Fused bicyclic piperidines and dihydropyridines by dearomatising cyclisation of the enolates of nicotinyl-substituted esters and ketones

• Heloise Brice,
• Jonathan Clayden and
• Stuart D. Hamilton

Beilstein J. Org. Chem. 2010, 6, No. 22, doi:10.3762/bjoc.6.22

• Heloise Brice Jonathan Clayden Stuart D. Hamilton School of Chemistry, University of Manchester, Oxford Rd., Manchester M13 9PL, United Kingdom 10.3762/bjoc.6.22 Abstract The silyl enol ether derivatives of ketones or esters tethered by a hydrocarbon or ether linkage to the 3-position of a

• : bicyclic; cyclisation; dearomatisation; enol ether; heterocycle; pyridine; quinoline; Introduction Oxidative [1][2][3] or reductive (nucleophilic) [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] dearomatising cyclisation reactions are effective strategies for rapidly building complexity

• it into a silyl enol ether 9. Silyl enol ethers and ketene acetals are known to add effectively to pyridinium species in an intermolecular manner [42][43][44][45][46]. Thus 7 was converted to silyl enol ether 9 in excellent yield under standard conditions. A single geometrical isomer was obtained

Synthesis of lipophilic 1-deoxygalactonojirimycin derivatives as D-galactosidase inhibitors

• Georg Schitter,
• Elisabeth Scheucher,
• Andreas J. Steiner,
• Arnold E. Stütz,
• Martin Thonhofer,
• Chris A. Tarling,
• Stephen G. Withers,
• Jacqueline Wicki,
• Katrin Fantur,
• Eduard Paschke,
• Don J. Mahuran,
• Brigitte A. Rigat,
• Michael Tropak and
• Tanja M. Wrodnigg

Beilstein J. Org. Chem. 2010, 6, No. 21, doi:10.3762/bjoc.6.21

• -isopropylidene iminosugar 12. Starting from enol ether 10 [26][27], treatment with m-chloroperbenzoic acid gave the 5-O-chlorobenzoic ester via the corresponding 5,6-epoxide. This ester underwent hydrolysis under basic conditions to afford the L-arabino-hexos-5-ulose 11, which was immediately used for the next

Enantioselective synthesis of tricyclic amino acid derivatives based on a rigid 4-azatricyclo[5.2.1.0^2,6]decane skeleton

• Matthias Breuning,
• Tobias Häuser,
• Christian Mehler,
• Christian Däschlein,
• Carsten Strohmann,
• Andreas Oechsner and
• Holger Braunschweig

Beilstein J. Org. Chem. 2009, 5, No. 81, doi:10.3762/bjoc.5.81

• , and thus proximity-facilitated tandem hydride transfer/cyclization sequence [33]. Since the yields of rac-15 from the alkene rac-13 were low, we turned our attention to an alternative approach via the enol ether 18, which was available from 9 as a 1:1 mixture of E/Z-isomers by Wittig reaction with

• MeOCH=PPh3 (Scheme 4). The selective hydrolysis of the enol ether moiety in 18 in the presence of the N-Boc-protective group was achieved by using trichloroacetic acid. The desired endo-configured aldehyde 15 was thus available in only two steps in good 64% overall yield from 9. After oxidation of 15 to

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

Beilstein J. Org. Chem. 2009, 5, No. 33, doi:10.3762/bjoc.5.33

End game strategies towards the total synthesis of vibsanin E, 3-hydroxyvibsanin E, furanovibsanin A, and 3-O-methylfuranovibsanin A

• Brett D. Schwartz,
• Craig M. Williams and
• Paul V. Bernhardt

Beilstein J. Org. Chem. 2008, 4, No. 34, doi:10.3762/bjoc.4.34

• ) by a Claisen rearrangment (via the silyl enol ether) was not high yielding and produced many side products. Ozonolysis of 25 afforded the acetone sidechain (i.e. 26) in acceptable yield (50%). Other methods to unmask the ketone functionality failed, for example, dihydroxylation followed by oxidative

