Organocatalytic cascade aza-Michael/hemiacetal reaction between disubstituted hydrazines and α,β-unsaturated aldehydes: Highly diastereo- and enantioselective synthesis of pyrazolidine derivatives

• Zhi-Cong Geng,
• Jian Chen,
• Ning Li,
• Xiao-Fei Huang,
• Yong Zhang,
• Ya-Wen Zhang and
• Xing-Wang Wang

Beilstein J. Org. Chem. 2012, 8, 1710–1720, doi:10.3762/bjoc.8.195

• stereoselective cascade reaction for the synthesis of the pyrazolidine compounds through organocatalysis. In this paper, we present a convenient access to racemic and enantioenriched 5-hydroxypyrazolidines through a domino aza-Michael/hemiacetal organocatalytic sequence of disubstituted hydrazines to α,β

• pyrazolidine derivatives through the cascade aza-Michael/hemiacetal reaction between disubstituted hydrazines and α,β-unsaturated aldehydes. The asymmetric version of this one-pot cascade reaction has also been realized with (S)-diphenylprolinol trimethylsilyl ether 1m as a secondary amine organocatalyst, and

Organocatalytic tandem Michael addition reactions: A powerful access to the enantioselective synthesis of functionalized chromenes, thiochromenes and 1,2-dihydroquinolines

• Chittaranjan Bhanja,
• Satyaban Jena,
• Sabita Nayak and
• Seetaram Mohapatra

Beilstein J. Org. Chem. 2012, 8, 1668–1694, doi:10.3762/bjoc.8.191

• acyclic α,β-unsaturated compounds In the previously reported organocatalytic tandem oxa-Michael–aldol reactions, the instantaneous dehydration of the β-hydroxyaldimine intermediates generates products with only one stereogenic center. Hong et al. [52] in 2009 reported a novel quadruple-cascade reaction

• cascade reaction starts in an analogous manner to that previously mentioned, although the first oxa-Michael step is followed by a second Michael addition to form the chroman unit. A series of α,β-unsaturated aldehydes were reacted with the o-hydroxy-β-nitrostyrene as shown in Scheme 11. Except for the

• quadruple-cascade reaction exemplifies an efficient three-component reaction. In 2010 Wang et al. [11] reported the highly enantioselective synthesis of trisubstituted chiral 4H-chromenes 20 through iminium-allenamide catalysis. The reaction consists of a Michael–Michael-cascade sequence between alkynals 5

Organocatalytic C–H activation reactions

• Subhas Chandra Pan

Beilstein J. Org. Chem. 2012, 8, 1374–1384, doi:10.3762/bjoc.8.159

• -annulation cascade reaction with N,N-(dialkylamino)benzaldehydes, a process in which a 1,5-hydride shift occurs followed by larger ring formation [16]. After the evaluation of different Brønsted acid catalysts, diphenylphosphate (20 mol %) was identified as a suitable catalyst for the reaction. Toluene again

• more organocatalytic non-asymmetric and asymmetric sp3 C–H activation processes are expected [37]. Triflic acid-catalysed synthesis of cyclic aminals. PTSA-catalysed synthesis of cyclic aminals. Plausible mechanism for cyclic aminal synthesis. Annulation cascade reaction with double nucleophiles

• . Mechanism for the indole-annulation cascade reaction. Synthesis of N-alkylpyrroles and δ-hydroxypyrroles. Synthesis of N-alkylindoles 9 and N-alkylindolines 10. Mechanistic study for the N-alkylpyrrole formation. Benzoic acid catalysed decarboxylative redox amination. Organocatalytic redox reaction of ortho

Chemistry of polyhalogenated nitrobutadienes, 10: Synthesis of highly functionalized heterocycles with a rigid 6-amino-3-azabicyclo[3.1.0]hexane moiety

• Viktor A. Zapol’skii,
• Jan C. Namyslo,
• Armin de Meijere and
• Dieter E. Kaufmann

Beilstein J. Org. Chem. 2012, 8, 621–628, doi:10.3762/bjoc.8.69

• 75–90% yield (Scheme 6). A conceivable mechanism for the cascade reaction that leads to the pyrazoles 27 and 28 is presented in Scheme 7. Initially, the trichlorobutene I is formed upon addition of the arylhydrazine to the nitro-substituted butadiene 25. Subsequent elimination of benzotriazole

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

• /aromatic amines, ethyl propiolate and benzaldehyde [14], or by a cascade reaction of 1-phenylpropynone or ethyl propiolate with primary amines and aldehyde [15]. Enaminones are versatile starting materials for the synthesis of many classes of organic compounds and heterocyclic systems [16][17], and are

Synthesis of fused tricyclic amines unsubstituted at the ring-junction positions by a cascade condensation, cyclization, cycloaddition then decarbonylation strategy

• Iain Coldham,
• Adam J. M. Burrell,
• Hélène D. S. Guerrand,
• Luke Watson,
• Nathaniel G. Martin and
• Niall Oram

Beilstein J. Org. Chem. 2012, 8, 107–111, doi:10.3762/bjoc.8.11

• ; dipolar cycloaddition; heterocycle; tricyclic; Introduction Cascade reaction sequences [1] provide a rapid and efficient means to build complexity in organic chemistry. One such sequence involves a cyclization followed by in situ intramolecular cycloaddition to give three new rings in a single

