Aza-Diels–Alder reaction between N-aryl-1-oxo-1H-isoindolium ions and tert-enamides: Steric effects on reaction outcome

• Amitabh Jha,
• Ting-Yi Chou,
• Zainab ALJaroudi,
• Bobby D. Ellis and
• T. Stanley Cameron

Beilstein J. Org. Chem. 2014, 10, 848–857, doi:10.3762/bjoc.10.81

• –Alder reaction [23][24] and dehydration sequence [25][26] (Scheme 1). As mentioned earlier, N-aryl-1-oxo-1H-isoindolium ions (A, Scheme 1) undergo [4 + 2] imino-Diels–Alder cyclization with electron-rich alkenes [11][12][13][14][15][16][17], the steric effects on the outcome of these reactions has not

• the boat”) of the electron-donating substituents on the dienophile (Scheme 2). To further understand the steric effects, we elected to study this transformation on ortho-substituted aniline-derived N-acyliminium cations. Nine N-(2-substituted-aryl)-3-hydroxyisoindolinones (Table 2) were prepared using

Synthesis of chiral N-phosphinyl α-imino esters and their application in asymmetric synthesis of α-amino esters by reduction

• Yiwen Xiong,
• Haibo Mei,
• Lingmin Wu,
• Jianlin Han,
• Yi Pan and
• Guigen Li

Beilstein J. Org. Chem. 2014, 10, 653–659, doi:10.3762/bjoc.10.57

• -substituent led to lower yield due to steric effects (Table 2, entry 7). Besides, the reaction with ethyl ester also worked well and resulted in a slightly lower yield (Table 2, entry 11). Optimization of the asymmetric reduction reaction conditions Then, the obtained chiral N-phosphinyl α-imino esters were

One-pot three-component synthesis and photophysical characteristics of novel triene merocyanines

• Christian Muschelknautz,
• Robin Visse,
• Jan Nordmann and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2014, 10, 599–612, doi:10.3762/bjoc.10.51

• of the merocyanines 8 begins with a 1,4-dipolar cyclization of 13 furnishing the highly substituted cyclobutene intermediate 14. Finally, the conrotatory electrocyclic ring opening of the cyclobutene occurs under thermodynamic control, which is obviously only governed by steric effects as reflected

Isocyanide-based multicomponent reactions towards cyclic constrained peptidomimetics

• Gijs Koopmanschap,
• Eelco Ruijter and
• Romano V.A. Orru

Beilstein J. Org. Chem. 2014, 10, 544–598, doi:10.3762/bjoc.10.50

• -3CR-approach with enantiopure monoterpene-based β-amino acids [43] (19, Scheme 8), giving 22 as major isomer [44]. The stereoselectivity for 22 was explained by the steric effects of the dimethyl bridge that might prefer a Re-attack of the isocyanide. Compared to methanol, again the reaction in water

Concise, stereodivergent and highly stereoselective synthesis of cis- and trans-2-substituted 3-hydroxypiperidines – development of a phosphite-driven cyclodehydration

• Peter H. Huy,
• Julia C. Westphal and
• Ari M. P. Koskinen

Beilstein J. Org. Chem. 2014, 10, 369–383, doi:10.3762/bjoc.10.35

• secondary OH group proceeded (with PPh3 and P(OEt)3) in very high chemoselectivity most likely due to steric effects. The corresponding aziridine of 9a clearly resulting from activation of the secondary hydroxy group and subsequent fast 3-exo-trig cyclisation was only obtained as a sideproduct at higher

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

• ′-diarylspiro(indoline-3,2′-pyrrolidin)-2-one was formed when using chalcone or dienone as dipolarophiles [20][31]. Presumably, this might be attributed to the electronic and steric effects of the acetyl group. Therefore, reaction conditions including various solvents and additives (Table 1, entries 2–9) were

Oligomeric epoxide–amine adducts based on 2-amino-N-isopropylacetamide and α-amino-ε-caprolactam: Solubility in presence of cyclodextrin and curing properties

