Studies On Solvent-Free And Liquid-Phase Addition Reactions

For the stringent and growing environmental regulations,organic chemists are requested to develop clean,economical and environmental safer methodologies. Performing organic reactions with mechanochemical technique under solvent-free conditions is a very promising approach.The main work presented in this dissertation is about the investigation on cycloaddition reactions and asymmetric reaction carried out under mechanochemical conditions.And also,we studied the N-alkylation and N-arylation reaction of azodicarboxylate esters.1.We have developed the synthesis of trans-2-acyl-3-aryl/alkyl-2,3,6,7-tetrahydro-4(5H)-benzofuranone derivatives through the radical reactions of 1-(pyridin-2-yl)-enones with 1,3-cyclohexanediones mediated by Mn(OAc)₃·2H₂O.The present solvent-free radical reactions were very efficient, affording the unexpected products in as high as 91%yield under our ball-milling conditions.More importantly,the reversed regioselectivity of 1-(pyridin-2-yl)-enones was uncovered for the first time.Mn(OAc)₃·2H₂O played the role both as an oxidant and as a Lewis acid,and thus altered the reaction pathway of 1-(pyridin-2-yl)-enones.2.We have presented a practical method for the preparation of propargylic alcohols from terminal alkynes and carbonyl compounds promoted by KOH in the presence of 18-crown-6,and subsequent efficient cyclizations of propargylic alcohols with 2-naphthol catalyzed by InCl₃·4H₂O under the solvent-free ball-milling conditions.Ball milling exhibits its superiority over the reported methods in the preparation of propargylic alcohols and naphthopyran derivatives. The advantages of this procedure including avoidance of any solvent,mild condition,high yield,short reaction time and easy work-up procedure made the present method a convenient,effective and environmentally friendly one,which could serve as an attractive alternative to the traditional methodology.3.Chiral phosphoric acid mediated,solvent-free asymmetric Fridel-Crafts reactions of indols and imines have been carried out under solid-state mechanochemical conditions.In which,3,3'-(1-naphthyl) substituted chiral phosphoric acid was found to possess the best catalytic ability.Some other aspects such as the reaction temperature,amount of indols and the frequency of ball milling were also investigated.Under the Optimized reaction conditions,the addition products could be obtained in a short time with high yield and moderate enantiomeric excess.4.A simple and efficient method for the solvent-free synthesis of N-alkyl substituted hydrazines has been described.By direct thermal heating,N-alkylation reactions of 1,3-diketones andβ-keto esters with diethyl azodicarboxylate ester proceeded well in excellent yields.The products could serve as substrates for further preparation ofα-amino-1,3-dicarbonyl compounds.This method provided several advantages such as no usage of any solvent,being environmentally friendly, simple work-up procedure and high yields.5.We have developed an efficient catalytic system for preparing a variety of aryl-substituted hydrazines in up to 99%yield through the coupling of arylboronic acids with azodicarboxylate esters in the presence of the easily available catalyst[Cu(OH)·TMEDA]₂Cl₂.This N-arylation reaction of azodicarboxylate esters did not require protection with inert atmosphere because oxygen was not involved in the reaction.Moreover,the[Cu(OH)·TMEDA]₂Cl₂-catalyzed coupling reaction exhibited excellent selectivity of arylboronic acids for the N-arylation reaction over the homocoupling reaction.