Microwave-assisted synthesis of 2-substituted 4,5,6,7-tetrahydro-1,3-thiazepines from 4-aminobutanol

• María C. Mollo,
• Natalia B. Kilimciler,
• Juan A. Bisceglia and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2020, 16, 32–38, doi:10.3762/bjoc.16.5

• alcohols promoted by trimethylsilyl polyphosphate (PPSE) in solvent-free conditions allowed for the synthesis of several hitherto unreported seven-membered iminothioethers bearing 2-aryl, alkenyl, aralkyl and alkyl substituents. The cyclodehydration reaction is likely to involve an SN2-type displacement

• and affords good to excellent yields of the desired heterocycles in very short reaction times. Keywords: cyclodehydration; medium-size heterocycles; microwaves; PPSE; tetrahydrothiazepines; Introduction Thiazolines (4,5-dihydrothiazoles) are widely studied heterocycles due to their multiple

• Mitsunobu conditions led exclusively to the pyrrolidine derivative (76%) [32]. Therefore, the few literature examples reported until now are either complicated by side reactions or involve long reaction times and/or modest yields. Polyphosphoric acid (PPA) esters PPE (ethyl polyphosphate) and PPSE

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

• reaction promoted by trimethylsilyl polyphosphate (PPSE) is also proposed on the basis of literature data and our experimental observations. Keywords: cyclodehydrations; dihydroquinazolines; microwaves; nitrilium ions; PPSE; SNAr; Introduction Dihydroquinazolines (DHQs) represent heterocyclic cores of

• -aryl-2-iminoazacycloalkanes [84] and 2-oxazolines or their higher homologues [85], using polyphosphoric acid esters PPE (ethyl polyphosphate) [86] and PPSE (trimethylsilyl polyphosphate) [87] under microwave irradiation. PPE and PPSE are aprotic irreversible dehydrating agents of the Lewis acid-type

• low basicity of the dihydroquinazoline, which is not extracted in the acidic aqueous phase using the classical work-up procedure for PPE [41]. It had previously been reported that PPSE is a more efficient cyclization agent than PPE, allowing to perform some conversions that cannot be achieved by the

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

• -aminobenzophenone, 2-nitrobenzyl bromide, among others, which require an additional reduction step [17][18][29][49][50][51]. Ethyl polyphosphate (PPE) and trimethylsilyl polyphosphate (PPSE) are mild irreversible dehydrating agents of the Lewis acid type. They have found application for synthetically useful

• reported the MW-assisted synthesis of 1,4,5,6-tetrahydropyrimidines and their homologues by cyclodehydration reactions promoted by polyphosphoric acid (PPA) esters PPE and PPSE [58][59][60]. This strategy was successfully applied to the synthesis of 1-aryl-2-imino-1-azacycloalkanes [61], 2-oxazolines, 5,6

• minutes at 130 °C under MW irradiation in a closed vessel. Using a solution of PPSE in DCM as cyclodehydrating agent, after 30 minutes of reaction under reflux using conventional heating compound 1a was obtained in 86% yield. Analogous results were obtained using either PPE/CHCl3 or PPSE/CH2Cl2 under

Microwave-assisted cyclizations promoted by polyphosphoric acid esters: a general method for 1-aryl-2-iminoazacycloalkanes

• Jimena E. Díaz,
• María C. Mollo and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2016, 12, 2026–2031, doi:10.3762/bjoc.12.190

• trimethylsilyl polyphosphate (PPSE) in solvent-free conditions allowed for the synthesis of 1-aryl-2-iminopiperidines and hitherto unreported 1-aryl-2-iminoazepanes. The cyclization reaction involves good to high yields and short reaction times, and represents a novel application of PPA esters in heterocyclic

• synthesis. Keywords: cyclic amidines; medium size heterocycles; microwaves; PPE; PPSE; Introduction The synthesis of new nitrogen heterocycles has a great interest in medicinal chemistry since they are part of many drugs and represent structures with a wide therapeutic potential [1][2]. 2

• considerably lower nucleophilicity of the arylamino group, procedures for N-alkyl or N-unsubstituted 2-iminoazacycloalkanes are usually not suitable for the synthesis of N-aryl derivatives. Ethyl polyphosphate (PPE) and trimethylsilyl polyphosphate (PPSE) are mild irreversible dehydrating agents of the Lewis

Amyloid-β probes: Review of structure–activity and brain-kinetics relationships

• Todd J. Eckroat,
• Abdelrahman S. Mayhoub and
• Sylvie Garneau-Tsodikova

Beilstein J. Org. Chem. 2013, 9, 1012–1044, doi:10.3762/bjoc.9.116

• (98) were prepared and studied for Aβ imaging [73][74][75]. The simple two-step synthesis of 97 used polyphosphoric acid trimethylsilyl ester (PPSE) catalyzed condensation of 4-fluoro-2-aminophenol (112) with a cinnamic acid 113 to give the benzoxazole core followed by conversion to the primary amine