• Julian Fischer and
• Helmut Ritter

Beilstein J. Org. Chem. 2013, 9, 2803–2811, doi:10.3762/bjoc.9.315

• randomly methylated β-cyclodextrin (RAMEB-CD) were added (9β). After that, the cloud point shifted significantly up to 36 °C, which is remarkable since PNIPAM does not interact with β-CD [14]. Explanation for this can be steric effects, since the isopropyl group in our system 9 is placed not so close at

Diastereoselectivity in the Staudinger reaction of pentafluorosulfanylaldimines and ketimines

• Alexander Penger,
• Cortney N. von Hahmann,
• Alexander S. Filatov and
• John T. Welch

Beilstein J. Org. Chem. 2013, 9, 2675–2680, doi:10.3762/bjoc.9.303

• number of different ylides [16]. The reactions of α-pentafluorosulfanyl carbonyl compounds are governed by a combination of the substantial dipole moment and unique steric effects of the octahedral SF5 group. Aliphatic SF5-containing derivatives of biologically active compounds are not well-known. One

Recent advances in transition metal-catalyzed Csp²-monofluoro-, difluoro-, perfluoromethylation and trifluoromethylthiolation

• Grégory Landelle,
• Armen Panossian,
• Sergiy Pazenok,
• Jean-Pierre Vors and
• Frédéric R. Leroux

Beilstein J. Org. Chem. 2013, 9, 2476–2536, doi:10.3762/bjoc.9.287

• initiator. The reaction was achieved with α,β-unsaturated carboxylic acids bearing electron-donating groups, as well as with heteroarene substituted acrylic acids, and the desired products were isolated in modest to good yields (Table 30). Steric effects do not appear to have an influence on the outcome of

ML212: A small-molecule probe for investigating fluconazole resistance mechanisms in Candida albicans

• Willmen Youngsaye,
• Cathy L. Hartland,
• Barbara J. Morgan,
• Amal Ting,
• Partha P. Nag,
• Benjamin Vincent,
• Carrie A. Mosher,
• Joshua A. Bittker,
• Sivaraman Dandapani,
• Michelle Palmer,
• Luke Whitesell,
• Susan Lindquist,
• Stuart L. Schreiber and
• Benito Munoz

Beilstein J. Org. Chem. 2013, 9, 1501–1507, doi:10.3762/bjoc.9.171

• different positions about the ring to probe for further electronic and steric effects associated with this region (Table 3). With regards to steric requirements, it appears that neither the para- (compounds 30–34) nor ortho-positions (compounds 39 and 40) are particularly amenable to functionalization

True and masked three-coordinate T-shaped platinum(II) intermediates

• Manuel A. Ortuño,
• Salvador Conejero and
• Agustí Lledós

Beilstein J. Org. Chem. 2013, 9, 1352–1382, doi:10.3762/bjoc.9.153

Incorporation of perfluorohexyl-functionalised thiophenes into oligofluorene-truxenes: synthesis and physical properties

• Neil Thomson,
• Alexander L. Kanibolotsky,
• Joseph Cameron,
• Tell Tuttle,
• Neil J. Findlay and
• Peter J. Skabara

Beilstein J. Org. Chem. 2013, 9, 1243–1251, doi:10.3762/bjoc.9.141

• the p-orbital overlap, breaking the effective conjugation length [15]. This planarity can be perturbed by the steric effects of substituents attached to the hetero- or carbocycles in the conjugated backbone. In order to observe if the position of the perfluorohexyl chains would have an effect, two

Conformational analysis and intramolecular interactions in monosubstituted phenylboranes and phenylboronic acids

• Josué M. Silla,
• Rodrigo A. Cormanich,
• Roberto Rittner and
• Matheus P. Freitas

Beilstein J. Org. Chem. 2013, 9, 1127–1134, doi:10.3762/bjoc.9.125

• corresponding conformers appreciably populated, because of steric effects and the loss of πCC→pB resonance. Thus, the results found earlier for 2-fluorophenol about the lack of intramolecular hydrogen bonding are now corroborated. Keywords: conformational analysis; hydrogen bond; interactions with boron

