New efficient synthesis of polysubstituted 3,4-dihydroquinazolines and 4H-3,1-benzothiazines through a Passerini/Staudinger/aza-Wittig/addition/nucleophilic substitution sequence

• Long Zhao,
• Mao-Lin Yang,
• Min Liu and
• Ming-Wu Ding

Beilstein J. Org. Chem. 2022, 18, 286–292, doi:10.3762/bjoc.18.32

• /addition/nucleophilic substitution reactions. Keywords: aza-Wittig reaction; 3,4-dihydroquinazoline; 4H-3,1-benzothiazine; nucleophilic substitution; Passerini reaction; Staudinger reaction; Introduction The chemistry of 3,4-dihydroquinazolines and 4H-3,1-benzothiazines is of constant interest owing to

• protein cleaving enzyme 1 (BACE-1) inhibitive [6], and cholinesterase enzyme inhibitive activities [7]. The 3,4-dihydroquinazoline skeleton also exists in some natural products such as vasicine and vasicoline [8]. Some 4H-3,1-benzothiazine derivatives have also received attention due to their good

• biological activities, including anticancer [9], neuroprotective [10], antiproliferative and antifungal activities [11]. Due to the significant bioactive properties of the 3,4-dihydroquinazoline and 4H-3,1-benzothiazine moieties, many preparation procedures have appeared in the literature for the synthesis

Synthesis of dihydroquinazolines from 2-aminobenzylamine: N³-aryl derivatives with electron-withdrawing groups

• Nadia Gruber,
• Jimena E. Díaz and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2018, 14, 2510–2519, doi:10.3762/bjoc.14.227

• pharmacological interest. For example, vasicine is a 3,4-dihydroquinazoline alkaloid isolated from natural sources with antitumor activity [1]. Vasicine and deoxyvasicine are also potent butyrylcholinesterase (BChE) inhibitors [2]. Some synthetic derivatives containing the dihydroquinazoline scaffold have shown

• , some ruthenium complexes bearing a 3,4-dihydroquinazoline ligand have been studied as hydrogenation-transfer catalysts, showing good to excellent activity for the reduction of ketones [17]. In the context of our research on heterocyclic amidine N-oxides [18][19][20][21][22], we recently prepared some

• condensation position [48][49][50]. An exception to this is the recently reported synthesis of 3-(m-nitrophenyl)-5-nitro-3,4-dihydroquinazoline from m-nitroaniline and 1,3-dioxolane in the presence of strong protic acids [51]. In a related methodology, the ring closure of N-aryl-2-ABA is promoted by formic

Syntheses of 3,4- and 1,4-dihydroquinazolines from 2-aminobenzylamine

• Jimena E. Díaz,
• Silvia Ranieri,
• Nadia Gruber and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2017, 13, 1470–1477, doi:10.3762/bjoc.13.145

• , entries 4 and 8). Next, the conversion of N-(2-aminobenzyl)acetamide (4a) into 2-methyl-3,4-dihydroquinazoline (1a) was chosen for the optimization of the reaction conditions for the synthesis of compounds 1. No background reaction was observed when heating a solution of compound 4a in chloroform for 10

• 2-tert-butyl-3,4-dihydroquinazoline (1d, Table 4, entries 7 and 8), with loss of one N-substituent. A possible explanation is that the reaction conditions required in those cases due to steric hindrance bring about a competitive elimination reaction. Finally, as already mentioned, 1,4

Multicomponent reactions in nucleoside chemistry

• Mariola Koszytkowska-Stawińska and
• Włodzimierz Buchowicz

Beilstein J. Org. Chem. 2014, 10, 1706–1732, doi:10.3762/bjoc.10.179

• of cycloadducts 108 and 109 in molar ratios varied from 1:1 to 12:1. Compounds 108 were inactive against Aspergillus fumigatus or Candida albicans at concentration of 125 µg/mL. Nucleoside analogs 110 with the 3,4-dihydroquinazoline-derived nucleobase were obtained by Siddiqui et al. under microwave