Sono-thermal oxidation of dihydropyrimidinones

Abstract

Combination of ultrasound and heat has been used for the oxidation of some ethyl 3,4-dihydropyrimidin-2(1H)-one-5-carboxylates to their corresponding ethyl pyrimidin-2(1H)-one-5-carboxylates by using potassium peroxydisulfate in aqueous acetonitrile. An ultrasonic probe of 24 kHz frequency has been used for this study. Whereas the use of ultrasound increases the rate of reactions compared with reactions at reflux conditions, the nature of 4-substituent on the dihydropyrimidinone ring affects also the rate of reaction.

Study of the Synthesis of Some Biginelli-type Products Catalyzed by Nano-ZrO2

“…Our procedure is simple but effective for the synthesis of the some DHPMs. Comparison of these data with the data of SO 4 2− /ZrO 2 shows that using the nano-ZrO 2 is a simple and mild method which has advantages such as excellent yields, short reaction times and low cost.…”

“…They prepared sulfated zirconia (SO 4 2− /ZrO 2 ) by a multistep procedure and applied it as an acid catalyst replacement for common acid substances in the Biginelli reaction [13]. In this method a mixture of catalyst (50 mg, 0.26 mmol vis.…”

In situ formed tert-butyl hypoiodite as an efficient oxidant for rapid, room temperature, metal-free aromatization of Biginelli 3,4-dihydropyrimidin-2(1H)-ones under basic conditions

“…Product yields ranged from 68-96%, except for compound 5 ( Table 5, Entry 4), due to the presence of the ortho-nitro group on the aromatic ring, which gave product at a yield of 55%. Both electron-withdrawing (Table 5, Entries 4-6) and electron-donating substituents (Table 5, Entries 7,8,[15][16][17]24) on the aromatic ring were well tolerated and had no considerable influence on the reaction rate. The oxidation of all sterically constrained derivatives Shanmugam et al 13 provided the explanation that this phenomenon was caused by the tautomerization of N1-H to N3 in a solution of N(1)-alkyl unsubstituted dehydrogenated product.…”

“…10,11 Nevertheless, over the past two decades, different reagents and methods have been used, more or less successfully, for this type of reaction. 22 UV light induced oxidation/Ar, 7,8 ultrasound-assisted oxidation/K 2 S 2 O 8 , 23 aerobic oxidative dehydrogenation/NHPI/Co II , 24 using Ca(OCl) 2 in aqueous media oxidation, 6 photochemical oxidation using Re(I)complex, 25 CAN/HCl, 26 microwave-assisted oxidation/I 2 , 27 light-induced free radical oxidation, 28 dehydrogenation with 1,4-bis(triphenylphosphonium)-2-butene peroxodisulfate 29 and others. [30][31][32][33] However, despite best efforts, none of these methods have been found to be ideal with respect to prolonged reaction time, low yield, use of toxic reagents, complicated product isolation, etc.…”

Light-induced Free Radical Oxidation of 2-Oxo-1,2,3,4-tetrahydropyrimidines

“…Recently we have reported the oxidation of various 4-arylsubstituted 5-acetyl-and 5-carboethoxy-2-oxo-1,2,3,4-tetrahydropyrimidines (THPMs) under thermal [24] and sonothermal conditions [25,26], and microwave irradia-tion [27] by potassium peroxydisulfate (PPS) in aqueous acetonitrile, and also by exposing them to UV light in chloroform solution [28,29]. The results obtained by the reaction in the presence of PPS indicate that in situ formed hydroxyl radicals are responsible for the removal of the 4-hydrogen in the rate-determining step.…”