Studies On A Few New Reactions Of Hantzsch Ester Known As A Co-enzyme Mimic

On the basis of our group's previous mechanistic investigations on the co-enzyme NADH model compounds, this dissertation was mainly focused on the synthetic methodology based on Hantzsch ester, a NADH model compound. It consists of two parts.A review on the researches about co-enzyme NADH model compounds was given in the first part of this thesis. In the second part, some new synthetically useful reactions employing Hantzsch ester were discussed which are summarized as following (Scheme 1):Scheme 11) The selective reduction of the exocyclic double bond of the 4-arylmethylene- and 4-alkylidene-4H-isoxazol-5-ones and 4-arylmethylene-4H- pyrazol- 5-ones was achieved by using Hantzsch 1, 4-dihydropyridine as the reducing agent in ethanol. This protocol could also be used for the selective reduction of the endocyclic double bond of the 3-electron withdrawing group substituted coumarins. This method is clean, mild, and efficient.2) ZrCl₄ / HEH was found to be a selective and efficient reagent combination for the direct reductive amination of electron rich aldehydes and ketones with weakly basic amines after scanning various catalysts such as InCl₃, BiCl₃, CF₃COOH and so on. As HEH and ZrCl₄ are both mild, inexpensive nontoxic reagents, this method is also advantageous in terms of mildreaction conditions, ease of handling and low cost. Furthermore, we also extended the use of Hantzsch ester to a tandem reductive animation/ lactamization procedure.3) On the basis of the above results, We investigated the reaction of Hantzsch ester with azides and discovered the azidoarenes could be selectively reduced to the corresponding amines by Hantzsch ester in the presence of catalytic Pd/C. The advantages of this mehtod include: operational simplicity, environmental acceptability, mild reaction conditions and reusability of the catalyst.4) A novel ring contraction rearrangement of Hantzsch 1,4-Dihydrpyridines (DHPs) was found to take place by using OxoneR as the oxidant, leading to the formation of highly poly-substituted furans. This method provides a convenient approach for the construction of multi-substituted furan ring from easy available starting materials DHPs. Other oxidants containing peroxyl-bond, such as H2O2, MCPBA and peroxy acetic acid, failed to generate the same results.