Recent advances in hypervalent iodine(III)-catalyzed functionalization of alkenes

• Xiang Li,
• Pinhong Chen and
• Guosheng Liu

Beilstein J. Org. Chem. 2018, 14, 1813–1825, doi:10.3762/bjoc.14.154

• enantioselectivity (52 vs 53). Moreover, the more electron-deficient 3,4,5-trifluorophenyl analog 54 was found to be less enantioselective. The authors proposed that the benzylic groups can stabilize the cationic intermediates and/or transition states through cation–π interactions, which play an important role in

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

Ring-size-selective construction of fluorine-containing carbocycles via intramolecular iodoarylation of 1,1-difluoro-1-alkenes

• Takeshi Fujita,
• Ryo Kinoshita,
• Tsuyoshi Takanohashi,
• Naoto Suzuki and
• Junji Ichikawa

Beilstein J. Org. Chem. 2017, 13, 2682–2689, doi:10.3762/bjoc.13.266

• cyclization. Three-membered iodonium intermediates generated in the reaction course were expected to exhibit switchable regioselectivities [22]. This is because their cationic charge might be less localized on the carbon atoms α to the fluorine substituents, as compared to the aforementioned cationic

• intermediates [23][24][25][26][27]. Thus, we examined and eventually achieved complete control over the regioselectivity at the carbon atoms in β-position as well as those in α-position to the fluorine in the intramolecular Friedel–Crafts-type iodoarylation of 1,1-difluoro-1-alkenes bearing a biaryl group

Synthesis of alkynyl-substituted camphor derivatives and their use in the preparation of paclitaxel-related compounds

• M. Fernanda N. N. Carvalho,
• Rudolf Herrmann and
• Gabriele Wagner

Beilstein J. Org. Chem. 2017, 13, 1230–1238, doi:10.3762/bjoc.13.122

• , to give a cyclic sulfinamide 6 (Scheme 2b) [26]. In this case, the mechanism of the reaction proceeded through cationic intermediates as evidenced by in situ NMR spectroscopy. Catalysis by Pt(II) can drive the reaction even further: besides annulation and sulphur reduction, one finds a cleavage of

A detailed view on 1,8-cineol biosynthesis by Streptomyces clavuligerus

• Jan Rinkel,
• Patrick Rabe,
• Laura zur Horst and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2016, 12, 2317–2324, doi:10.3762/bjoc.12.225

• a RY dimer [9]. The substrate is ionised by diphosphate abstraction and the resulting allyl cation undergoes a domino reaction via a series of cationic intermediates and a final deprotonation or attack of water to yield a terpene hydrocarbon or alcohol. This reaction cascade proceeds in a

• involved in the stabilisation of cationic intermediates, e.g., by cation–π interactions [8][9][10]. The overall process usually generates an enantiomerically pure (poly)cyclic terpene with several stereogenic centres. A large variety of carbon skeletons is accessible, e g., more than 120 skeletons each

Enantioselective additions of copper acetylides to cyclic iminium and oxocarbenium ions

• Jixin Liu,
• Srimoyee Dasgupta and
• Mary P. Watson

Beilstein J. Org. Chem. 2015, 11, 2696–2706, doi:10.3762/bjoc.11.290

• required to develop this class of reactions. In particular, all cyclic iminium and oxocarbenium ions utilized to date have been limited to those that form stabilized cationic intermediates (benzylic or aromatic). With few exceptions, the vast majority lack β-hydrogens, so competitive elimination reactions

Recent advances in the electrochemical construction of heterocycles

• Robert Francke

Beilstein J. Org. Chem. 2014, 10, 2858–2873, doi:10.3762/bjoc.10.303

• mediating system that is based on the ArS(ArSSAr)+ species, an equivalent of ArS+ (Scheme 13). ArS(ArSSAr)+ is formed upon anodic oxidation of ArSSAr at low temperatures and can be employed for the generation of cationic intermediates (indirect cation pool method) [57]. In the presence of a substrate with a

Gold-catalyzed cyclization of allenyl acetal derivatives

• Dhananjayan Vasu,
• Samir Kundlik Pawar and
• Rai-Shung Liu

Beilstein J. Org. Chem. 2013, 9, 1751–1756, doi:10.3762/bjoc.9.202

• deuterium labeling experiments supports a 1,4-hydride shift of the resulting allyl cationic intermediates because a complete deuterium transfer is observed. We tested the reaction on various acetal substrates bearing a propargyl acetate, giving 4-methoxy-5-alkylidenecyclopent-2-en-1-ones 4 via a degradation

• ]. We postulate that compounds 2 arise from the attack of 1,3-diones at initially generated allyl cation intermediates I. In the case of electrophilic nitrones, allyl cations I release a proton to form reactive 1-methoxyfulvenes II to achieve a [3 + 2]-nitrone cycloaddition. The versatility of cationic

• intermediates I encourages us to understand their behavior in the absence of a dipolarophile. This work reports gold-catalyzed intramolecular cyclizations of these allenyl acetals [19]. Results and Discussion We first tested the intramolecular cyclizations of allenyl acetal 1a with PPh3AuCl/AgSbF6 (5 mol

Recent developments in gold-catalyzed cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2011, 7, 1075–1094, doi:10.3762/bjoc.7.124

• allenes through cationic intermediates [91][92][93][94], we investigated the possibility of using allenes as allyl cation surrogates, such that they could participate in concerted [4C(4π) + 3C(2π)] cycloadditions with conjugated dienes, a similar process to those previously reported between oxyallyl

When gold can do what iodine cannot do: A critical comparison

• Sara Hummel and
• Stefan F. Kirsch

Beilstein J. Org. Chem. 2011, 7, 847–859, doi:10.3762/bjoc.7.97

• that, in some cases, gold-catalyzed domino processes can be paralleled by employing iodine electrophiles. In particular, if classical cationic intermediates are assumed to explain the gold-catalyzed reactivity of a substrate, it is reasonable to expect analogous reactivity for this substrate in the

• analogous manner either by using gold-catalysts or electrophilic iodine sources. Typically, these processes are easily understood by postulating stabilized cationic intermediates. For example, aromatic 1,5-enynes can be cyclized to the corresponding naphthalenes in the presence of gold(I) catalysts as

• stabilizing substituent at C2 were found to undergo a cascade consisting of 6-endo cyclization and a subsequent pinacol-type shift [37][98]. Since the 5-endo cyclizations discussed above most likely proceed through cationic intermediates, external nucleophiles were shown to trap these intermediates at C1 in

When cyclopropenes meet gold catalysts

• Frédéric Miege,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2011, 7, 717–734, doi:10.3762/bjoc.7.82

• nucleophilic addition with, e.g., alcohols, arenes or carbonyl groups, undergo self- or cross-carbene couplings and bring about the cyclopropanation of olefins. The first of these reaction types is often considered to be representative of cationic intermediates whereas the other two are best ascribed to