Ring contraction and ring expansion reactions in terpenoid biosynthesis and their application to total synthesis

• Nicolas Kratena,
• Nicolas Heinzig and
• Peter Gärtner

Beilstein J. Org. Chem. 2026, 22, 289–343, doi:10.3762/bjoc.22.21

• . The ring enlargement is then proposedly initiated by protonation of the olefin giving rise to 101a, 1,2-alkyl shift to 101b and elimination to re-form the exocyclic olefin in 99. An elegant bioinspired synthesis of antroalbocin A (99) was reported by Kalesse using a photochemical rearrangement of a 5

6’-Fluoro[4.3.0]bicyclo nucleic acid: synthesis, biophysical properties and molecular dynamics simulations

• Sibylle Frei,
• Andrei Istrate and
• Christian J. Leumann

Beilstein J. Org. Chem. 2018, 14, 3088–3097, doi:10.3762/bjoc.14.288

• -ROESY experiments (Supporting Information File 1). The gem-difluorinated tricyclic nucleoside 12β was then converted into the bicyclic fluoroenone 13 via desilylation and ring-enlargement by short exposure to HF-pyridine. During the following Luche reduction of derivative 13 the benzoyl protecting group

• duplexes. Results and Discussion Synthesis of the phosphoramidite building blocks Our strategy for the construction of the two phosphoramidite building blocks 10 and 16 envisaged as a key step the formation of a [4.3.0]bicyclic fluoroenone from a tricyclic siloxydifluorocyclopropane through a ring

• enlargement via selective cyclopropane ring opening [46][47][48][49]. Consequently, the synthesis started from the previously described bicyclic silyl enol ethers 1α/β (Scheme 1) [50][51]. The two anomers of 1 were individually transformed into the trimethylsilyl (TMS)-protected sugars 2α/β by adapting and

Continuous-flow retro-Diels–Alder reaction: an efficient method for the preparation of pyrimidinone derivatives

• Imane Nekkaa,
• Márta Palkó,
• István M. Mándity and
• Ferenc Fülöp

Beilstein J. Org. Chem. 2018, 14, 318–324, doi:10.3762/bjoc.14.20

• di-exo- or di-endo-amino acids or esters with ethyl p-chlorobenzimidate resulted in tricyclic pyrimidinones 1, 2a and 2b [26][45][46][47][48][49]. Methanopyrrolo-, methanopyrido- and methanoazepino[2,1-b]quinazolinones 3–6 were prepared by ring enlargement of di-exo-norbornene-fused azetidinones with

NHC-catalyzed cleavage of vicinal diketones and triketones followed by insertion of enones and ynones

• Ken Takaki,
• Makoto Hino,
• Akira Ohno,
• Kimihiro Komeyama,
• Hiroto Yoshida and
• Hiroshi Fukuoka

Beilstein J. Org. Chem. 2017, 13, 1816–1822, doi:10.3762/bjoc.13.176

• ; N-heterocyclic carbene; ring enlargement; Stetter reaction; vicinal polyketone; Introduction N-Heterocyclic carbenes (NHCs) have been indispensable catalysts for organic synthesis, particularly for umpolung of various functional groups [1][2][3][4][5][6][7][8][9]. In the Stetter reaction, NHCs

• ring-enlargement procedure to afford cyclic 1,4-diketones IV. With respect to the active species in the Stetter reaction, aminoenols II (G = H, Breslow intermediates) had been postulated as true nucleophiles for a long time and those generated from imidazolinium NHC were recently isolated in pure form

• phenyl vinyl ketone (6a) to afford 2-benzoylcyclooctane-1,4-dione (7a) in 27% yield [15]. Since this reaction would be a unique ring enlargement by two carbons, an improvement of the reaction conditions has been tested. Although the yield increased to 45% by the use of diisopropylamine instead of DIPEA

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

• reduction, and ring enlargement. One isomeric dialkyne additionally allows for the isolation of a pentacyclic compound lacking the ring enlargement step, which we have proposed as a potential intermediate in the catalytic cycle. Keywords: alkynes; camphor derivatives; catalysis; cycloisomerisation

• the C–C bond between the atoms bearing the OH and NH groups (ring enlargement). The result is an isomerisation of 4a and 4b to form tricyclic compounds 7 containing a nine-membered carbocyclic ring (Scheme 3a) [27]. Isomerisations are the best examples for a perfect “atom economy” [28][29][30] since

• -activation process, to establish an additional bond to one of the adamantyl groups (8 in Scheme 3b) [32]. The simplest diyne 4d with R = H, in contrast, gave a ring enlargement from six to seven members together with a 1,2-oxygen shift instead (9 in Scheme 3c) [33]. This clearly demonstrates that the

Iodination of carbohydrate-derived 1,2-oxazines to enantiopure 5-iodo-3,6-dihydro-2H-1,2-oxazines and subsequent palladium-catalyzed cross-coupling reactions

• Michal Medvecký,
• Igor Linder,
• Luise Schefzig,
• Hans-Ulrich Reissig and
• Reinhold Zimmer