• procedure based on the epoxidation of silyl enol ethers. Ketone 23 was smoothly converted into the TBS enol ether 27 (85% yield) with TBS triflate, which was then treated with dimethyldioxirane (DMDO). When work up was restricted to a simple 1 M hydrochloric acid wash (i.e. separatory funnel) only the

• diketone dehydration (i.e. phosphorus pentaoxide [23]). For Padwa’s protocol the TMS enol ether 33 was required, which was obtained in 75% from sequential treatment of 30 with LDA and TMSCl. Subsequent reaction of 33 with Padwa’s electrophile 34 [24] and silver tetrafluoroborate gave a complex mixture with

Sordarin, an antifungal agent with a unique mode of action

• Huan Liang

Beilstein J. Org. Chem. 2008, 4, No. 31, doi:10.3762/bjoc.4.31

• (Swern), which was converted to the corresponding silyl enol ether. Saegusa oxidation [23] of the latter occurred regioselectively to afford 15, which underwent intramolecular cycloaddtion in benzene at 40 °C. A final deprotection gave sordaricin methyl ester (3) in 16 linear steps from 8 and 9 with an

• silylation / cycloaddition conditions that had successfully advanced 94 to 95, and it was recovered unchanged after many such attempts. Thus, extensive studies were performed to find suitable conditions for the silylation reaction. Silyl enol ether formation failed to occur under Corey-Gross (LDA, R3SiCl

Total synthesis of the indolizidine alkaloid tashiromine

• Stephen P. Marsden and
• Alison D. McElhinney

Beilstein J. Org. Chem. 2008, 4, No. 8, doi:10.1186/1860-5397-4-8

• after cross-metathesis, would allow access to chiral allylsilanes 9 with R1 being an alkoxy or acyloxy group. Furthermore, this would generate products 10 and/or 11 with a readily oxidised enol-ether/ester side chain for progression to tashiromine. We were, of course, mindful that these functions could

Contemporary organosilicon chemistry

• Steve Marsden

Beilstein J. Org. Chem. 2007, 3, No. 4, doi:10.1186/1860-5397-3-4

• . Notwithstanding the earlier, pioneering work of chemists such as Eaborn, 1968 was notable for many innovations we now take for granted, including the development of silyl enol ether chemistry by Stork and Hudrlik, and the eponymous olefination reaction by Peterson. These landmark papers triggered a massive growth

An efficient synthesis of novel pyrano[2,3-d]- and furopyrano[2,3-d]pyrimidines via indium- catalyzed multi- component domino reaction

• Dipak Prajapati and
• Mukut Gohain

Beilstein J. Org. Chem. 2006, 2, No. 11, doi:10.1186/1860-5397-2-11

• type of cycloaddition using an amino aldehyde and a benzyl enol ether in presence of ethylene diammonium acetate and triethyl orthoformate has been reported earlier but this method has its own merits and limitations.[36] Results and Discussions On treatment of 1,3-dimethylbarbituric acid 1, 4

Do α-acyloxy and α-alkoxycarbonyloxy radicals fragment to form acyl and alkoxycarbonyl radicals?

• Dennis P. Curran and
• Tiffany R. Turner

Beilstein J. Org. Chem. 2006, 2, No. 10, doi:10.1186/1860-5397-2-10

• atom transfer (Figure 2). The resulting radical 5 rebounds back to the enol ether in a 1,5-cyclization to provide 6. In the crucial self-terminating step, radical 6 is suggested to fragment to product 2 and radical X•. Related steps are involved in the formation of ketone 3 (not shown), except that the

• radical cyclization of enol ether 11a with tributyltin hydride (0.1 M) followed by chromatographic purification provided 14a in 95% yield as an inseparable 1:2 mixture of exo and endo isomers. Likewise, cyclization of enol ester 11b provided a 1:2 mixture of 14b-exo and 14b-endo in 68% isolated yield. The