Reductions of aldehydes and ketones with a readily available N-heterocyclic carbene borane and acetic acid

• Vladimir Lamm,
• Xiangcheng Pan,
• Tsuyoshi Taniguchi and
• Dennis P. Curran

Beilstein J. Org. Chem. 2013, 9, 675–680, doi:10.3762/bjoc.9.76

• measurement of the nucleophilicity parameter, N [14]. By this measure, NHC-boranes are among the best neutral hydride donors known, more reactive than distant relatives such as silanes, stannanes, and dihydropyridines, and more reactive even than their amine-borane cousins [15][16][17][18][19]. Despite being

Intramolecular carbolithiation of N-allyl-ynamides: an efficient entry to 1,4-dihydropyridines and pyridines – application to a formal synthesis of sarizotan

• Wafa Gati,
• Mohamed M. Rammah,
• Mohamed B. Rammah and
• Gwilherm Evano

Beilstein J. Org. Chem. 2012, 8, 2214–2222, doi:10.3762/bjoc.8.250

• 10.3762/bjoc.8.250 Abstract We have developed a general synthesis of polysubstituted 1,4-dihydropyridines and pyridines based on a highly regioselective lithiation/6-endo-dig intramolecular carbolithiation from readily available N-allyl-ynamides. This reaction, which has been successfully applied to the

• formal synthesis of the anti-dyskinesia agent sarizotan, further extends the use of ynamides in organic synthesis and further demonstrates the synthetic efficiency of carbometallation reactions. Keywords: carbolithiation; carbometallation; dihydropyridines; organolithium reagents; pyridines; sarizotan

• carbolithiation of ynamides, which may provide an interesting entry to highly functionalized 1,4-dihydropyridines [27][28][29] and pyridines [30][31][32][33], most useful building blocks in organic synthesis and medicinal chemistry as well. Our strategy is summarized in Scheme 1 and is based on the following

Enaminones in a multicomponent synthesis of 4-aryldihydropyridines for potential applications in photoinduced intramolecular electron-transfer systems

• Nouria A. Al-Awadi,
• Maher R. Ibrahim,
• Mohamed H. Elnagdi,
• Elizabeth John and
• Yehia A. Ibrahim

Beilstein J. Org. Chem. 2012, 8, 441–447, doi:10.3762/bjoc.8.50

• resulted in easy access to 1,4-dihydropyridines with different substituents at the 1-, 3-, 4- and 5-positions. Microwaves improved the reaction yield, reducing also considerably the reaction time and the amount of solvent used. Chiral primary amines gave chiral 1-substituted-1,4-dihydropyridines. The 4-(1

• -naphthyl) and 4-(phenanthren-9-yl)dihydropyridine derivatives exhibited an interesting photoluminescence behavior, which suggests their potential application as suitable photoinduced intramolecular electron-transfer systems. Keywords: enaminones; 1,4-dihydropyridines; microwaves; multi-component reactions

• prepared by various methods, for example, 1 is readily obtained in excellent yield by the condensation of different methylketones with dimethylformamide dimethylacetal (DMFDMA) [16][17]. In this work we investigated the potential utility of 1 in a three-component synthesis of dihydropyridines (DHP) (Scheme

Regioselectivity in the multicomponent reaction of 5-aminopyrazoles, cyclic 1,3-diketones and dimethylformamide dimethylacetal under controlled microwave heating

• Kamal Usef Sadek,
• Ramadan Ahmed Mekheimer,
• Tahany Mahmoud Mohamed,
• Moustafa Sherief Moustafa and
• Mohamed Hilmy Elnagdi

Beilstein J. Org. Chem. 2012, 8, 18–24, doi:10.3762/bjoc.8.3

• pyrazoloquinolinones (Hantzsch-type dihydropyridines). On the other hand, the use of sonication at room temperature under neutral conditions favours the formation of isomeric pyrazolo[5,1-b]quinazolin-8(4H)-ones (Biginelli-type dihydro-pyrimidines) [9]. Employing more nucleophilic bases to catalyse the reaction

Reductive amination with zinc powder in aqueous media

• Giovanni B. Giovenzana,
• Daniela Imperio,
• Andrea Penoni and
• Giovanni Palmisano

Beilstein J. Org. Chem. 2011, 7, 1095–1099, doi:10.3762/bjoc.7.125

• ], Zn(BH4)2/ZnCl2 [10], NaBH4/Mg(ClO4)2 [11], electrochemistry [12], 1,4-dihydropyridines [13][14], Ti(OiPr)4-PMHS [15], NaBH4-CoCl2 [16], iPrOH/RuCl(PPh3)2 [17], BH3·Me2S [18], PhSiH3-Bu2SnCl2 [19], and Zn/HCOONH4 [20]. Although the choice of reagents for reductive amination is quite large, a closer

Fused bicyclic piperidines and dihydropyridines by dearomatising cyclisation of the enolates of nicotinyl-substituted esters and ketones

• Heloise Brice,
• Jonathan Clayden and
• Stuart D. Hamilton

Beilstein J. Org. Chem. 2010, 6, No. 22, doi:10.3762/bjoc.6.22

• related cyclisations of pyridyl-, nicotinamide- and isonicotinamide-containing carbanions yield related bicyclic dihydropyridines [33][34]. While reactive carbanions derived from allyl or benzyllithiums will undergo dearomatising addition even into relatively electron rich rings [35][36][37][38], the

• . However, immediate hydrogenation at ambient pressure using the conditions developed by Arnott for related 3,4-fused dihydropyridines [39] gave 15 in 45% yield after chromatography as an inseparable mixture of two diastereoisomers in a ratio of approximately 6:1. A slightly improved yield of 48% was

• dihydropyridines has always led to cis stereochemistry at the ring junction [32][39]. The consequent expected axial–equatorial relationship between the protons at the ring junction is supported by a coupling constant of 4.2 Hz between these protons in 15 (Figure 1) in the major product diastereoisomer. The