivity on some substances and expensive chiral borane reagent limited its application in organic synthesis. The importance of chiral2-ene-1,5-diols and synthetic challenge lead us to devise two strategies from readily available a-allenic alcohol:Firstly, a stereoselective hydrostannation of allene alcohol and subsequent allylation of aldehyde to deliver2-ene-1,5-diols; Secondly, using hydroboration, allylation, and oxina-Cope rearrangement as key transformations,1,5-diols can be established with a high stereoselectivity. The model substrate gave a excellent stereochemistry control and clearly would promote its application on other substances in the context of the concise synthesis of complex natural products. The research on this line is currently pursued in this laboratory.