Amines as key building blocks in Pd-assisted multicomponent processes

• Didier Bouyssi,
• Nuno Monteiro and
• Geneviève Balme

Beilstein J. Org. Chem. 2011, 7, 1387–1406, doi:10.3762/bjoc.7.163

• , giving good to excellent yields (Scheme 10) [9]. Barluenga and coworkers reported a synthesis of spiroacetals 22, through a Pd(II)-catalyzed three-component cascade reaction, starting from an alkynol, an aldehyde and a primary amine. The authors suggested that the first step of the reaction was the

• basic media. A subsequent Pd-mediated intermolecular alkylation with the dihalogeno substrate followed by an intramolecular N-arylation furnished 2-substituted indoles 68. In this cascade reaction, the palladium catalyst intervenes in three different coupling reactions: Intermolecular N-alkenylation, C

Efficient gold(I)/silver(I)-cocatalyzed cascade intermolecular N-Michael addition/intramolecular hydroalkylation of unactivated alkenes with α-ketones

• Ya-Ping Xiao,
• Xin-Yuan Liu and
• Chi-Ming Che

Beilstein J. Org. Chem. 2011, 7, 1100–1107, doi:10.3762/bjoc.7.126

• molecules. Disappointingly, no conversion was observed when (t-Bu)2(o-diphenyl)PAuOTf only was used as the catalyst. Since dual-metal-catalysis is of interest from the perspective of unique reactivity [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40], we explored a new cascade reaction involving

• mixture did not have a noticeable effect on the yield of 3a (Table 1, entries 8–11). To identify further the optimal reaction conditions for the gold(I)/silver(I)-cocatalyzed cascade reaction, a number of dual-metal catalyst systems, composed of 15 mol % of silver salt with 5 mol % of gold(I) complex in

• activity and diastereo-induction in this cascade reaction (Table 2, entries 5–9). Among the complexes examined, (t-Bu)2(o-biphenyl)PAuCl gave the best result (Table 2, entry 5). Further screening of solvents revealed that toluene gave the best result, while the other solvents, dioxane, nitromethane, 1,2

Recent advances in the gold-catalyzed additions to C–C multiple bonds

• He Huang,
• Yu Zhou and
• Hong Liu

Beilstein J. Org. Chem. 2011, 7, 897–936, doi:10.3762/bjoc.7.103

• substituted naphthalenes 296 [151]. This cascade reaction involves a tandem sequence of 1,3- and 1,2-migration of two different migrating groups. Jin and Yamamoto prepared the fused tri- and tetracyclic enones 298 through an efficient gold(III)-catalyzed tandem reaction, heteroenyne metathesis, and Nazarov

• the tosylate followed by the interaction with the imine and a Nazarov-like cyclization. Barluenga et al. reported a gold-catalyzed cascade reaction involving an unusual intramolecular redox process in which 5-heteroaryl-substituted ketone derivatives 372 were obtained from secondary 5-hexyn-1-ols 370

• a highly enantioselective three-component (393–395) cascade reaction which involved an enantioselective [4 + 2] cycloaddition reaction catalyzed by a chiral phosphoric acid and a subsequent catalytic intramolecular hydroamination by a gold(I) complex (Scheme 64) [180]. Further studies revealed that

Nano copper oxide catalyzed synthesis of symmetrical diaryl sulfides under ligand free conditions

• K. Harsha Vardhan Reddy,
• V. Prakash Reddy,
• A. Ashwan Kumar,
• G. Kranthi and
• Y.V.D. Nageswar

Beilstein J. Org. Chem. 2011, 7, 886–891, doi:10.3762/bjoc.7.101

• 1, 2 and 3). Conclusion We have developed a CuO nanoparticles catalyzed synthesis of symmetrical diaryl sulfides via cascade reaction of aryl halides with potassium thiocyanate under ligand free conditions. The reaction avoids foul smelling thiols and the catalyst is economical, air stable

Synthetic applications of gold-catalyzed ring expansions

• David Garayalde and
• Cristina Nevado

Beilstein J. Org. Chem. 2011, 7, 767–780, doi:10.3762/bjoc.7.87

• nucleophilic oxidant in this context [40]. The gold-catalyzed intramolecular nucleophilic attack of heteroatoms on alkynes, followed by ring expansion, represents an appropriate method for the synthesis of furans and pyrroles. In 2006, Schmalz and co-workers reported a gold-catalyzed cascade reaction of

Construction of cyclic enones via gold-catalyzed oxygen transfer reactions

• Leping Liu,
• Bo Xu and
• Gerald B. Hammond

Beilstein J. Org. Chem. 2011, 7, 606–614, doi:10.3762/bjoc.7.71

• and the final product 4. The isolated intermediate 5 could be transformed into a mixture of 6 and 4 under the reaction conditions, finally yielding 4 via intramolecular aldol condensation. This gold-catalyzed cyclization of alkynyl ketones to enones was successfully utilized in a cascade reaction by

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

Beilstein J. Org. Chem. 2009, 5, No. 33, doi:10.3762/bjoc.5.33

Reversible intramolecular photocycloaddition of a bis(9-anthrylbutadienyl)paracyclophane – an inverse photochromic system. (Photoactive cyclophanes 5)

• Henning Hopf,
• Christian Beck,
• Jean-Pierre Desvergne,
• Henri Bouas-Laurent,
• Peter G. Jones and
• Ludger Ernst

Beilstein J. Org. Chem. 2009, 5, No. 20, doi:10.3762/bjoc.5.20

• to dibenzoequinine, a stable polycyclic molecule [27]. In that case, the first Diels-Alder addition is immediately followed by a second, because of the superimposition of the newly formed diene and the ene centres (cascade reaction). This is not possible in the present situation, considering Figure