A modular approach to neutral P,N-ligands: synthesis and coordination chemistry

• Vladislav Vasilenko,
• Torsten Roth,
• Clemens K. Blasius,
• Sebastian N. Intorp,
• Hubert Wadepohl and
• Lutz H. Gade

Beilstein J. Org. Chem. 2016, 12, 846–853, doi:10.3762/bjoc.12.83

• –C–N angles of the formamidine unit closely resemble those found in related amidinium salts, thus indicating that no significant ring strain is present. The M−Ccod bonds located trans to the P atoms are slightly longer (av 2.11 Å) than the M−Ccod bonds trans to the imino group (av 2.04 Å), suggesting

Synthesis of Xenia diterpenoids and related metabolites isolated from marine organisms

• Tatjana Huber,
• Lara Weisheit and
• Thomas Magauer

Beilstein J. Org. Chem. 2015, 11, 2521–2539, doi:10.3762/bjoc.11.273

• -selectivity of the olefin depends on the ring-size and the choice of catalyst. As a consequence of avoiding ring strain, small- and medium-sized rings are generally obtained with Z-configuration of the alkene. The Grob fragmentation reaction of fused 6,5-bicycles B is usually a concerted process that affords

Investigation on the reactivity of α-azidochalcones with carboxylic acids: Formation of α-amido-1,3-diketones and highly substituted 2-(trifluoromethyl)oxazoles

• Kandasamy Rajaguru,
• Arumugam Mariappan,
• Rajendran Suresh,
• Periasamy Manivannan and
• Shanmugam Muthusubramanian

Beilstein J. Org. Chem. 2015, 11, 2021–2028, doi:10.3762/bjoc.11.219

• -azirines are impressive intermediates for the synthesis of various substituted heterocyclic compounds [23][24][25]. Nucleophiles can interact with the electrophilic carbon of the strained 2H-azirine rings and due to the ring strain in the three-membered 2H-azirine ring system A1, the electrophilic

Copper-catalyzed aerobic radical C–C bond cleavage of N–H ketimines

• Ya Lin Tnay,
• Gim Yean Ang and
• Shunsuke Chiba

Beilstein J. Org. Chem. 2015, 11, 1933–1943, doi:10.3762/bjoc.11.209

• , which is driven by releasing ring strain of the cyclobutyl ring. The resulting γ-keto radical J subsequently undergoes radical bromination to form 8e [59]. This result unambiguously supports the presence of the alkoxy radical intermediate during oxaspirocyclohexadienone formation in our mechanistic

Recent applications of ring-rearrangement metathesis in organic synthesis

• Sambasivarao Kotha,
• Milind Meshram,
• Priti Khedkar,
• Shaibal Banerjee and
• Deepak Deodhar

Beilstein J. Org. Chem. 2015, 11, 1833–1864, doi:10.3762/bjoc.11.199

• . However, a limited number of papers appeared dealing with RRM due to the complexity involved in designing the required precursors suitable for RRM. There are several factors which facilitates the RRM. Among them, the release of ring strain is the main driving force. For example, with bicyclo[2.2.1]heptene

• release of ring strain is a less important contributor to the driving force of the reaction. However, unfavorable interaction of vicinal or proximal substituents may be minimized in the rearranged product. In this context, Blechert and co-workers [16] demonstrated the first enantioselective total

SmI₂-mediated dimerization of indolylbutenones and synthesis of the myxobacterial natural product indiacen B

• Nils Marsch,
• Peter G. Jones and
• Thomas Lindel

Beilstein J. Org. Chem. 2015, 11, 1700–1706, doi:10.3762/bjoc.11.184

• by treatment with p-TsOH (20 mol %) in chloroform (Scheme 3). As a consequence of smaller ring strain, the double bond is formed in β,γ-position to the carbonyl group. The relative configuration of tertiary alcohol 15 was determined on the basis of NOESY correlations, which revealed that 1-H (4.58

Grubbs–Hoveyda type catalysts bearing a dicationic N-heterocyclic carbene for biphasic olefin metathesis reactions in ionic liquids

• Maximilian Koy,
• Hagen J. Altmann,
• Benjamin Autenrieth,
• Wolfgang Frey and
• Michael R. Buchmeiser

Beilstein J. Org. Chem. 2015, 11, 1632–1638, doi:10.3762/bjoc.11.178

• yield is attributed to the comparable low ring strain in M6. Polydispersity indices (PDIs) were in the range of 1.2 to 3.8. Together with the high molecular weights, this is indicative for substantial chain transfer and potentially incomplete initiation of the Ru–alkylidene, particularly with

Design and synthesis of polycyclic sulfones via Diels–Alder reaction and ring-rearrangement metathesis as key steps