Beilstein J. Org. Chem. 2016, 12, 2898–2905, doi:10.3762/bjoc.12.289

• modifications and synthetic applications of 1,2-oxazines 3 including the preparation of seven-membered N,O-heterocycles by ring enlargement [5], functionalization of the enol ether unit [6][7][8][9][10][11], and N,O-cleavage reactions leading to amino alcohols [8][10][12], pyrroles [13] or α,β-unsaturated β

Selected synthetic strategies to cyclophanes

• Sambasivarao Kotha,
• Mukesh E. Shirbhate and
• Gopalkrushna T. Waghule

Beilstein J. Org. Chem. 2015, 11, 1274–1331, doi:10.3762/bjoc.11.142

Dimerisation, rhodium complex formation and rearrangements of N-heterocyclic carbenes of indazoles

• Zong Guan,
• Jan C. Namyslo,
• Martin H. H. Drafz,
• Martin Nieger and
• Andreas Schmidt

Beilstein J. Org. Chem. 2014, 10, 832–840, doi:10.3762/bjoc.10.79

• -amidate 5, and indazolium-3-thioamidate 6, respectively [23] (Scheme 2). Aliphatic ketones surprisingly give stable 1:1 adducts 7 [20][24]. α-Bromo acetophenones induce an unexpected ring enlargement to cinnolines 8 [25]. New ring systems such as 9 [25] and 10 [26] were prepared on treatment of indazol-3

Synthesis of new enantiopure poly(hydroxy)aminooxepanes as building blocks for multivalent carbohydrate mimetics

• Léa Bouché,
• Maja Kandziora and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2014, 10, 213–223, doi:10.3762/bjoc.10.17

• interesting option is the pathway via oxepines [15][16][17][18] and the subsequent dihydroxylation or direct reduction of their C=C double bond to give the corresponding oxepane derivatives [19][20]. Alternatively, oxepanes were also synthesized by the ring enlargement of their six-membered homologues [21][22

Synthesis of 2,6-disubstituted tetrahydroazulene derivatives

• Zakir Hussain,
• Henning Hopf,
• Khurshid Ayub and
• S. Holger Eichhorn

Beilstein J. Org. Chem. 2012, 8, 693–698, doi:10.3762/bjoc.8.77

• 22060, KPK, Pakistan; Fax: +92 (992) 383441 Department of Chemistry and Biochemistry, University of Windsor, 401 Sunset Avenue, Essex Hall, Windsor, ON Canada N9B 3P4, Fax: +1 (519) 973-7064 10.3762/bjoc.8.77 Abstract Synthesis of hydroazulene derivatives has been carried out through a ring-enlargement

Recent advances in the gold-catalyzed additions to C–C multiple bonds

• He Huang,
• Yu Zhou and
• Hong Liu

Beilstein J. Org. Chem. 2011, 7, 897–936, doi:10.3762/bjoc.7.103

• . reported a general gold-catalyzed direct oxidative homo-coupling of non-activated arenes 207 (Scheme 38). The reaction protocol tolerates a wide range of functional groups [92]. All halogens survive the reaction, which provides the potential for further reactions. 4.2 Rearrangements and ring enlargement A

Photoinduced homolytic C–H activation in N-(4-homoadamantyl)phthalimide

• Nikola Cindro,
• Margareta Horvat,
• Kata Mlinarić-Majerski,
• Axel G. Griesbeck and
• Nikola Basarić

Beilstein J. Org. Chem. 2011, 7, 270–277, doi:10.3762/bjoc.7.36

• of the 1,5-biradical. Minor products 7 were formed by photoinduced γ H-abstractions, followed by ring closure to azetidinols and ring enlargement to azepinediones. The observed selectivity to exo-alcohol 6 was explained by the conformation of 5 and the best orientation and the availability of the δ-H

• activity [53][54][55]. Thus, photoproducts derived from 5 may also exhibit antiviral activity, although that is yet to be substantiated. Results and Discussion The synthesis of homoadamantylphthalimide 5 started from homoadamantanone 3 which is easily prepared by the ring enlargement of adamantanone with

• gives a 1,4-biradical (1,4BR) that cyclizes to azetidinol intermediates AZT1 and AZT2. Azetidinols undergo subsequent ring enlargement to furnish products anti-7 and syn-7, respectively. The ratio of the isolated compounds 7 is 5:1. However, no assignment of their stereochemistry was made from their

Novel loop-like aromatic compounds: a further step on the road to nanobelts and nanotubes

• Venkataramana Rajuri,
• Dariush Ajami,
• Gaston R. Schaller,
• Christian Näther and
• Rainer Herges

Beilstein J. Org. Chem. 2010, 6, No. 30, doi:10.3762/bjoc.6.30

• reaction [7][8][11] and ring enlargement metathesis [12][13][14][15] of 9,9′,10,10′-tetradehydrodianthracene (TDDA) (7) [16]. In a second step we anticipated closing the tube walls by cyclodehydrogenation [17]. Results and Discussion We now report on the synthesis of five new compounds, two hydrocarbons