Molecular architecture with carbohydrate functionalized β-peptides adopting 3₁₄-helical conformation

• Nitin J. Pawar,
• Navdeep S. Sidhu,
• George M. Sheldrick,
• Dilip D. Dhavale and
• Ulf Diederichsen

Beilstein J. Org. Chem. 2014, 10, 948–955, doi:10.3762/bjoc.10.93

• -peptide incorporation of sugar-β-amino acids are described providing the saccharide units as amino acid side chain. The respective sugar-β-amino acids are accessible by Michael addition of ammonia to sugar units derivatized as α,β-unsaturated esters. Three sugar units were incorporated in β-peptide

• conformation, thereby organizing the D-glucose, D-galactose or D-xylose carbohydrate epitopes on one face of the helix. Results and Discussion Synthesis of carbohydrate-β3-amino acids Key step for the synthesis of β3-sugar amino acids is the Michael addition of ammonia to α,β-unsaturated esters [47][48][49][50

Silver and gold-catalyzed multicomponent reactions

• Giorgio Abbiati and
• Elisabetta Rossi

Beilstein J. Org. Chem. 2014, 10, 481–513, doi:10.3762/bjoc.10.46

• several substituents and enolates 33 can be generated from methyl- or ethyl vinyl ketone, the corresponding α,β-unsaturated esters being unreactive. Enamines 34 arise from cyclic or linear C3–C5 ketones, acetophenones and β-diketones. It is noteworthy, that the reactions are highly regiospecific for

Additive-assisted regioselective 1,3-dipolar cycloaddition of azomethine ylides with benzylideneacetone

• Chuqin Peng,
• Jiwei Ren,
• Jun-An Xiao,
• Honggang Zhang,
• Hua Yang and
• Yiming Luo

Beilstein J. Org. Chem. 2014, 10, 352–360, doi:10.3762/bjoc.10.33

• with various dipolarophiles, such as α,β-unsaturated esters [21][22][23][24][25], dienones [26][27], α,β-unsaturated ketones [28][29][30], unsaturated aryl ketones [31][32][33] and electron-poor alkenes [34][35][36][37][38][39]. Among the studied α,β-unsaturated enones for 1,3-dipolar cycloaddition

Garner’s aldehyde as a versatile intermediate in the synthesis of enantiopure natural products

• Mikko Passiniemi and
• Ari M.P. Koskinen

Beilstein J. Org. Chem. 2013, 9, 2641–2659, doi:10.3762/bjoc.9.300

• reversed to >10:1 favouring adduct 68 [105]. α,β-Unsaturated esters can be synthesized from stabilized ylides. Reaction of 1 with ylide 69 is E-selective. Depending on the solvent, the E/Z-ratio can vary from 3:1 (in MeOH) [106] to 100:0 (THF [107] or benzene [108]). Since stabilized ylides are less

• reactive compared to their non-stabilized counterparts, they tend to epimerize the existing chiral center of 1 a lot less, if at all (pKaH value of 69 in DMSO is 8.5 compared to the pKa value of Ph3(Me)PBr, which is 22.5) [109]. Another method to prepare α,β-unsaturated esters is the Horner–Wadsworth

Palladium(II)-catalyzed Heck reaction of aryl halides and arylboronic acids with olefins under mild conditions

• Tanveer Mahamadali Shaikh and
• Fung-E Hong

Beilstein J. Org. Chem. 2013, 9, 1578–1588, doi:10.3762/bjoc.9.180

• ) was examined with different vinyl esters to determine the scope of this procedure. The results are given in Table 2, entries 18–20. Notably, the performances were in agreement with the previous expectations and yields are excellent in the preparation of α,β–unsaturated esters. The corresponding α,β

• -unsaturated esters 3o–3q were obtained in 90–95% yields, respectively. Heck reaction of arylboronic acids with olefins The phosphine- and base-free coupling of arylboronic acids with olefins under mild reaction conditions were studied as well to broaden the scope of cross-coupling reactions. To search for the

A reductive coupling strategy towards ripostatin A

• Kristin D. Schleicher and
• Timothy F. Jamison

Beilstein J. Org. Chem. 2013, 9, 1533–1550, doi:10.3762/bjoc.9.175

• well tolerated for the reaction using γ-hydroxy-α,β-enones. Although the presence of chirality at the δ-position allows for diastereoselective intramolecular oxy-Michael addition of hemiacetal-derived alkoxides into α,β-unsaturated esters, the extension of this reaction to ketones was not successful

Efficient synthesis of β’-amino-α,β-unsaturated ketones

• Isabelle Abrunhosa-Thomas,
• Aurélie Plas,
• Nishanth Kandepedu,
• Pierre Chalard and
• Yves Troin

Beilstein J. Org. Chem. 2013, 9, 486–495, doi:10.3762/bjoc.9.52

• under different protocols in which the stereoselectivity of the reaction can be introduced through the use of a chiral catalyst [9][10] (Lewis acid, Brønsted acids, L-proline, Cinchona alkaloids derivatives, thioureas, etc.), or by the addition of chiral amines to α,β-unsaturated esters [11][12] or the

