Diastereo- and enantioselective preparation of cyclopropanol derivatives

• Marwan Simaan and
• Ilan Marek

Beilstein J. Org. Chem. 2019, 15, 752–760, doi:10.3762/bjoc.15.71

• highly strained structure and bonding properties of cyclopropyl rings have constantly fascinated successive generations of chemists. These small carbocycles are known to have high ring strain (27.5 kcal/mol) and limited degrees of freedom, making them very attractive substrates for various chemical

Sigmatropic rearrangements of cyclopropenylcarbinol derivatives. Access to diversely substituted alkylidenecyclopropanes

• Guillaume Ernouf,
• Jean-Louis Brayer,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2019, 15, 333–350, doi:10.3762/bjoc.15.29

• the relief of ring-strain, the formation of the alkylidenecyclopropane B is generally thermodynamically favored [19][20]. However, in the particular case of gem-difluorocyclopropenes A’ (R3 = R'3 = F) which possess a cyclopropenium (aromatic) character, the position of the equilibrium depends on the

• rearrangement of 10a occurred was attributed to the relief of ring strain but also to the favorable conjugation of the olefin with the two phenyl groups (R1 = R’1 = Ph). Alkylidenecyclopropane 11a could also be obtained in similar yields (92% or 87%, respectively) by heating acetate 10a in dichloromethane at

Oxidative radical ring-opening/cyclization of cyclopropane derivatives

• Yu Liu,
• Qiao-Lin Wang,
• Zan Chen,
• Cong-Shan Zhou,
• Bi-Quan Xiong,
• Pan-Liang Zhang,
• Chang-An Yang and
• Quan Zhou

Beilstein J. Org. Chem. 2019, 15, 256–278, doi:10.3762/bjoc.15.23

• molecule with the molecular formula C3H6, consisting of three carbon atoms linked to each other to form a ring, with each carbon atom bearing two hydrogen atoms resulting in D3h molecular symmetry. The small size of the ring creates substantial ring strain in the structure. The cyclopropane skeleton easily

Ruthenium-based olefin metathesis catalysts with monodentate unsymmetrical NHC ligands

• Veronica Paradiso,
• Chiara Costabile and
• Fabia Grisi

Beilstein J. Org. Chem. 2018, 14, 3122–3149, doi:10.3762/bjoc.14.292

• , giving predominantly poly(COE). Due to its superior activity, complex 153 was also investigated in the ethenolysis of more challenging substrates such as norbornene derivatives, which typically are among the most popular ROMP monomers because of their high ring strain. The efficient synthesis of valuable

Organometallic vs organic photoredox catalysts for photocuring reactions in the visible region

• Aude-Héloise Bonardi,
• Frédéric Dumur,
• Guillaume Noirbent,
• Jacques Lalevée and
• Didier Gigmes

Beilstein J. Org. Chem. 2018, 14, 3025–3046, doi:10.3762/bjoc.14.282

• -opening metathesis polymerization. This polymerization is based on cyclic olefins whose ring strain is released during polymerization. This reaction needs a catalyst to occur [108]. Metal-free photoredox catalysts for ROMP were proposed in [109]. For example, pyrylium and acridinium salts can be used as

Dispersion-mediated steering of organic adsorbates on a precovered silicon surface

• Lisa Pecher,
• Sebastian Schmidt and
• Ralf Tonner

Beilstein J. Org. Chem. 2018, 14, 2715–2721, doi:10.3762/bjoc.14.249

• . The adsorption of a first molecule of 1 on Si(001) is characterized by a direct adsorption path without intermediate structure leading to a strongly covalently bonded [2 + 2] cycloaddition product 2 as summarized in Scheme 1 with ring strain being decisive for the high reactivity of 1 [5][6][8]. Not

Ring-opening metathesis of some strained bicyclic systems; stereocontrolled access to diolefinated saturated heterocycles with multiple stereogenic centers

• Zsanett Benke,
• Melinda Nonn,
• Márton Kardos,
• Santos Fustero and
• Loránd Kiss

Beilstein J. Org. Chem. 2018, 14, 2698–2707, doi:10.3762/bjoc.14.247

• -membered ring system thus possessing ring strain, did not afford any ROM products. Interestingly, lactone (±)-3 in the presence of second generation catalysts (G-2 and HG-2) provided the corresponding ring-opened compound (±)-5 albeit with modest yields (Scheme 3, Table 1). In the presence of G-2 and HG-2

• that unsaturated bicyclic β-lactams (±)-2 and (±)-8, bearing the fused four-membered and six-membered ring system, have a lower ring strain than bicyclic, unsaturated γ-lactones (±)-3, (±)-4 and (±)-9. Because of their higher constraint, the latter compounds underwent ring opening providing the

• corresponding monocyclic, dialkenylated amino lactones, albeit with modest yields (Scheme 5); (for relevant literature date for the ROM for various cyclic systems with ring strain see ref. [27][28][29]. We continued our ring-opening investigations with other model derivatives possessing a larger ring system

Selective formation of a zwitterion adduct and bicarbonate salt in the efficient CO₂ fixation by N-benzyl cyclic guanidine under dry and wet conditions