• Sambasivarao Kotha and
• Rama Gunta

Beilstein J. Org. Chem. 2015, 11, 1373–1378, doi:10.3762/bjoc.11.148

• , in almost all instances the products produced are cis-configured at the ring junctions. The main driving force for the RRM of these systems is the release of ring strain. The configuration is transferred from the starting material to the product. In connection with our interest to design new

Spiro annulation of cage polycycles via Grignard reaction and ring-closing metathesis as key steps

• Sambasivarao Kotha,
• Mohammad Saifuddin,
• Rashid Ali and
• Gaddamedi Sreevani

Beilstein J. Org. Chem. 2015, 11, 1367–1372, doi:10.3762/bjoc.11.147

• are interesting targets because of their unusual structural features such as the deformation of the ideal C–C bond angles, high degree of symmetry and the enhanced ring strain etc. [5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The structures of a variety of intricate cage systems, for example

Surprisingly facile CO₂ insertion into cobalt alkoxide bonds: A theoretical investigation

• Willem K. Offermans,
• Claudia Bizzarri,
• Walter Leitner and
• Thomas E. Müller

Beilstein J. Org. Chem. 2015, 11, 1340–1351, doi:10.3762/bjoc.11.144

• molecule(s). Accompanied by high activation barriers, the ring opening of the epoxide and the electrophilic insertion into either the zinc–alkoxide or zinc carbonate bond occur consecutively. Only if the ring is pre-activated by, for example, sufficient ring strain, the polymerisation reaction does become

Design and synthesis of fused polycycles via Diels–Alder reaction and ring-rearrangement metathesis as key steps

• Sambasivarao Kotha and
• Ongolu Ravikumar

Beilstein J. Org. Chem. 2015, 11, 1259–1264, doi:10.3762/bjoc.11.140

• routes to polycycles. For successful application of this strategy it is desirable that the starting materials have ring strain so that they can readily undergo a C=C double bond cleavage. Release of ring strain is the main driving force for RRM. In this regard, bicyclo[2.2.1] and bicyclo[2.2.2] systems

Hydrogenation of unactivated enamines to tertiary amines: rhodium complexes of fluorinated phosphines give marked improvements in catalytic activity

• Sergey Tin,
• Tamara Fanjul and
• Matthew L. Clarke

Beilstein J. Org. Chem. 2015, 11, 622–627, doi:10.3762/bjoc.11.70

• to the fact that there is a ring strain due to the double bond in a 6-membered ring, which is released after the double bond is hydrogenated. 1a does not get hydrogenated with the catalysts studied. It is likely that this is due to the substrate binding to the catalyst via the pyridine nitrogen and

Total synthesis of the proposed structure of astakolactin

• Takayuki Tonoi,
• Keisuke Mameda,
• Moe Fujishiro,
• Yutaka Yoshinaga and
• Isamu Shiina

Beilstein J. Org. Chem. 2014, 10, 2421–2427, doi:10.3762/bjoc.10.252

• saturated medium-sized lactones, which are generally difficult to construct because of the ring strain and transannular interactions [27][28], can be effectively prepared [29][30]. Therefore, in order to determine the chemical structure and the expected biological activity of compound 1, we executed the

Structure/affinity studies in the bicyclo-DNA series: Synthesis and properties of oligonucleotides containing bc^en-T and iso-tricyclo-T nucleosides

• Branislav Dugovic,
• Michael Wagner and
• Christian J. Leumann

Beilstein J. Org. Chem. 2014, 10, 1840–1847, doi:10.3762/bjoc.10.194

• release of ring strain during cyclopropyl rearrangement which contributes to the stabilization of the E1 transition state. Based on these assumptions we changed the oxidant from iodine to t-BuOOH, which has successfully been used in the past in the allyloxycarbonyl base- and phosphate protecting scheme

Visible light mediated intermolecular [3 + 2] annulation of cyclopropylanilines with alkynes

• Theresa H. Nguyen,
• Soumitra Maity and
• Nan Zheng

Beilstein J. Org. Chem. 2014, 10, 975–980, doi:10.3762/bjoc.10.96

• ; visible light; Introduction Cyclopropanes have been used as a three-carbon synthon to prepare a diverse array of organic compounds [1][2][3][4]. The unusual reactivity, exhibited by cyclopropanes, is largely due to their inherent ring strain that makes cleavage of the C–C bonds facile [5]. A number of

Advancements in the mechanistic understanding of the copper-catalyzed azide–alkyne cycloaddition

• Regina Berg and
• Bernd F. Straub

Beilstein J. Org. Chem. 2013, 9, 2715–2750, doi:10.3762/bjoc.9.308

Bidirectional cross metathesis and ring-closing metathesis/ring opening of a C₂-symmetric building block: a strategy for the synthesis of decanolide natural products