C–C Bond formation catalyzed by natural gelatin and collagen proteins

• Dennis Kühbeck,
• Basab Bijayi Dhar,
• Eva-Maria Schön,
• Carlos Cativiela,
• Vicente Gotor-Fernández and
• David Díaz Díaz

Beilstein J. Org. Chem. 2013, 9, 1111–1118, doi:10.3762/bjoc.9.123

• nitromethane (pKa = 10.2) the yield increased considerably (Table 3, entries 2, 6, 10 vs. 1, 5, 9, respectively), albeit without significant diastereoselectivity. Thus, acidity of the nitroalkane plays here a more important role than steric effects [28]. It is worth mentioning that control experiments in the

Methylidynetrisphosphonates: Promising C₁ building block for the design of phosphate mimetics

• Vadim D. Romanenko and
• Valery P. Kukhar

Beilstein J. Org. Chem. 2013, 9, 991–1001, doi:10.3762/bjoc.9.114

• hydrogen atom attached to the bridge carbon in methylenebisphosphonates by a third ionisable phosphonate moiety results in supercharged isosteric systems relative to pyrophosphoric acid [7]. It was also demonstrated that steric effects play a significant role in trisphosphonate chemistry and allow

Alkyne hydroarylation with Au N-heterocyclic carbene catalysts

• Cristina Tubaro,
• Marco Baron,
• Andrea Biffis and
• Marino Basato

Beilstein J. Org. Chem. 2013, 9, 246–253, doi:10.3762/bjoc.9.29

• reaction. This observation indicates that the reactivity of the complexes is not hampered by steric effects, as complexes with ligands of widely different steric bulk, such as II and V, exhibit similar performance. On the other hand, the complexes deactivate with time at different rates, depending on the

Development of peptidomimetic ligands of Pro-Leu-Gly-NH₂ as allosteric modulators of the dopamine D₂ receptor

• Swapna Bhagwanth,
• Ram K. Mishra and
• Rodney L. Johnson

Beilstein J. Org. Chem. 2013, 9, 204–214, doi:10.3762/bjoc.9.24

• adverse steric effects and that this may be responsible for the observed weaker activity seen with 62 and 63. Conclusion The development of PLG peptidomimetic probes has proved valuable in helping to elucidate the structural and molecular mechanism by which an endogenous neuropeptide, PLG, modulates

Theoretical study on β-cyclodextrin inclusion complexes with propiconazole and protonated propiconazole

• Adrian Fifere,
• Narcisa Marangoci,
• Stelian Maier,
• Adina Coroaba,
• Dan Maftei and
• Mariana Pinteala

Beilstein J. Org. Chem. 2012, 8, 2191–2201, doi:10.3762/bjoc.8.247

• geometry optimization, due to its improved description of hydrogen bonds and steric effects [8][9][10]. Advanced methods, such as Hartree–Fock (HF) and density functional theory (DFT), were also applied in cyclodextrin chemistry to explain experimental data [11][12]. Very often, ab initio methods are used

Metal–ligand multiple bonds as frustrated Lewis pairs for C–H functionalization

• Matthew T. Whited

Beilstein J. Org. Chem. 2012, 8, 1554–1563, doi:10.3762/bjoc.8.177

• [17], carbene [18], and borylene complexes [19], among others [20][21][22][23]. Either bonding situation can be described as electronic frustration [24], since sterics do not play a primary role in separating acidic and basic reactive sites on a molecule. Steric effects nevertheless play an important

Reactions of nitroxides XIII: Synthesis of the Morita–Baylis–Hillman adducts bearing a nitroxyl moiety using 4-acryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl as a starting compound, and DABCO and quinuclidine as catalysts

• Jerzy Zakrzewski

Beilstein J. Org. Chem. 2012, 8, 1515–1522, doi:10.3762/bjoc.8.171

• that the effects on the reaction of aryl, benzyl, alkyl, and functionalized alkyl acrylic esters with benzaldehyde and furfuraldehyde in the presence of DABCO, strongly depend upon the electronic and steric effects of the ester part. The “unreactivity” of acrylates increases with steric hindrance and

Synthesis and characterization of low-molecular-weight π-conjugated polymers covered by persilylated β-cyclodextrin