Efficient synthesis of 1,3-diaryl-4-halo-1H-pyrazoles from 3-arylsydnones and 2-aryl-1,1-dihalo-1-alkenes

• Yiwen Yang,
• Chunxiang Kuang,
• Hui Jin,
• Qing Yang and
• Zhongkui Zhang

Beilstein J. Org. Chem. 2011, 7, 1656–1662, doi:10.3762/bjoc.7.195

• ], alkenyl arenes [19], 1,3-dienes [20][21], α,β-unsaturated esters [19][22] and nitriles [23], phosphane oxides [24] or with alkynyl silanes [18], stannanes [18][25][26], arenes [27][28], esters [29][30][31][32][33], boronic esters [34][35]. However, the cycloaddition of sydnones with 1,1-dihaloalkenes is

Application of the diastereoselective photodeconjugation of α,β-unsaturated esters to the synthesis of gymnastatin H

• Ludovic Raffier and
• Olivier Piva

Beilstein J. Org. Chem. 2011, 7, 151–155, doi:10.3762/bjoc.7.21

• configuration of the C-6 centre of the target molecule was controlled. Keywords: amide; diastereoselective protonation; dienol; isomerisation; Wittig reaction; Introduction The photodeconjugation of α,β-unsaturated esters 1 – which bear at least one hydrogen atom on γ-position – allows a straightforward

Catalytic synthesis of (E)-α,β-unsaturated esters from aldehydes and 1,1-diethoxyethylene

• Rubén Manzano,
• Lidia Ozores,
• Andreas Job,
• Lars Rodefeld and
• Benjamin List

Beilstein J. Org. Chem. 2009, 5, No. 3, doi:10.3762/bjoc.5.3

• high yielding synthesis of α,β-unsaturated esters from aldehydes and 1,1-diethoxyethylene was developed. Keywords: 1,1-diethoxyethylene; α,β-unsaturated esters; Introduction A number of reactions transforming aldehydes into α,β-unsaturated esters have been developed and especially Wittig reaction

• leads to the formation of water and CO2 as the only by-products (Scheme 1, eq 3) [23][24]. Here we describe as a new approach, the boronic acid-catalyzed condensation of ketene dialkyl acetal with aldehydes to furnish α,β-unsaturated esters in good yields and reliably high (E)-stereoselectivities

• reaction was stirred at the same temperature for 12 h. The solvent was removed under vacuum, and the crude material was purified by flash chromatography to afford the pure product (silica gel, hexane/EtOAc 95/5). Conversions of aldehydes into α,β-unsaturated esters. A plausible mechanism. Selected results

The role of an aromatic group in remote chiral induction during conjugate addition of α-sulfonylallylic carbanions to ethyl crotonate

• Shlomo Levinger,
• Ranjeet Nair and
• Alfred Hassner

Beilstein J. Org. Chem. 2008, 4, No. 32, doi:10.3762/bjoc.4.32

• -sulfonylallylic carbanions to open-chain α,β-unsaturated esters, which has been shown to proceed anti-diastereoselectively [2][13] and with the N(1)R*,3S*,4R* relative configuration predominating [1], we assign our major and minor products structures 3 and 4 respectively (showing in Scheme 1 only one enantiomer

Efficient 1,4-addition of α-substituted fluoro(phenylsulfonyl)methane derivatives to α,β-unsaturated compounds

• G. K. Surya Prakash,
• Xiaoming Zhao,
• Sujith Chacko,
• Fang Wang,
• Habiba Vaghoo and
• George A. Olah

Beilstein J. Org. Chem. 2008, 4, No. 17, doi:10.3762/bjoc.4.17

• -addition to α,β-unsaturated esters, ketones, sulfone, nitriles and propynoates. Supporting Information Supporting Information File 83: Experimental procedures, full spectroscopic data and spectra. Supporting Information File 84: Spectra. Acknowledgements Support of our work by the Loker Hydrocarbon

Flexible synthetic routes to poison- frog alkaloids of the 5,8-disubstituted indolizidine- class I: synthesis of common lactam chiral building blocks and application to the synthesis of (-)-203A, (-)-205A, and (-)-219F

• Naoki Toyooka,
• Dejun Zhou,
• Hideo Nemoto,
• H. Martin Garraffo,
• Thomas F. Spande and
• John W. Daly

Beilstein J. Org. Chem. 2007, 3, No. 29, doi:10.1186/1860-5397-3-29

• and 8 with Super-Hydride gave the corresponding alcohols (9, 10) in good yield. Swern oxidation of 9 or 10 followed by Horner-Emmons reaction of the resulting aldehydes afforded the α,β-unsaturated esters (11, 12) each in 97% yield. Hydrogenation of the double bond in 11 or 12 over 20% Pd(OH)2 and