5-Aminopyrazole as precursor in design and synthesis of fused pyrazoloazines

• Ranjana Aggarwal and
• Suresh Kumar

Beilstein J. Org. Chem. 2018, 14, 203–242, doi:10.3762/bjoc.14.15

• the presence of EDCl, DMAP and HOBt in N,N-dimethylformamide at room temperature for the synthesis of the corresponding amide derivatives 218 (Scheme 58). Song et al. [134] explored the synthesis of pyrazolo[3,4-d]pyrimidine derivatives 221 through the intermediacy of amidines 219 obtained by reaction

• of 5-amino-4-cyanopyrazole 208 with N,N-dimethylformamide dimethyl acetal (DMFDMA) in acetonitrile at reflux temperature. Amidines 219 were condensed with appropriate 2-amino-5-subsitituted-1,3,4-thiadiazoles 220 under microwave irradiation in acetic acid for the generation of the desired pyrazolo

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

• effort has been devoted to the development of efficient, general and expeditious methods for their synthesis [1][2]. Cyclic amidines are compounds of interest due to their multiple pharmacological properties, some of which derive from their interaction with a specific receptor [3][4]. Six-membered

• heterocylic amidines (1,4,5,6-tetrahydropyrimidines) display biological activity as anthelmintics used in medical practice (pyrantel, morantel and oxantel) [5][6], nicotinic agonists [7], antidepressants [8] and selective inhibitors of M1 acetylcholine receptors [9][10], among others. Their benzannulated

• heterocycles. Many methods use 2-aminobenzylamine (2-ABA) that reacts with amidines, carboxylic acids, orthoformates, or aldehydes in oxidative conditions to yield N-unsubstituted dihydroquinazolines [11][16][26][27][28][29][30][31][32][33][34][35]. A different approach is based on the heterocyclization of

A practical and efficient approach to imidazo[1,2-a]pyridine-fused isoquinolines through the post-GBB transformation strategy

• Taofeng Shao,
• Zhiming Gong,
• Tianyi Su,
• Wei Hao and
• Chao Che

Beilstein J. Org. Chem. 2017, 13, 817–824, doi:10.3762/bjoc.13.82

• hand, we then set out to explore the reaction scope for the library generation of structurally diverse imidazo[1,2-a]pyridine-fused isoquinolines and the results are collected in Table 2. Initially, several GBB adducts 4 were synthesized through GBB reaction of amidines 1, substituted 2

Regiochemistry of cyclocondensation reactions in the synthesis of polyazaheterocycles

• Patrick T. Campos,
• Leticia V. Rodrigues,
• Andrei L. Belladona,
• Caroline R. Bender,
• Juliana S. Bitencurt,
• Fernanda A. Rosa,
• Davi F. Back,
• Helio G. Bonacorso,
• Nilo Zanatta,
• Clarissa P. Frizzo and
• Marcos A. P. Martins

Beilstein J. Org. Chem. 2017, 13, 257–266, doi:10.3762/bjoc.13.29

• ] and aromatic amidines resulted in glyoxalate-substituted pyrido[1,2-a]pyrimidinone, thiazolo[3,2-a]pyrimidinone and pyrimido[1,2-a]benzimidazole. Pyrazinones and quinoxalinones were obtained through the reaction of these glyoxalates with ethylenediamine and 1,2-phenylenediamine derivatives. On the

• other hand, the reaction of glyoxalates with amidines did not lead to the formation of imidazolones, but rather N-acylated products were obtained. All the products were isolated in good yields. DFT-B3LYP calculations provided HOMO/LUMO coefficients, charge densities, and the stability energies of the

• functionalized heterocycles can also lead to the formation of polyazaheterocycles. Our research group has reported the synthesis of ethyl 5-carbonylpyrimidine-4-carboxylates from unsymmetrical enaminodiketones and amidines and their application in the preparation of pyrimido[4,5-d]pyridazin-8(7H)-ones [8]. One

p-Nitrophenyl carbonate promoted ring-opening reactions of DBU and DBN affording lactam carbamates