• Bernd Schmidt and
• Oliver Kunz

Beilstein J. Org. Chem. 2013, 9, 2544–2555, doi:10.3762/bjoc.9.289

• the build-up of ring strain. We started this investigation with the simple derivative 33, which was synthesized from 30 [60] via a sequence of three steps. For the macrolactonization of 33 we chose Yamaguchi’s method, but applied significantly more forcing conditions by using increased amounts of

The chemistry of amine radical cations produced by visible light photoredox catalysis

• Jie Hu,
• Jiang Wang,
• Theresa H. Nguyen and
• Nan Zheng

Beilstein J. Org. Chem. 2013, 9, 1977–2001, doi:10.3762/bjoc.9.234

• initialize radical polymerization of HEA. Because of ring strain, cyclopropanes are prone to ring opening via cleavage of one of the three C–C bonds. The resulting reactive intermediates have been shown to participate in a number of synthetic/mechanistic applications [103][104]. One of these applications is

• ring opening to release the ring strain while producing a distonic ion 149 with a primary radical. Distonic ion 149 is added via a Giese-type radical addition to an alkene, yielding a more stable distonic ion 151 with a secondary radical. Intramolecular addition of the secondary radical to the iminium

Gold-catalyzed reaction of oxabicyclic alkenes with electron-deficient terminal alkynes to produce acrylate derivatives

• Yin-wei Sun,
• Qin Xu and
• Min Shi

Beilstein J. Org. Chem. 2013, 9, 1969–1976, doi:10.3762/bjoc.9.233

• these previous findings, we envisaged that oxabicyclic alkenes could also react with electron-deficient alkynes in the presence of gold catalysts to generate a new C–C or C–O bond thereby releasing the oxabicyclic alkenes of their ring strain. In this paper, we report the formation of (Z)-acrylate

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

Beilstein J. Org. Chem. 2012, 8, 1936–1998, doi:10.3762/bjoc.8.225

The preferred conformation of erythro- and threo-1,2-difluorocyclododecanes

• Yi Wang,
• Peer Kirsch,
• Tomas Lebl,
• Alexandra M. Z. Slawin and
• David O'Hagan

Beilstein J. Org. Chem. 2012, 8, 1271–1278, doi:10.3762/bjoc.8.143

• NMR study. For the erythro stereoisomer 5a, three conformers I–III were considered. Conformers I and II each have a fluorine pointing into the ring (endo), and thus there is an increase in transannular ring strain, raising the energy of these conformers by 2.81 and 3.72 kcal·mol−1 respectively above

Synthesis of a library of tricyclic azepinoisoindolinones

• Bettina Miller,
• Shuli Mao,
• Kara M. George Rosenker,
• Joshua G. Pierce and
• Peter Wipf

Beilstein J. Org. Chem. 2012, 8, 1091–1097, doi:10.3762/bjoc.8.120

• instead of 4 under the metathesis conditions could be explained by a ruthenium-catalyzed double-bond isomerization [32]. The release of ring strain, however, can only be partially responsible for this facile isomerization. DFT calculations of the five possible alkene isomers of 4 indicated a decrease in

Control over molecular motion using the cis–trans photoisomerization of the azo group

• Estíbaliz Merino and
• María Ribagorda

Beilstein J. Org. Chem. 2012, 8, 1071–1090, doi:10.3762/bjoc.8.119

• . The isomers (trans,trans) and (cis,cis) are 28 and 2.6 kcal∙mol−1 more stable than the intermediate isomer, respectively. The large energy difference between (trans,trans) and (trans,cis) isomers indicates the ring strain that exists in the (trans,cis) isomer, and the thermal isomerization from (cis

Expanding the chemical diversity of spirooxindoles via alkylative pyridine dearomatization

• Chunhui Dai,
• Bo Liang and
• Corey R. J. Stephenson

Beilstein J. Org. Chem. 2012, 8, 986–993, doi:10.3762/bjoc.8.111

• (Table 1, entry 6), in contrast to 5-phenyl-1,3-cyclohexanedione (5c), which gave a slightly lower yield (Table 1, entry 7). Interestingly, nonequivalent 1,3-dicarbonyl compound 5d afforded single constitutional isomer (Table 1, entry 8), presumably due to the increased sterics and overall ring strain

High-affinity multivalent wheat germ agglutinin ligands by one-pot click reaction

• Henning S. G. Beckmann,
• Heiko M. Möller and
• Valentin Wittmann

Beilstein J. Org. Chem. 2012, 8, 819–826, doi:10.3762/bjoc.8.91

• GlcNAc residues kept in their optimal positions. Our molecular modeling studies revealed that the para-disubstituted aromatic linker of C3 cannot adopt a low-energy conformation if the chitobiose residues are kept in their ideal positions in the binding sites of WGA, resulting in significant ring strain

• of the triazole moieties as well as the central phenyl ring. This ring strain can be reduced by slightly pulling the GlcNAc residues directly attached to the linker out of the binding site, but at the expense of a less efficient multivalent binding of the two chitobiose entities. The chitobiose