Towards stereochemical control: A short formal enantioselective total synthesis of pumiliotoxins 251D and 237A

• Jie Zhang,
• Hong-Kui Zhang and
• Pei-Qiang Huang

Beilstein J. Org. Chem. 2013, 9, 2358–2366, doi:10.3762/bjoc.9.271

• previous assumption outlined in Scheme 4. To remove the PMB protecting group, compound 11 was treated with ammonium cerium nitrate (CAN) in CH3CN/H2O (v/v 3:1) [50] at room temperature for 4 h to afford the deprotected lactam 22 in 56% yield. Our next task was the oxidative cyclization of the olefin 22 to

Silica sulfuric acid: a reusable solid catalyst for one pot synthesis of densely substituted pyrrole-fused isocoumarins under solvent-free conditions

• Sudipta Pathak,
• Kamalesh Debnath and
• Animesh Pramanik

Beilstein J. Org. Chem. 2013, 9, 2344–2353, doi:10.3762/bjoc.9.269

• -catalyzed oxidative lactonization or an intramolecular cyclization reaction of δ-ketoaldehydes [12], a ruthenium-catalyzed aerobic oxidative cyclization of aromatic acids with alkynes [13], an FeCl3-promoted regioselective annulation of o-(1-alkynyl)benzoates with disulfides [14], a Heck–Matsuda cyclization

Cyclopamine analogs bearing exocyclic methylenes are highly potent and acid-stable inhibitors of hedgehog signaling

• Johann Moschner,
• Anna Chentsova,
• Nicole Eilert,
• Irene Rovardi,
• Philipp Heretsch and
• Athanassios Giannis

Beilstein J. Org. Chem. 2013, 9, 2328–2335, doi:10.3762/bjoc.9.267

• , 0 °C, 93%), (2) hydroboration/oxidation (9-BBN, THF, 70 °C; then NaBO3, H2O, 50 °C, 91%) and finally, (3) oxidative cyclization (BAIB, cat. TEMPO, CH2Cl2, 25 °C, 73%) was employed. Deprotection of the silyl ether (HF, MeCN, 25 °C, 87%) and base-induced rearrangement of the steroid skeleton via the

Anodic coupling of carboxylic acids to electron-rich double bonds: A surprising non-Kolbe pathway to lactones

• Robert J. Perkins,
• Hai-Chao Xu,
• John M. Campbell and
• Kevin D. Moeller

Beilstein J. Org. Chem. 2013, 9, 1630–1636, doi:10.3762/bjoc.9.186

• have the olefin functionalized with an alcohol and a methoxy group indicating that the initial oxidative cyclization had occurred. In this case, the slightly higher oxidation potential measured for the substrate (+0.71 V versus Ag/AgCl) is consistent with a slightly slower cyclization reaction

• . Attempts to generate seven-membered ring products using the oxidative cyclization were not successful. While 30% of a methoxide opened product 16c could be obtained with lithium methoxide as the base, no cyclic product was observed when 2,6-lutidine was employed. The reactions were quite messy and

Mechanistic studies on the CAN-mediated intramolecular cyclization of δ-aryl-β-dicarbonyl compounds

• Brian M. Casey,
• Dhandapani V. Sadasivam and
• Robert A. Flowers II

Beilstein J. Org. Chem. 2013, 9, 1472–1479, doi:10.3762/bjoc.9.167

• greater stabilization of the intermediate cyclohexadienyl radical [19]. The oxidative cyclization of δ-aryl-β-dicarbonyl substrates should proceed through a similar intermediate. As a result, the same rationale can be applied here. While MacMillan and Houk performed detailed computational studies to

• that oxidative cyclization occurs only for the methoxy substrate substituted at the meta position. Overall the DFT calculations show that the origin of the reactivity as well as the selectivity in these reactions depends on the stability of the product cyclohexadienyl radical, which is reflected in the

Total synthesis of ochnaflavone

• Monica M. Ndoile and
• Fanie R. van Heerden

Beilstein J. Org. Chem. 2013, 9, 1346–1351, doi:10.3762/bjoc.9.152

• the oxidative cyclization to form ochnaflavone were established. Keywords: biflavone; diaryl ether; natural products; nucleophilic aromatic substitution; ochnaflavone; tetrahydroochnaflavone; Introduction Biflavonoids are a class of compounds that are receiving increasing attention because of their

• basic conditions (KOH) in EtOH proceeded smoothly to furnish dimeric chalcone 6, which was obtained as a yellow powder. The cyclization of 6 into the corresponding biflavone 7 was initially attempted by using a catalytic amount of iodine in DMSO at 130–140 °C, conditions often used for the oxidative

• cyclization of chalcones to flavones [25]. However, at this temperature, the reaction resulted in decomposition of the starting material. The reaction was repeated under microwave conditions as described by Menezes et al. [26] to decrease the time in which 6 was exposed to a high temperature, but

Hydrophobic analogues of rhodamine B and rhodamine 101: potent fluorescent probes of mitochondria in living C. elegans

• Laurie F. Mottram,
• Safiyyah Forbes,
• Brian D. Ackley and
• Blake R. Peterson

Beilstein J. Org. Chem. 2012, 8, 2156–2165, doi:10.3762/bjoc.8.243

• the corresponding dialkyaminophenol with o-tolualdehyde (12) [39]. Oxidative cyclization of triarylmethanes with the quinone oxidant chloranil provided 9 and 10 in modest yield. 8-Hydroxyjulolidine (14) for synthesis of HR101 10 was either purchased commercially or prepared as previously described [40

Palladium-catalyzed dual C–H or N–H functionalization of unfunctionalized indole derivatives with alkenes and arenes

