multicomponent reactions ( mcrs ) have emerged as an efficient and dominant tool in modern synthetic organic chemistry allowing the facile creation of several new bonds in a one - pot reaction . clearly for multistep synthetic procedures , the number of reactions and purification steps is among the most significant criteria for the efficiency and feasibility of the process and should be as low as possible . therefore research in academia and industry has increasingly emphasized the use of mcrs as well as domino reaction sequences for a broad range of products [ 1 , 2 ] . ultrasound is widely used for improving the traditional reactions that use expensive reagents , strongly acidic conditions , long reaction times , and high temperatures unsatisfactory yields . 4-substituted 1,4-dihydropyridines ( 1,4-dhps ) are well known as ca channel blockers and emerged as one of the most important classes of drugs for the treatment of cardiovascular diseases , including hypertension [ 4 , 5 ] . in view of the importance of polyhydroquinoline derivatives , many classical methods for their synthesis were reported [ 611 ] using conventional heating and refluxing approaches in the presence of an organic solvent . these methods , however , involve long reaction times , harsh reaction conditions , and the use of a large quantity of volatile organic solvents and generally lead to low yields . therefore , it is necessary to develop an efficient and versatile method for the preparation of 1,4-dihydropyridines , and the progress in this field has been recently remarkable including the promotion of microwave , tmscl , ionic liquids [ 14 , 15 ] , polymers [ 16 , 17 ] , and yb(otf)3 . the multicomponent reactions are powerful tools in the modern drug discovery process and allow fast , automated , and high - throughput generation of organic compounds . the possibility of performing multicomponent reactions under solvent - free conditions with a heterogeneous catalyst could enhance their efficiency from an economic as well as an ecological point of view . in recent years heterogeneous catalysts herein , we would like to report an efficient and greener route for the synthesis of polyhydroquinolines from the reaction of readily available and nonexpensive starting materials ( dimedone , aromatic aldehydes , ethyl acetoacetate , ammonium acetate , and copper perchlorate hexahydrate ) under solvent - free conditions using ultrasonic irradiation . all melting points recorded are uncorrected , open capillary measurements , using sulphuric acid bath . nmr spectra were recorded on al-300f ( bruker ) ft nmr spectrophotometer using tetramethylsilane ( tms ) as internal standard . a mixture of aryl aldehyde ( 1  mmol ) , 5,5-dimethyl-1,3-cyclohexanedione ( 1  mmol ) , ethyl acetoacetate ( 1  mmol ) and ammonium acetate ( 1  mmol ) was added to cu(clo4)26h2o ( 15  mol% ) , and the reaction mixture was exposed to ultrasound irradiation 2040 min ( completion of the reactions was monitored by tlc ) . after the completion of reaction , the reaction mixture was diluted with ethyl alcohol and stirred for 10 minutes at 80c . the residue was filtered hot and kept at room temperature , and the resulting crystalline product was collected by filtration . the formation of products was confirmed by comparing the melting points and nmr data with authentic samples and literature data . 

 2,7,7-trimethyl-5-oxo-4-phenyl-1,4,5,6,7,8-hexahydroquinoline-3-carboxylic acid ethyl ester ( 1a)mp 202204c . ir ( kbr ) cm : 3287 , 3077 , 2964 , 1696 , 1610 . h - nmr ( cdcl3 )  : 0.93 ( 3h , s ) , 1.06 ( 3h , s ) , 1.20 ( 3h , t , j = 7.1  hz ) , 2.122.28 ( 4h , m ) , 2.34 ( 3h , s ) , 4.05 ( 2h , q , j = 7.1  hz ) , 5.06 ( 1h , s ) , 6.63 ( 1h , s ) , 7.077.12 ( 1h , m ) , 7.177.22 ( 2h , m ) , 7.277.32 ( 2h , m ) . ir ( kbr ) cm : 3287 , 3077 , 2964 , 1696 , 1610 . h - nmr ( cdcl3 )  : 0.93 ( 3h , s ) , 1.06 ( 3h , s ) , 1.20 ( 3h , t , j = 7.1  hz ) , 2.122.28 ( 4h , m ) , 2.34 ( 3h , s ) , 4.05 ( 2h , q , j = 7.1  hz ) , 5.06 ( 1h , s ) , 6.63 ( 1h , s ) , 7.077.12 ( 1h , m ) , 7.177.22 ( 2h , m ) , 7.277.32 ( 2h , m ) . 

 4-(4-methoxyphenyl)-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylic acid ethyl ester ( 1b)mp 257 - 258c . ir ( kbr ) cm : 3276 , 2956 , 1703 , 1648 , 1606 , 1496 , 1381 , 1215 , 1031 , 765 . h - nmr ( cdcl3 + dmso - d6 )  :  = 0.95 ( 3h , s ) , 1.09 ( 3h , s ) , 1.21 ( 3h , t , j = 7.2  hz ) , 2.012.10 ( 4h , m ) , 2.30 ( 3h , s ) , 3.70 ( 3h , s ) , 4.00 ( 2h , q , j = 7.2  hz ) , 4.80 ( 1h , s ) , 6.65 ( 2h , d , j = 7.3  hz ) , 7.10 ( 2h , d , j = 7.3  hz ) , 8.65 ( 1h , s ) . 
  mp 257 - 258c . ir ( kbr ) cm : 3276 , 2956 , 1703 , 1648 , 1606 , 1496 , 1381 , 1215 , 1031 , 765 . h - nmr ( cdcl3 + dmso - d6 )  :  = 0.95 ( 3h , s ) , 1.09 ( 3h , s ) , 1.21 ( 3h , t , j = 7.2  hz ) , 2.012.10 ( 4h , m ) , 2.30 ( 3h , s ) , 3.70 ( 3h , s ) , 4.00 ( 2h , q , j = 7.2  hz ) , 4.80 ( 1h , s ) , 6.65 ( 2h , d , j = 7.3  hz ) , 7.10 ( 2h , d , j = 7.3  hz ) , 8.65 ( 1h , s ) . 

