Asymmetric Ugi/aza-Wittig Reactions Catalyzed By Anionic Stereogenic-at-cobalt Complexes

Oxazole compounds are a five membered heterocyclic compound containing N/O atoms.Some compounds containing oxazole rings can applied in fields such as medicine,pesticides and high temperature resistant materials.For example,2-aminooxazole has antiviral and antibacterial effects;Compounds containing benzoxazole in their molecules can be used to make high-temperature resistant materials;At the same time,compounds containing oxazole rings also have some biological activities and can be used in pesticide production and other aspects.Given that most of the previous exploration of oxazole compounds was methodological and did not focus on asymmetric synthesis,the development of chiral oxazole compounds has become a novel field at present.In this project,the multi-component asymmetric Ugi/aza-Wittig reaction catalyzed by anionic stereogenic-at-cobalt(III)complexes was developed.The chiral oxazole compounds were constructed from aldehydes,amines,carboxylic acids and triphenylphosphine isocyanates.This experiment first completed the optimization of reaction conditions,namely the screening of catalysts,reaction solvents,additives,and temperature.It was found that using the catalyst prepared from L-tert leucine and 3,5-tert butylsalicylaldehyde has the best performance,obtaining over thirty oxazole compounds with a yield of up to 60% and enantioselectivity of 86%.Subsequent studies on nonlinear effects have shown that the reaction conclusion presented in this experiment is a linear effect.Then,based on the above experimental results and previous literature,the reaction mechanism of this subject was speculated.Through the nucleophilic addition reaction between aldehyde and amine,the imine was activated by cobalt(III)anion and carboxylic acid to form an intermediate.After the isocyanate attack,the transition state was formed,and then the intra molecular aza Wittig reaction was carried out to remove triphenoxyphosphorus and generate oxazole compounds(products).Following the above experiments,the biological activities of Trichoderma viride,Fusarium graminearum,and Botrytis cinerea were tested,and the conclusion showed that chiral oxazole compounds can effectively inhibit the growth of fungal organisms.Through exploration and research on oxazole compounds,it has been found that oxazole compounds have potential pesticide application value.