• Madhuri Vangala and
• Ganesh P Shinde

Beilstein J. Org. Chem. 2016, 12, 2086–2092, doi:10.3762/bjoc.12.197

• with a large substrate scope. Keywords: carbonates; DBN; DBU; lactams; p-nitrophenyl; Introduction Among various organic bases, amidines such as DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) and DBN (1,5-diazabicyclo[4.3.0]non-5-ene) having an imino group attached to the α-carbon of the amine are

• synthetically useful and strong neutral bases. Besides, DBU and DBN catalyze various organic reactions such as dehydrohalogenations [1], carbonylations [2], amidations [3] and Baylis–Hillman reactions [4]. These bicyclic amidines have been thought to be non-nucleophilic bases, but meanwhile numerous examples

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

• 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

• -Iminoazacycloalkanes are cyclic amidines where the formally sp2 nitrogen is exocyclic. These compounds have been described as selective inhibitors of the inducible form of human nitric oxide synthase (iNOS), which catalyzes the reaction to form nitric oxide via the oxidation of L-arginine to L-citrulline [3][4][5][6

• of conventional heating [17]. In previous work, we reported the microwave-assisted synthesis of 5 to 8 membered cyclic amidines by cyclodehydration of N-aryl-N´-acyl-1,n-alkanediamines (n = 2–5) promoted by polyphosphoric acid (PPA) esters PPE and PPSE (Scheme 1, reaction 1) [41][42][43]. In this

One-pot synthesis of tetracyclic fused imidazo[1,2-a]pyridines via a three-component reaction

• Bo Yang,
• Chuanye Tao,
• Taofeng Shao,
• Jianxian Gong and
• Chao Che

Beilstein J. Org. Chem. 2016, 12, 1487–1492, doi:10.3762/bjoc.12.145

• scaffolds can be constructed in great diversity by a multicomponent reaction of amidines, aldehydes and isocyanides. This MCR, a variant of the Ugi reaction [24][25], was discovered independently by three groups and is known as the Groebke–Blackburn–Bienaymé (GBB) reaction [26][27][28][29]. The reaction

• involves a formal [4 + 1] cycloaddition of isocyanides [30] and imines, generated from the amidines and aldehydes, allowing straightforward access to diverse imidazo[1,2-x]azines [31][32][33]. In view of the significance of the GBB reaction and the imidazo[1,2-a]pyridine core structure, the further

A convenient four-component one-pot strategy toward the synthesis of pyrazolo[3,4-d]pyrimidines

• Mingxing Liu,
• Jiarong Li,
• Hongxin Chai,
• Kai Zhang,
• Deli Yang,
• Qi Zhang and
• Daxin Shi

Beilstein J. Org. Chem. 2015, 11, 2125–2131, doi:10.3762/bjoc.11.229

• -carbonitrile with amides [18][19][20][21], carboxylic acids [22][23][24], amidines [25][26], nitriles [27][28], ketones [29][30] and halohydrocarbon [31], the cyclization of 5-aminopyrazole-4-carboxamides with amides [32], ureas [33][34][35][36], esters [37][38][39] and acyl chloride [40], and the reaction of

Synthesis of α-amino amidines through molecular iodine-catalyzed three-component coupling of isocyanides, aldehydes and amines

• Praveen Reddy Adiyala,
• D. Chandrasekhar,
• Jeevak Sopanrao Kapure,
• Chada Narsimha Reddy and
• Ram Awatar Maurya

Beilstein J. Org. Chem. 2014, 10, 2065–2070, doi:10.3762/bjoc.10.214

• the synthesis of α-amino amidines has been developed using a molecular iodine-catalyzed three-component coupling reaction of isocyanides, amines, and aldehydes. The presented strategy offers the advantages of mild reaction conditions, low environmental impact, clean and simple methodology, high atom

• economy, wide substrate scope and high yields. Keywords: α-amino amidines; iodine; isocyanide; multicomponent reaction; Ugi reaction; Introduction Amidines are a class of organic compounds exhibiting a variety of biological activity that makes them potential candidates for drug development and discovery