• Yoshiaki Yoshida,
• Naoto Aoyagi and
• Takeshi Endo

Beilstein J. Org. Chem. 2018, 14, 2204–2211, doi:10.3762/bjoc.14.194

• particular, CO2 capture–release behaviors of bicyclic and six-membered cyclic amidine derivatives have been well studied compared to that of five-membered derivatives, because the high ring strain of five-membered cyclic amidine derivatives was unfavorable for the binding between CO2 and the amidine moiety

β-Hydroxy sulfides and their syntheses

• Mokgethwa B. Marakalala,
• Edwin M. Mmutlane and
• Henok H. Kinfe

Beilstein J. Org. Chem. 2018, 14, 1668–1692, doi:10.3762/bjoc.14.143

• . Regioselective epoxide ring opening and 1,2-difunctionalization of alkenes are the commonly employed routes in the synthesis of such compounds. Both strategies are discussed below. 3.1 Synthesis of β-hydroxy sulfides via regioselective ring opening of epoxides The considerable ring strain present in epoxides

[3 + 2]-Cycloaddition reaction of sydnones with alkynes

• Veronika Hladíková,
• Jiří Váňa and
• Jiří Hanusek

Beilstein J. Org. Chem. 2018, 14, 1317–1348, doi:10.3762/bjoc.14.113

• -disubstituted pyrazoles. Unsuccessful reaction with phenylpropiolic acid. Synthetic strategy leading to 1,4,5-trisubstituted pyrazoles. Reaction of sydnones carrying in position 4- six-membered 2-N-heterocyclic ring. Strain-promoted sydnone alkyne cycloaddition (SPSAC). Synthesis of a key intermediate of

Acid-catalyzed ring-opening reactions of a cyclopropanated 3-aza-2-oxabicyclo[2.2.1]hept-5-ene with alcohols

• Katrina Tait,
• Alysia Horvath,
• Nicolas Blanchard and
• William Tam

Beilstein J. Org. Chem. 2017, 13, 2888–2894, doi:10.3762/bjoc.13.281

• unit adds ring-strain to the molecule that could lead to different pathways for ring-opening and further reactivity. While the reactivity of 3-aza-2-oxabicyclo[2.2.1]hept-5-enes has been extensively studied (Scheme 1 and Scheme 2), there are only two examples in the literature investigating the

Experimental and theoretical investigations into the stability of cyclic aminals

• Edgar Sawatzky,
• Antonios Drakopoulos,
• Martin Rölz,
• Christoph Sotriffer,
• Bernd Engels and
• Michael Decker

Beilstein J. Org. Chem. 2016, 12, 2280–2292, doi:10.3762/bjoc.12.221

• compound 8a (Table 1) suggesting a correlation of increased conformational energy of the ring system and increased sensitivity toward hydrolysis. This increase in energy might well be attributed to different geometrical effects including ring strain, strain of the angles or steric repulsion of the side

• groups. It might be possible that an increased ring strain at the nitrogens of the tetrahydroquinazoline system could increase the basicity of these compounds and therefore accelerate the induction of hydrolysis, although previous studies showed that the relationship between the magnitude of ring strain

Biosynthesis of oxygen and nitrogen-containing heterocycles in polyketides

• Franziska Hemmerling and
• Frank Hahn

Beilstein J. Org. Chem. 2016, 12, 1512–1550, doi:10.3762/bjoc.12.148

• biosynthesis and was proposed to catalyse the stereospecific oxidative radical-coupling reaction of griseophenone C (187, Scheme 26b). 1.8 Oxetanones Salinosporamide. Oxetanones are rare structures and highly reactive due to their ring strain. One of the most prominent examples is the proteasome inhibitor

Reactivity studies of pincer bis-protic N-heterocyclic carbene complexes of platinum and palladium under basic conditions

• David C. Marelius,
• Curtis E. Moore,
• Arnold L. Rheingold and
• Douglas B. Grotjahn

Beilstein J. Org. Chem. 2016, 12, 1334–1339, doi:10.3762/bjoc.12.126

• for the NM nitrogen. The ∆∆ values for both nitrogens are relatively unchanged as the carbene character of the ligand is still intact. Interestingly, 6-Pd shows a similar small ∆∆ value for the NH (2.6) but a greater ∆∆ for the NM of 17.4 ppm. This is possibly a result of the differing ring strain in

Conjugate addition–enantioselective protonation reactions

• James P. Phelan and
• Jonathan A. Ellman

Beilstein J. Org. Chem. 2016, 12, 1203–1228, doi:10.3762/bjoc.12.116

• isopropyl group and a pendent methyl ester. Generally, the azetidine nitroalkenes provided the 1,2-nitrothioacetates in higher yields and enantioselectivity (81–99% yield, 95:5 to 98:2 er). The oxetane and N-Boc azetidine nitroalkenes were activated toward conjugate addition by the release of ring-strain

The synthesis of functionalized bridged polycycles via C–H bond insertion

• Jiun-Le Shih,
• Po-An Chen and
• Jeremy A. May

Beilstein J. Org. Chem. 2016, 12, 985–999, doi:10.3762/bjoc.12.97

• insertions, and inspiration for subsequent efforts of greater complexity. The transannular C–H bond insertion by an axially disposed carbene group that is needed for bridged-ring formation occurs readily, but pathways that lead to fused products having less ring strain or that lead to dimer formation must be

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