 4-(4-fluorophenyl)-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylic acid ethyl ester ( 1f)mp 184 - 185c . ir ( kbr ) cm : 3292 , 2959 , 1696 , 1649 , 1608 , 1487 , 1380 , 1219 , 1025 , 764 . h - nmr ( cdcl3 )  : 0.92 ( 3h , s ) , 1.07 ( 3h , s ) , 1.18 ( 3h , t , j = 7.3  hz ) , 2.132.25 ( 4h , m ) , 2.38 ( 3h , s ) , 4.05 ( 2h , q , j = 7.33  hz ) , 5.02 ( 1h , s ) , 5.8 ( 1h , s ) , 6.856.89 ( 2h , m ) , 7.237.27 ( 2h , m ) . ir ( kbr ) cm : 3292 , 2959 , 1696 , 1649 , 1608 , 1487 , 1380 , 1219 , 1025 , 764 . h - nmr ( cdcl3 )  : 0.92 ( 3h , s ) , 1.07 ( 3h , s ) , 1.18 ( 3h , t , j = 7.3  hz ) , 2.132.25 ( 4h , m ) , 2.38 ( 3h , s ) , 4.05 ( 2h , q , j = 7.33  hz ) , 5.02 ( 1h , s ) , 5.8 ( 1h , s ) , 6.856.89 ( 2h , m ) , 7.237.27 ( 2h , m ) . 

 4-(2-chlorophenyl)-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylic acid ethyl ester ( 1k)mp 209 - 210c . ir ( kbr ) cm : 3063 , 2956 , 1721 , 1640 , 1611 , 1467 , 1384 , 1227 , 1021 , 745 . h - nmr ( cdcl3 + dmso - d6 )  :  = 0.95 ( 3h , s ) , 1.05 ( 3h , s ) , 1.20 ( 3h , t , j = 7.2  hz ) , 2.012.21 ( 4h , m ) , 2.40 ( 3h , s ) , 4.05 ( 2h , q , j = 7.2  hz ) , 4.60 ( 1h , s ) , 7.107.30 ( 4h , m ) , 7.60 ( 1h , s ) . ir ( kbr ) cm : 3063 , 2956 , 1721 , 1640 , 1611 , 1467 , 1384 , 1227 , 1021 , 745 . h - nmr ( cdcl3 + dmso - d6 )  :  = 0.95 ( 3h , s ) , 1.05 ( 3h , s ) , 1.20 ( 3h , t , j = 7.2  hz ) , 2.012.21 ( 4h , m ) , 2.40 ( 3h , s ) , 4.05 ( 2h , q , j = 7.2  hz ) , 4.60 ( 1h , s ) , 7.107.30 ( 4h , m ) , 7.60 ( 1h , s ) . in continuation of our work to develop new and ecofriendly synthetic methodologies [ 2023 ] , herein , we report an expedient protocol for the synthesis of polyhydroquinolines . the reactions were carried out at room temperature for 2040  min in the presence of 15  mol% of the copper perchlorate hexahydrate at 35  khz under ultrasound irradiation . to determine the amount of the catalyst in this reaction , benzaldehyde was used as one of the reactants for 20  min under ultrasound irradiation in the presence of varying mol% of the copper perchlorate hexahydrate separately . the best results were obtained using 15  mol% of the catalyst . using lesser amount of the catalyst resulted in lower yields , while higher amount of the catalyst did not affect reaction times and yields . in the absence of the catalyst , the yield was found to be very low . to verify the effect of ultrasound irradiation on this procedure , the synthesis of polyhydroquinolines was done in the presence of varying mol% of the copper perchlorate hexahydrate with and without ultrasound irradiation ( table 1 ) . in all reactions , it was found that the use of ultrasound leads to faster reaction and higher yields . so it shows that use of the ultrasound improves the rate of reaction and also yields of products formed . a wide range of substituted aldehydes were used to give excellent yield of products ( 1a1l ) ( table 2 ) . reactions were also performed using ethanol as a solvent , but the yield was less than the in solvent - free conditions . we have introduced a new and highly efficient catalyst , copper perchlorate hexahydrate , for the synthesis of polyhydroquinolines . the significant aspects of our methodology are efficiency , generality , high yield , short reaction time , low cost , cleaner greener reaction profile , ease of product isolation , the use of alternative source of energy , and ultimately conformity with the green chemistry protocols .
copper perchlorate hexahydrate as an efficient catalyst was used for the synthesis of polyhydroquinolines by four - component condensation reaction of aldehyde , ethyl acetoacetate , dimedone , and ammonium acetate in excellent yields and short reaction times at room temperature under ultrasound irradiation . 
 this novel synthetic method is especially favoured because it provides a synergy between copper perchlorate hexahydrate and ultrasound irradiation which offers the advantages of high yields , short reaction times , simplicity , and easy workup compared to the conventional methods reported in the literature .