• Gianluigi Broggini,
• Egle M. Beccalli,
• Andrea Fasana and
• Silvia Gazzola

Beilstein J. Org. Chem. 2012, 8, 1730–1746, doi:10.3762/bjoc.8.198

• as the sole oxidant. Among the various pyridine ligands and solvents tested to optimize the conditions, 3-carbethoxypyridine in a polar solvent (i.e., tert-amyl alcohol/AcOH in 4:1 ratio) was proven to be the most effective in providing satisfactory yields. The oxidative cyclization led also to a new

Ugi post-condensation copper-triggered oxidative cascade towards pyrazoles

• Aurélie Dos Santos,
• Laurent El Kaim,
• Laurence Grimaud and
• Caroline Ronsseray

Beilstein J. Org. Chem. 2011, 7, 1310–1314, doi:10.3762/bjoc.7.153

• . The first attempted oxidative cyclization of 2a was made with one equivalent of copper acetate in acetic acid as solvent and gave the expected pyrazolidinone 3a in a 57% isolated yield (Scheme 2, condition A). Based on our previous study, the yield was improved to reach 84% with a mixture of acetic

• uptake of oxygen helps to control the selective oxidation process. Reactions performed under air were faster but led to intractable mixtures. Analogous hydrazones prepared from pyruvic acid and benzoylformic acid with hydrazine derivatives were tested in this Ugi/oxidative cyclization sequence under

• procedure for the oxidative cyclization: N-tert-butyl-2-(6a-methyl-3,6-dioxo-2-phenylhexahydropyrrolo[3,4-c]pyrazol-5(1H)-yl)acetamide (3a): To a solution of hydrazone 2a (100 mg, 0.3 mmol) in a 10/70/20 DMF/CH3COOH/H2O mixture (0.06 M) was added Cu(OAc)2 (20 mol %). The resulting mixture was heated at 80

Combined directed ortho-zincation and palladium-catalyzed strategies: Synthesis of 4,n-dimethoxy-substituted benzo[b]furans

• Verónica Guilarte,
• M. Pilar Castroviejo,
• Estela Álvarez and
• Roberto Sanz

Beilstein J. Org. Chem. 2011, 7, 1255–1260, doi:10.3762/bjoc.7.146

• ring system, the cyclodehydration of α-aryloxy ketones [29], the Claisen rearrangement of an allyl aryl ether followed by Pd-catalyzed intramolecular oxidative cyclization [30], and the tandem Sonogashira coupling/heterocyclization of 2-halophenols with terminal alkynes [31], are some of the most used

Synthesis of cross-conjugated trienes by rhodium-catalyzed dimerization of monosubstituted allenes

• Tomoya Miura,
• Tsuneaki Biyajima,
• Takeharu Toyoshima and
• Masahiro Murakami

Beilstein J. Org. Chem. 2011, 7, 578–581, doi:10.3762/bjoc.7.67

• , entries 7 and 8). We propose that the dimerization reaction proceeds through the pathway outlined in Scheme 2. Initially, two molecules of 1a coordinate to a rhodium(I) center at the terminal carbon–carbon double bonds from their sterically less-hindered sides. Oxidative cyclization occurs in a head-to

• yields 3a together with the catalytically active rhodium(I) complex. It is also conceivable, however, that oxidative cyclization of two molecules of 1a occurs in a tail-to-tail manner to directly furnish B. The other isomer 2a could be formed through allylic 1,3-migration of rhodium from C and subsequent

Oxidative cyclization of alkenols with Oxone using a miniflow reactor

• Yoichi M. A. Yamada,
• Kaoru Torii and
• Yasuhiro Uozumi

Beilstein J. Org. Chem. 2009, 5, No. 18, doi:10.3762/bjoc.5.18

• Yoichi M. A. Yamada Kaoru Torii Yasuhiro Uozumi RIKEN, Hirosawa, Wako, Saitama 351-0198, Japan Institute for Molecular Science (IMS), Myodaiji, Okazaki, Aichi 444-8787, Japan 10.3762/bjoc.5.18 Abstract A miniflow system for oxidative cyclization of alkenols with Oxone was developed. Thus, the

• oxidative cyclization of (Z)- and (E)-alkenols in i-PrOH with an aqueous solution of Oxone proceeded smoothly and safely in a PTFE tube without any exogenous catalytic species, and was subsequently quenched in a flow-reaction manner to afford the corresponding furanyl and pyranyl carbinols quantitatively

• within 5 or 10 min of residence time. Keywords: alkenols; cyclic ethers; miniflow reaction; oxidative cyclization; Oxone; Introduction The development of flow-reaction systems for molecular transformations is an important goal in organic syntheses. Recently, innovative devices such as micro- and

Recent progress on the total synthesis of acetogenins from Annonaceae

• Nianguang Li,
• Zhihao Shi,
• Yuping Tang,
• Jianwei Chen and
• Xiang Li

Beilstein J. Org. Chem. 2008, 4, No. 48, doi:10.3762/bjoc.4.48

• diastereomers, it was suggested that the absolute configuration of natural cis-solamin was 71a. In 2002, Brown’s group [43] also reported the synthesis of cis-solamin (71a) and its diastereomer 71b using the diastereoselective permanganate-promoted oxidative cyclization of 1,5-dienes to create the THF diol core

• (Scheme 11). Notably, no protecting groups were required during the stages of fragment assembly. The synthesis of precursor 78 for the oxidative cyclization reaction was completed by hydrolysis of 77 and activation of the resulting unsaturated acid as the acid chloride followed by reaction with lithiated

• (2S)-10,2-camphorsultam. The key oxidative cyclization reaction, conducted under phase-transfer conditions, introduced the C15, C16, C19, and C20 stereocenters present in cis-solamin in one step, then the auxiliary was best removed from 79 by reduction using NaBH4. The resulting diol was taken forward