【作者】 王伟；

【导师】 徐元清； 徐浩；

【作者基本信息】 河南大学 ， 有机化学， 2017， 硕士

【摘要】 含氮杂环化合物在功能材料、染料、医药、农药等多领域有着非常广泛的应用;尤其在医药、农药领域,60%以上的医药、农药分子是氮杂环分子,其地位无可替代。因此,寻找绿色、高效的催化体系,实现从简单底物出发合成氮杂环化合物,一直是合成领域的研究热点。传统的过渡金属催化和电加热合成含氮杂环化合物的方法金属残留严重、能耗大,通过无金属、碱辅助、一锅法和光催化的绿色合成手段可以有效缓解上述问题。我们围绕1,2,4-噁二唑和苯并咪唑的绿色合成进行了研究,并取得了如下主要成果:以简单底物出发合成1,2,4-噁二唑通常要以脒肟为底物或者中间体,已报道的合成方法大多条件苛刻。例如,以脒肟和羧酸反应生成1,2,4-噁二唑需要添加强脱水剂;和醛反应需要添加强氧化剂或者在微波条件下反应。我们在碱辅助条件下以简单的底物腈、醛及盐酸羟胺,氮气氛围下一锅法合成了 3,5-二取代-1,2,4-噁二唑。反应底物简单易得、无需添加额外氧化剂、不需要提取中间体,对各种芳香腈和醛都有较高的普适性,并且产率最高可以达到93%。对环境友好,与之前的方法相比体现出了较大的经济和实用价值。我们提出并验证了该化合物合成的新的反应机理,芳香醛很少报道作氧化剂,在我们的反应中芳香醛既作反应物参与反应又做氧化剂氧化中间体,无需额外添加氧化剂就合成出了 1,2,4-噁二唑化合物。这样的反应方法对经济和环境都友好,符合绿色化学的要求。传统合成苯并咪唑方法通常需要添加强酸、过渡金属催化剂在加热下进行,反应条件相对苛刻。光催化是典型的绿色合成方法,室温下反应、副产物较少,不需要多么复杂的操作就可以很好的反应,并且可见光能源作为一种绿色的能源,温和的反应条件非常符合绿色化学的要求。以邻苯二胺与醛或醇在光催化下合成苯并咪唑已有报道。然而,醛在氧气或空气条件下容易氧化变质,影响反应效果。而邻苯二胺与醇的反应通常需要加入过渡金属催化剂。我们用有机光敏剂eosinY催化邻苯二胺和醇在氧气条件下反应生成取代的苯并咪唑类化合物。反应分为两步,醇先在光催化下氧化生成醛,随后和邻苯二胺反应生成相应的苯并咪唑化合物。反应条件温和,不需要添加金属催化剂,并且是以温和的氧气作为氧化剂,绿色环保。更多还原

【Abstract】 N-heterocyclic compounds are widely used in functional materials,dyes,pharmaceuticals,pesticides and other fields;The position of nitrogen heterocycles is irreplaceable,especially in the field of medicine and pesticide.More than 60%of the medicine and pesticide molecules are nitrogen-containing heterocyclic compounds.Therefore,looking for a green and efficient method for the synthesis of N-heterocyclic compounds from simple substrates has always been a hot topic in the synthesis field.The traditional method of transition-metal-catalyzed and electrically heated synthesis of N-heterocyclic compounds has the problem of metal residue and large energy consumption.Through the synthetic means of metal-free,alkali-assisted and photocatalytic green can effectively alleviate the above problems.In the synthesis of N-heterocyclic compounds,we have studied the green synthesis of 1,2,4-oxadiazole and benzimidazole by above means and achieved the following main achievements:Among the known synthetic strategies of 1,2,4-oxadiazoles,the most common approach is to utilize amidoximes as starting materials or intermediates;the.previous synthetic methods through this approach always need to be proceed under harsh conditions.For example,when carboxylic acid and amidoximes are used as the substrates to prepare 1,2,4-oxadiazoles,strong dehydrating agent are usually needed;When aldehydes and amidoximes are used as the substrates,oxidants or microwave conditions are usually needed.A simple base-mediated one-pot synthesis of 3,5-disubstituted 1,2,4-oxadiazoles from nitriles,aldehydes and hydroxylamine hydrochloride has been developed under of nitrogen atmosphere.This method has several advantages such as the substrates is simple,one-pot synthesis without separating intermediates.A variety of aromatic systems,including heterocyclic nitrile and aldehydes are preferred,the yield can be achieved 93%.Compared with the previous method,this method is environmentally friendly,and has great economic and practical value.We synthesized the 1,2,4-oxadiazole without extra oxidants or additives,and proposed a new reaction mechanism of the synthesis of the compound,Aromatic aldehydes are rarely reported as oxidants.In our reaction,aldehydes act as both substrates and oxidants.This reaction method is cost-effective,environmentally friendly;it is in line with the requirements of green chemistry.Traditionally,synthesis of benzimidazoles usually needed to add strong acid or transition metal as catalyst under heating,the reaction conditions are relatively harsh.Photocatalysis is a typically green synthetic method has the advantages such as room temperature reaction,less amount of by-products,easy to handle.And the application of visible light energy is consistent with the requirements of green chemistry.The synthetic methods of benzimidazole through photocatalysis has been reported before,which o-phenylenediamines and aldehydes or alcohols used as the substrates under photocatalytic conditions.However,aldehydes are easy to be oxidizede,leading to the formation of unwanted by-product.When o-phenylenediamines and alcohols are used as the substrates,transition-metal-catalysts are usually needed.We have developed a organic photosensitizer eosinY-catalyzed method for the synthesis of benzimidazole compounds from o-phenylenediamines and alcohols under metal-free and visible-light induced conditions,in which the oxygen act as oxidants.This reaction include two sequential procedures:oxidative dehydrogenation to alcohol to lead to aldehyde,treatment of aldehyde with o-phenylenediamine to form the corresponding benzimidazole compounds under photocatalyzed and oxygen-oxidized conditions.This method has the many advantages such as mild oxidant oxygen,metal-free catalyst and the mild and green reaction conditions.更多还原