Influence of spacer chain lengths and polar terminal groups on the mesomorphic properties of tethered 5-phenylpyrimidines

• Gundula F. Starkulla,
• Elisabeth Kapatsina,
• Angelika Baro,
• Frank Giesselmann,
• Stefan Tussetschläger,
• Martin Kaller and
• Sabine Laschat

Beilstein J. Org. Chem. 2009, 5, No. 63, doi:10.3762/bjoc.5.63

• 23 up to 60% yield. When 1,3-dibromopropane was used, 27% of the elimination product 9 was isolated as byproduct. For comparison the corresponding 4-allyloxy-4′-octylbiphenyl 11 was prepared in 49% yield by allylation of 4-hydroxy-4′-octylbiphenyl. Compound 3a was obtained by etherification of 5-(4

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

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

• sodium borohydride reduction of the remaining aldehyde, followed by alkylation of the resulting primary alcohol with methyl isocyanate to give 184. 6.4. Coleman. Allylation reaction and 1,4-quinone addition The Coleman group proposed an elegant synthesis of an enantiomerically pure mitosane. One of the

• key transformations involved an allylation reaction [139][140][141][142][143] between the allyl stannane 185 and the iminium formed in situ from the enantiomerically pure pyrrolidine 187 (Scheme 51) [144]. The reaction showed good diastereoselectivity, giving a 3:1 ratio of diastereomers favoring the

• substituent. When the allylation reaction was done with the iminium derived from pyrrolidine 186, no diastereoselectivity for the formation of 188 was observed. The bulkiness of the benzyl carbamate now proximal to the iminium ion was responsible for this poor result. The pyrrolidine 187 was synthesized from

Reduction of arenediazonium salts by tetrakis(dimethylamino)ethylene (TDAE): Efficient formation of products derived from aryl radicals

• Mohan Mahesh,
• John A. Murphy,
• Franck LeStrat and
• Hans Peter Wessel

Beilstein J. Org. Chem. 2009, 5, No. 1, doi:10.3762/bjoc.5.1

• donor in specific organometallic reactions, such as the chromium-mediated allylation of aldehydes and ketones [54][55] and the palladium-catalyzed reductive homo-coupling of aryl halides to afford the corresponding biaryls [56][57][58][59] illustrate further versatility of the reagent. The fact that

Recent progress on the total synthesis of acetogenins from Annonaceae

• Nianguang Li,
• Zhihao Shi,
• Yuping Tang,
• Jianwei Chen and
• Xiang Li

Beilstein J. Org. Chem. 2008, 4, No. 48, doi:10.3762/bjoc.4.48

• , Pagenkopf’s group reported the total synthesis of bullatacin (311) in an efficient route from commercial starting materials (Scheme 44) [105]. The bis(THF) core 319 was constructed from bis-epoxide 318 through double allylation and oxidative cyclization. Then titanium acetylide 320 was reacted with bis(THF

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

• directed towards bis-epi-3-hydroxyvibsanin E 51. This manoeuvre was further justified by the fact that diketone 40 was readily available via the allylation/Wacker protocol as described in Scheme 6. Considering the knowledge gained in Scheme 8, it was perceived best not to perform tricarbonyl reduction then

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

• persulfate-pyridine system [32]. The ensuing Ag(I) catalyzed oxidative radical cyclization proceeded in 85% yield. Racemic ketone 43 underwent regio- and stereoselective allylation under Corey-Enders conditions to provide olefin 44, which was subjected to Lemieux-Johnson cleavage to corresponding aldehyde

The use of chiral lithium amides in the desymmetrisation of N-trialkylsilyl dimethyl sulfoximines

• Matthew J. McGrath and
• Carsten Bolm

Beilstein J. Org. Chem. 2007, 3, No. 33, doi:10.1186/1860-5397-3-33

• in low yield (Table 2, Entry 4) presumably due to facile deprotonation of the product under the reaction conditions. A moderate yield was also obtained on allylation with allyl iodide (Table 2, Entry 5) but in this case the enantiomers could not be resolved by HPLC using a chiral column. A benzylic

Tether- directed synthesis of highly substituted oxasilacycles via an intramolecular allylation employing allylsilanes

• Peter J. Jervis and
• Liam R. Cox

Beilstein J. Org. Chem. 2007, 3, No. 6, doi:10.1186/1860-5397-3-6

• -mediated allylation to proceed in an intramolecular sense and therefore receive all the benefits associated with such processes. However, with the ability to cleave the tether post allylation, a product that is the result of a net intermolecular reaction can be obtained. In the present study, four

• diastereoisomeric β-silyloxy-α-methyl aldehydes, which contain an allylsilane tethered through the β-carbinol centre, have been prepared, in order to probe how the relative configuration of the two stereogenic centres affects the efficiency and selectivity of the intramolecular allylation. Results Syn-aldehydes

• , syn-4a and syn-4b, both react poorly, affording all four possible diastereoisomeric oxasilacycle products. In contrast, the anti aldehydes anti-4a and anti-4b react analogously to substrates that lack substitution at the α-site, affording only two of the four possible allylation products. Conclusion

Reaction of benzoxasilocines with aromatic aldehydes: Synthesis of homopterocarpans

• Míriam Álvarez-Corral,
• Cristóbal López-Sánchez,
• Leticia Jiménez-González,
• Antonio Rosales,
• Manuel Muñoz-Dorado and
• Ignacio Rodríguez-García

Beilstein J. Org. Chem. 2007, 3, No. 5, doi:10.1186/1860-5397-3-5

• of allylation reactions, [1] which has been used for the formation of carbo- and heterocycles. [2][3] We have applied it to the stereoselective synthesis of dihydrobenzofurans by means of the condensation of benzoxasilepines with aromatic aldehydes in the presence of Lewis acids. [4][5] Using this

Contemporary organosilicon chemistry

• Steve Marsden

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

• for asymmetric synthesis, and a new method for the electrochemical generation of silyl cations. Additionally, the unique nature of internet-based publishing means that the Series can grow as additional contributions are received: future papers in areas including allylation chemistry, stereoselective

Stereoselective α-fluoroamide and α-fluoro- γ-lactone synthesis by an asymmetric zwitterionic aza-Claisen rearrangement

• Kenny Tenza,
• Julian S. Northen,
• David O'Hagan and
• Alexandra M. Z. Slawin

Beilstein J. Org. Chem. 2005, 1, No. 13, doi:10.1186/1860-5397-1-13

• rearrangement (S)-2(methoxymethyl)pyrrolidine 22 was then explored as the chiral auxiliary.[25] This auxiliary was selected to include a co-ordinating oxygen in place of the bulky diphenylmethane group in 14 to compare steric versus co-ordination effects. Allylation then gave 23 as the required aza-Claisen

Methods for the synthesis of polyhydroxylated piperidines by diastereoselective dihydroxylation: Exploitation in the two-directional synthesis of aza-C-linked disaccharide derivatives

• Andrew Kennedy,
• Adam Nelson and
• Alexis Perry

Beilstein J. Org. Chem. 2005, 1, No. 2, doi:10.1186/1860-5397-1-2

• ). The N,O acetal was substituted,[40] both by reduction (→ 13) and by allylation (→ 14); the allylation reaction was highly diastereoselective (>95:<5 syn:anti), presumably as a result of a strong stereoelectronic preference for pseudo-axial attack on the intermediate iminium ion (with a pseudoaxial[40