• [1][2][3][4][5]. Simple amidines are generally synthesized from their corresponding nitriles either by the Pinner reaction [6] or by the thioimidate route [7]. Recently, much attention was given to the development of new routes for the synthesis of substituted amidines [8][9][10][11]. Even if these

Use of activated enol ethers in the synthesis of pyrazoles: reactions with hydrazine and a study of pyrazole tautomerism

• Denisa Tarabová,
• Stanislava Šoralová,
• Martin Breza,
• Marek Fronc,
• Wolfgang Holzer and
• Viktor Milata

Beilstein J. Org. Chem. 2014, 10, 752–760, doi:10.3762/bjoc.10.70

• trifunctional electrophiles and are useful building blocks for the introduction of a three carbon fragment into the resulting molecule. Thus, the reaction of enol ethers with hydrazines produces pyrazoles, with amidines pyrimidines, with hydroxylamine isoxazoles, and with anilines quinolines/ones are formed [2

Aminofluorination of 2-alkynylanilines: a Au-catalyzed entry to fluorinated indoles

• Antonio Arcadi,
• Emanuela Pietropaolo,
• Antonello Alvino and
• Véronique Michelet

Beilstein J. Org. Chem. 2014, 10, 449–458, doi:10.3762/bjoc.10.42

• and alkynyl phenylhydrazones, respectively. Propargyl amidines were converted into 5-fluoromethylimidazoles in the presence of Selectfluor under gold(I) catalysis [34][35][36] through a cascade cyclization/fluorination process [37]. Following our previous work on gold catalysts (Scheme 1) [38], we

Organobase-catalyzed three-component reactions for the synthesis of 4H-2-aminopyrans, condensed pyrans and polysubstituted benzenes

• Moustafa Sherief Moustafa,
• Saleh Mohammed Al-Mousawi,
• Maghraby Ali Selim,
• Ahmed Mohamed Mosallam and
• Mohamed Hilmy Elnagdi

Beilstein J. Org. Chem. 2014, 10, 141–149, doi:10.3762/bjoc.10.11

• esters are generated in these reactions by ring opening of 9a and 9b to yield the respective amidines 29a and 29b, which then cyclize to produce 30a and 30b. The latter compounds readily undergo autooxidation to form 31a and 31b (Scheme 8). Finally, the pyranopyrimidines 33a and 33b were efficiently

An overview of the synthetic routes to the best selling drugs containing 6-membered heterocycles

• Marcus Baumann and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2013, 9, 2265–2319, doi:10.3762/bjoc.9.265

Copper-catalyzed aerobic aliphatic C–H oxygenation with hydroperoxides

• Pei Chui Too,
• Ya Lin Tnay and
• Shunsuke Chiba

Beilstein J. Org. Chem. 2013, 9, 1217–1225, doi:10.3762/bjoc.9.138

• tertiary C–H bonds, respectively (Scheme 1b) [8][9]. Stimulated by these remote sp3 C–H oxidation reactions using the nitrogen-centered radicals derived from amidines and ketimines, we became interested to utilize oxygen-centered radicals (O-radicals) for the sp3 C–H functionalization. In this context, we

• direct 1,4-dioxygenation of alkane 10 was demonstrated by using the present method. Further studies will be carried out to develop more robust and efficient catalytic aerobic radical transformations for polyol synthesis from rather simple alkanes. Aliphatic C–H oxidation with amidines and ketimines by

Synthetic studies towards bottromycin

• Stefanie Ackermann,
• Hans-Georg Lerchen,
• Dieter Häbich,
• Angelika Ullrich and
• Uli Kazmaier

Beilstein J. Org. Chem. 2012, 8, 1652–1656, doi:10.3762/bjoc.8.189

• ring system in a straightforward manner. Keywords: amidines; antibiotics; bottromycin; peptides; thiopeptides; Ugi reactions; Introduction Natural products are excellent sources as lead structures for the development of new antibiotics. Over millions of years microorganisms, such as bacteria and