Non-covalent organocatalyzed enantioselective cyclization reactions of α,β-unsaturated imines

• Sergio Torres-Oya and
• Mercedes Zurro

Beilstein J. Org. Chem. 2024, 20, 3221–3255, doi:10.3762/bjoc.20.268

• cycloadducts 29e and 31e in good yields (Scheme 12). Further derivatizations were also carried out: The treatment of 29e with SOCl2 led to interesting unsaturated derivative 32 in a 54% yield. The acetylation of 31e provided 33 in 76% yield. Next, an alkene metathesis of 33 with styrene led to product 34 in 72

Recent progress in the synthesis of homotropane alkaloids adaline, euphococcinine and N-methyleuphococcinine

• Dimas J. P. Lima,
• Antonio E. G. Santana,
• Michael A. Birkett and
• Ricardo S. Porto

Beilstein J. Org. Chem. 2021, 17, 28–41, doi:10.3762/bjoc.17.4

• approach consisted of a 3,3-sigmatropic rearrangement to give an all-carbon quaternary center, a ring-closing alkene metathesis to give an 8-membered ring, and the use of a single enantiomer of p-menthane-3-carboxaldehyde to make two natural alkaloids of opposite configuration. Firstly, (+)-euphococcinine

Catalysis of linear alkene metathesis by Grubbs-type ruthenium alkylidene complexes containing hemilabile α,α-diphenyl-(monosubstituted-pyridin-2-yl)methanolato ligands

• Tegene T. Tole,
• Johan H. L. Jordaan and
• Hermanus C. M. Vosloo

Beilstein J. Org. Chem. 2019, 15, 194–209, doi:10.3762/bjoc.15.19

• precatalysts can be attributed to electronic and steric effects associated with the adjacent bulky phenyl groups. Keywords: Grubbs-type precatalyst; hemilabile; 1-octene metathesis; pyridinyl-alcoholato ligand; Introduction The alkene metathesis reaction is now well established as a powerful synthetic tool

• (Figure 1). Of course, the role of the so-called Schrock metal carbenes based on tungsten and molybdenum should not be ignored in the success story of the alkene metathesis reaction but it is not the focus of this article. The large number of ruthenium alkylidene precatalysts that has been developed is

• alkene metathesis catalysed by ruthenium alkylidene precatalysts. The 3-OMe-substituted precatalyst 9 showed a negligible activity for the metathesis of 1-octene at 60 °C (Figure 8), similar to the 3-Me-substituted precatalyst 6. The overall activity of the precatalyst, however, showed a significant

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

• substituent (Figure 15) at the nitrogen atoms were investigated by Copéret and Thieuleux et al. in the tandem ring-opening–ring-closing alkene metathesis (RO–RCM) of cis-cyclooctene (47) and their performance were compared to those of the classical GII-SIMes and GII-IMes [29]. The dissymmetry of the NHC

The activity of indenylidene derivatives in olefin metathesis catalysts

• Maria Voccia,
• Steven P. Nolan,
• Luigi Cavallo and
• Albert Poater

Beilstein J. Org. Chem. 2018, 14, 2956–2963, doi:10.3762/bjoc.14.275

• molybdenum systems appear to confer the right environment that allows a productive alkene metathesis [10][11]. Little productive reactivity has been uncovered using other metals [12][13][14]. Apart from the metal, ruthenium-based olefin metathesis has seen several changes during the last decades, modifying

Non-metal-templated approaches to bis(borane) derivatives of macrocyclic dibridgehead diphosphines via alkene metathesis

• Tobias Fiedler,
• Michał Barbasiewicz,
• Michael Stollenz and
• John A. Gladysz

Beilstein J. Org. Chem. 2018, 14, 2354–2365, doi:10.3762/bjoc.14.211

• M in CH2Cl2) gives 6·2BH3 (5%), in,out-2·2BH3 (6%), and (in,in/out,out)-2·2BH3 (7%). Despite the doubled yield of 2·2BH3, the longer synthesis of 11·2BH3 vs 1·BH3 renders the two routes a toss-up; neither compares favorably with precious metal templated syntheses. Keywords: alkene metathesis

• evolution of synthetic strategies for dibridgehead diphosphorus compounds that employ alkene metathesis. The new approaches (Scheme 2; Scheme 3 and Scheme 5) lack metal templates, which differentiates them from the routes presented in Scheme 1. However, neither is competitive with Scheme 1, despite

• dibridgehead diphosphines derived therefrom. Synthesis and alkene metathesis of the monophosphorus precursor 1·BH3. Synthesis of the diphosphorus precursor 11·2BH3. Truncated approaches to the diphosphorus precursor 11·2BH3 from 10. Alkene metathesis of the diphosphorus precursor 11·2BH3. Schematic comparison

Computational study of productive and non-productive cycles in fluoroalkene metathesis

• Markéta Rybáčková,
• Jan Hošek,
• Ondřej Šimůnek,
• Viola Kolaříková and
• Jaroslav Kvíčala