• Aurica Farcas,
• Ana-Maria Resmerita,
• Andreea Stefanache,
• Mihaela Balan and
• Valeria Harabagiu

Beilstein J. Org. Chem. 2012, 8, 1505–1514, doi:10.3762/bjoc.8.170

• morphology and thermal properties of the PDOF-BTc rotaxane copolymer compared to its noncomplexed PDOF-BT homologue. In contrast, the number-average molecular weight (Mn) of PDOF-BTc rotaxane copolymer indicated lower values suggesting that the condensation reaction is subjected to steric effects of the

• confirms that PS-βCD can be used as a host macrocycle molecule in the synthesis of a main-chain polyrotaxane with alternating fluorene-bithiophene moieties. Lower values of number-average molecular weight (Mn) of the rotaxane copolymer suggested that the condensation reaction is subjected to steric effects

Cation affinity numbers of Lewis bases

• Christoph Lindner,
• Raman Tandon,
• Boris Maryasin,
• Evgeny Larionov and
• Hendrik Zipse

Beilstein J. Org. Chem. 2012, 8, 1406–1442, doi:10.3762/bjoc.8.163

• to the respective mono-substituted amine (e.g., NMe2n-Pr (27) with MCA(27) = 552.1 kJ/mol). However, even in systems with linear alkyl substituents unfavorable steric effects appear to exist between the alkyl substituents, and confining the alkyl groups to a bicyclic cage structure as in quinuclidine

• (53) thus raises the MCA value considerably to MCA(53) = +580.6 kJ/mol. For amines with branched or cyclic substituents a further erosion of MCA values can be observed due to increasing steric effects in the methyl cation adducts. The following trends in amine MCA values can therefore be observed for

• amines Me2N(iPr) (26, MCA = 551.7 kJ/mol), MeN(iPr)2 (39, MCA = 557.3 kJ/mol) and N(iPr)3 (16, MCA = 536.0 kJ/mol) is helpful. In the absence of steric effects a systematic increase in the MCA value is expected on replacing methyl by isopropyl substituents. However, the number of gauche interactions

Conformational analysis, stereoelectronic interactions and NMR properties of 2-fluorobicyclo[2.2.1]heptan-7-ols

• Fátima M. P. de Rezende,
• Marilua A. Moreira,
• Rodrigo A. Cormanich and
• Matheus P. Freitas

Beilstein J. Org. Chem. 2012, 8, 1227–1232, doi:10.3762/bjoc.8.137

• hyperconjugation); this can be achieved by deleting all interactions involving antibonding and Rydberg orbitals in a molecule and then computing the energy of this hypothetical system. Accordingly, the global minimum was found to be the most destabilized form in terms of steric effects (possibly because of the nF

Catalyst-free and solvent-free Michael addition of 1,3-dicarbonyl compounds to nitroalkenes by a grinding method

• Zong-Bo Xie,
• Na Wang,
• Ming-Yu Wu,
• Ting He,
• Zhang-Gao Le and
• Xiao-Qi Yu

Beilstein J. Org. Chem. 2012, 8, 534–538, doi:10.3762/bjoc.8.61

• moderate diastereoselectivity (dr = 82:18, Table 1, entry 12 ). For the purpose of comparing the reactivity of different nitroalkenes with 1,3-cyclopentanedione, another group of experiments was performed, and a marked difference existed among various nitroalkenes, owing to steric effects or electronic

On the control of secondary carbanion structure utilising ligand effects during directed metallation

• Andrew E. H. Wheatley,
• Jonathan Clayden,
• Ian H. Hillier,
• Alison Campbell Smith,
• Mark A. Vincent,
• Laurence J. Taylor and
• Joanna Haywood

Beilstein J. Org. Chem. 2012, 8, 50–60, doi:10.3762/bjoc.8.5

• deprotonation on electronic grounds [1][2]. Moreover, steric effects have also been found to play an important role. Hence, whereas the formation of primary [18] and secondary [19] carbanions through lateral deprotonation has been known for many years, it is only very recently that the analogous formation of