A New Method For The Construction Of Thiazole And Urea Compounds

Thiazole and urea derivatives were found wide applications in agrochemicals,pharmaceuticals,and materials science.The most general synthetic approaches to thiazole moiety involves the following methods:（a）condensation of 2-aminothiophenols with aldehydes.（b）transitional-metal-catalyzed cyclization reaction of o-haloanilines with isothiocyanates.（c）intramolecular cyclization of N-aryl thioureas.Additionally,the direct oxidative desulfurization of thioureas to ureas using KMn O₄,H₂O₂ and KICl₂as the oxidants has been demonstrated thus far.However,many of these procedures are associated with one or more disadvantages such as unavailable precursors,multistep processes,low yield and environmental pollution.Therefore,it is highly desirable to develop more efficient,environmental friendly,and convinent synthetic methods for the synthesis of thiazole and urea derivatives.Copper salts have been widely used as versatile catalysts for various organic transformations in synthetic community due to their characters of low cost,low toxicity and abundance.Recently,copper-catalyzed C-H bonds activation has emerged as a powerful strategy for the construction of heterocycle compounds.Since the twelve principles of“green chemistry”were proposed in the 1990s,chemists both in academia and industry have tried their best to follow them in chemical reactions.As a kind of green source of energy,visible light is generally regarded as a perfect promoter of organic transformations.Visible light photoredox catalysis is a versatile,environmentally friendly and powerful synthetic tool and has attracted extensive attention in the field of synthetic chemistry.Visible-light induced oxidation is an ideal choice for C-H/S-H cross-dehydrogenative coupling（CDC）sulfenylation reactions.Meanwhile,visible-light photoredox catalysis together with O₂ as a green and mild oxidant in aerobic oxidative tranformations has attracted significant attention.With our growing interest in organometallic chemistry and photochemistry,we proposed the following novel strategies for the synthesis of thiazole and urea derivatives.（1）A copper-catalyzed tandem process has been initially developed for the formation of2-thio-substituted benzothiazoles derivatives using readily available,cheap and easy-to-handle carbon disulfide as a building block.Most attractively,in this process three chemical bonds were formed in a one-pot organic transformation using a single copper catalyst.We anticipate that this strategy will open a new avenue for the synthesis of sulfur-containing heterocycles and may also find broad applicability in pharmaceutical chemistry and synthetic organic chemistry.（2）An efficient and eco-friendly protocol for the construction of naphtho[2,1-d]thiazol-2-aminesthroughvisible-lightphotoredox-catalyzed cross-dehydrogenative coupling reactions between 2-isothiocyanatonaphthalenes and amines was established.In this reaction,the new C-N and C-S bonds are formed simultaneously in a single step.This new method provides a straightforward approach for constructing valuable sulfur-containing compounds.（3）A green and efficient visible-light promoted oxidative desulphurisation protocol has been proposed for the construction of unsymmetrical ureas under mild conditions with broad substrate scope and good functional group tolerance.Most appealingly,the reaction can proceed smoothly without adding any strong oxidants.