Beilstein J. Org. Chem. 2015, 11, 2150–2157, doi:10.3762/bjoc.11.232

• . Keywords: alkene metathesis; computation; DFT; fluoroalkene; mechanism; non-productive cycle; productive cycle; Introduction Over the course of the last 20 years, alkene metathesis catalysed with homogeneous transitition metal-based precatalysts evolved into a valuable tool for organic synthetic chemists

• valuable in the study of reaction mechanisms. In particular, the use of time-efficient DFT methods for the theoretical study of alkene metathesis has been extensively reviewed [9][10][11] and computational results have been found to agree well with recent experimental mechanistic studies based on easily

• initiating ruthenium precatalysts [12][13]. A theoretical approach has been also employed in attempts to gain a better insight into the complex structure of intertwined productive and non-productive catalytic cycles of alkene metathesis [14]. In contrast to the older computations, new publications also

Olefin metathesis in air

• Lorenzo Piola,
• Fady Nahra and
• Steven P. Nolan

Beilstein J. Org. Chem. 2015, 11, 2038–2056, doi:10.3762/bjoc.11.221

• metal-catalyzed alkene metathesis [1][2][3][4][5][6][7][8][9][10], which involves a fragment exchange between alkenes, is nowadays one of the most used strategies for the formation of carbon–carbon bonds. This area of study began with a “black box” approach for catalysts formation in polymerization of

• catalyst stability but also to potentially bring operational simplicity to this now widespead assembly strategy. In this review, we summarize improvements associated with the stability of well-defined metathesis homogeneous systems towards the presence of air and water in the alkene metathesis and

• , showed the highest rate of initiation reported to date for alkene metathesis reactions. Complex 81 is used mostly for ROMP and CM reactions with electron-deficient olefins. The complex can be prepared in air but only one example of its use in air has been reported. In 2010, Tew and co-workers reported

Re₂O₇-catalyzed reaction of hemiacetals and aldehydes with O-, S-, and C-nucleophiles

• Wantanee Sittiwong,
• Michael W. Richardson,
• Charles E. Schiaffo,
• Thomas J. Fisher and
• Patrick H. Dussault

Beilstein J. Org. Chem. 2013, 9, 1526–1532, doi:10.3762/bjoc.9.174

• Brønsted or Lewis acid, or by conversion to an activated intermediate such as a haloacetal [1]. Perrhenates, best known as catalysts for large-scale alkene metathesis [2] and isomerization of allylic alcohols [3][4][5][6][7][8][9][10], have been shown to promote condensation of carbonyls with hydrogen

Recent advances in the development of alkyne metathesis catalysts

• Xian Wu and
• Matthias Tamm

Beilstein J. Org. Chem. 2011, 7, 82–93, doi:10.3762/bjoc.7.12

• ), and in analogy to Fürstner’s report [84], our studies also indicate that the addition of MS 5 Å does further improve the activity and the ease of applicability of this catalyst system. Conclusion “Although alkyne metathesis may never reach the breadth of alkene metathesis because of a smaller

Hoveyda–Grubbs type metathesis catalyst immobilized on mesoporous molecular sieves MCM-41 and SBA-15

• Hynek Balcar,
• Tushar Shinde,
• Naděžda Žilková and
• Zdeněk Bastl

Beilstein J. Org. Chem. 2011, 7, 22–28, doi:10.3762/bjoc.7.4

• molecular sieves MCM-41 and on SBA-15 by direct interaction with the sieve wall surface. The immobilized catalysts exhibited high activity and nearly 100% selectivity in several types of alkene metathesis reactions. Ru leaching was found to depend on the substrate and solvent used (the lowest leaching was

• : alkene metathesis; catalyst immobilization; hybrid catalysts; mesoporous molecular sieves; Ru–alkylidene complexes; Introduction Ru–alkylidene complexes (Grubbs and Hoveyda–Grubbs catalysts, 1 and 2, respectively, Figure 1) belong to the most active and frequently used metathesis catalysts. These

Stereoselectivity of supported alkene metathesis catalysts: a goal and a tool to characterize active sites

• Christophe Copéret

Beilstein J. Org. Chem. 2011, 7, 13–21, doi:10.3762/bjoc.7.3

• Abstract Stereoselectivity in alkene metathesis is a challenge and can be used as a tool to study active sites under working conditions. This review describes the stereochemical relevance and problems in alkene metathesis (kinetic vs. thermodynamic issues), the use of (E/Z) ratio at low conversions as a

• (styrenyl systems or alkenes with electron withdrawing substituents) [19][20][21]. Here the discussion will focus on the stereoselectivity of alkene metathesis in order to delineate the current state of the art in the case of heterogeneous catalysts and show how it can be used to characterize active sites

• as well as to put forward possible strategies to approach the problem. Review Stereoselectivity in alkene metathesis: a challenge and a tool Alkene metathesis is a reaction where the alkylidene fragments of alkenes are exchanged (transalkylidenation, Scheme 1a). The mechanism involves at least four