Study On Value-added Conversions Of Glyoxal By Using Glyoxal Dimethyl Acetal As A Key Intermediate

Glyoxal is the simplest dialdehyde compound.The domastic total output is close to200,000 tons/year,and its price is RMB 7 000 per ton.As a bulky chemical,the downstream transformation of glyoxal is always needed as tighter profit margins and excess capacity.Glyoxal dimethyl acetal,as a downstream product of glyoxal,is mostly imported in the domestic market of China,the current market price is RMB 2 000 per kilogram.Because of the high cost of glyoxal dimethyl acetal,some Chinese companies are working hard in order to realize its industrial production in high quality with good economic benifit.It is expected that glyoxal dimethyl acetal will be soon commercially produced in China.It is worth to expore the value-added conversion of glyoxal based on the unique reactivity of glyoxal dimethyl acetal.In this paper,glyoxal dimethyl acetal is converted into some value-added chemicals,such as N-arylformamides,methyl phenylglycinate,carbazoles,indoles and N-alkylpyrrole-3-carboxylates,through simple oxidation,rearrangement,cyclization and other reactions.The research content of the paper is as follows:（1）Chemodivergent reactions of glyoxal dimethyl acetal and anilines were described,which were established on the controls of solvent,atmosphere,ratio of substrates.In the presence of O₂,glyoxal dimethyl acetal reacted with aniline to deliver N-arylformamides via a C-C bond cleavage reaction.However,Heyns rearrangement occurred and generated methyl phenylglycinate and dimethyl 2,2’-（phenylazanediyl）diacetate by performing the reaction in the absence of O₂.Substrates scope studies show that most of aniline can participate in this reaction,and some products have a certain scale of market demand,such condition-determined reactions not only offered the new way for value-added conversion of glyoxal dimethyl acetal but also provided efficient methods for the synthesis of N-arylformamides and methyl phenylglycinates.（2）Morita-Baylis-Hillman alcohol and acetate derivatives with acetal fragments were prepared by Morita-Baylis-Hillman reaction with glyoxal dimethanol and acrylate as raw materials under the catalysis of triethylenediamine.A variety of N-aryl/alkylβ-carbonylpyrroles can be efficiently synthesized from the reaction of Morita–Baylis–Hillman acetate and primary amine in the presence of potassium alum in ethanol through S_N2’substitution-cyclization-aromatization cascade reaction.Compared with previous works,this method has obvious advantages in safety,cost and environmental friendliness compared with the classical method reported in literature.Partially,substituted pyrrole has also been successfully used to prepare JMH-030,JMC-2004 and other bioactive molecules.（3）Morita-Baylis-Hillman adducts derived from glyoxal dimethyl acetal were used as 1,4-electrophiles to react with indoles,pyrroles,and phenylhydrazines.In the presence of different acid catalysts,many nitrogen heterocycles,such as carbazoles,indoles and1-phenyl-1,2-dihydropyridazines,could be prepared via[4+2]cyclization reactions.Particularly,Morita-Baylis-Hillman alcohols and their derivatives could react with indoles to form C2-and C3-carboxylated carbazoles depending on the reaction conditions used.Besides,this stratage could efficiently realized the synthesis of indoles and dihydropyridazines,which enriches the diversity of high value-added chemicals prepared from glyoxal dimethyl acetal derivatived from glyoxal.All the above works were carried out with glyoxal dimethyl alcohol as raw material,and the established reaction systems featured by simple operation and metal-free conditions.The obtained N-aryl/alkyl-carbonylpyrroles,N-phenylglycines,carbazoles and other products are all valuable N-containing compounds with a certain scale of market demand.Our works not only simplified the synthesis of target compounds,but also greatly enriched the diversity of downstream products of glyoxal,and thus significantly boosted the development of glyoxal chemisty.