Synthesis of indole–cycloalkyl[b]pyridine hybrids via a four-component six-step tandem process

• Muthumani Muthu,
• Rakkappan Vishnu Priya,
• Abdulrahman I. Almansour,
• Raju Suresh Kumar and
• Raju Ranjith Kumar

Beilstein J. Org. Chem. 2018, 14, 2907–2915, doi:10.3762/bjoc.14.269

• [b]pyridine-3-carbonitrile hybrid heterocycles 7 with an ortho/ortho-para/ortho-meta substituted phenyl ring at C-4 may be attributed to the axial chirality induced in these molecules due to the restricted rotation of the C–C single bond. The steric hindrance exerted between the nitrile group at C-3

Unnatural α-amino ethyl esters from diethyl malonate or ethyl β-bromo-α-hydroxyiminocarboxylate

• Eloi P. Coutant,
• Vincent Hervin,
• Glwadys Gagnot,
• Candice Ford,
• Racha Baatallah and
• Yves L. Janin

Beilstein J. Org. Chem. 2018, 14, 2853–2860, doi:10.3762/bjoc.14.264

• encountered when steric hindrance became a previously unreported limiting factor for the oximation of compound 34, and to a lesser degree compounds 36 or 39. Finally, the use of the ethyl β-bromo-α-hydroxyimino carboxylate 47 in a [2 + 4] cycloaddition reaction led us to suggest a simple, reliable and robust

Pd-Catalyzed microwave-assisted synthesis of phosphonated 13α-estrones as potential OATP2B1, 17β-HSD1 and/or STS inhibitors

• Rebeka Jójárt,
• Szabolcs Pécsy,
• György Keglevich,
• Mihály Szécsi,
• Réka Rigó,
• Csilla Özvegy-Laczka,
• Gábor Kecskeméti and
• Erzsébet Mernyák

Beilstein J. Org. Chem. 2018, 14, 2838–2845, doi:10.3762/bjoc.14.262

• ). The steric hindrance resulting from the presence of ring B near C-4 might be the main cause for the harsher reaction conditions. This is in agreement with our recently published Sonogashira coupling procedure, which required higher temperatures starting from 4-regioisomers in comparison with those

Enhanced single-isomer separation and pseudoenantiomer resolution of new primary rim heterobifunctionalized α-cyclodextrin derivatives

• Iveta Tichá,
• Gábor Benkovics,
• Milo Malanga and
• Jindřich Jindřich

Beilstein J. Org. Chem. 2018, 14, 2829–2837, doi:10.3762/bjoc.14.261

• indirect method generally led to selectively homobifunctionalized CDs. In contrast, heterobifunctionalized CDs have been prepared via multistep synthesis (depending on the steric hindrance of the moiety on the CD scaffold and on the bulkiness of reagents [22]) or by modification of homobifunctionalized CDs

Synthesis of dihydroquinazolines from 2-aminobenzylamine: N³-aryl derivatives with electron-withdrawing groups

• Nadia Gruber,
• Jimena E. Díaz and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2018, 14, 2510–2519, doi:10.3762/bjoc.14.227

• %) to excellent (>80%) overall yields from 2-ABA in three steps (Table 3, last column). Regarding the ring-closure step, Table 3 shows a clear dependence of the reaction times with steric hindrance of the amide group (R) in the substrate, displaying the order R = CH3 < CH2CH3 < CH(CH3)2 << C(CH3)3. In

Bi-mediated allylation of aldehydes in [bmim][Br]: a mechanistic investigation

• Mrunesh Koli,
• Sucheta Chatterjee,
• Subrata Chattopadhyay and
• Dibakar Goswami

Beilstein J. Org. Chem. 2018, 14, 2198–2203, doi:10.3762/bjoc.14.193

• , entries 1–7). Steric hindrance was not detrimental to the yield of the reaction, as it was evident from the allylation of 1e, bearing a substituent ortho to the aldehyde function (Table 2, entry 4). The aliphatic aldehydes 1i and 1j also reacted similarly to give the homoallylic alcohols 2i and 2j

Synthesis and post-functionalization of alternate-linked-meta-para-[2ⁿ.1ⁿ]thiacyclophanes

• Wout De Leger,
• Koen Adriaensen,
• Koen Robeyns,
• Luc Van Meervelt,
• Joice Thomas,
• Björn Meijers,
• Mario Smet and
• Wim Dehaen

Beilstein J. Org. Chem. 2018, 14, 2190–2197, doi:10.3762/bjoc.14.192

• ] adduct 19. Traces of unidentified oligomers and functionalized [2 + 2] macrocycle were also observed in the reaction mixture. It can be argued that, due to steric hindrance, the alkylation of macrocycle 6 is slow. The less sterically hindered cyclic trimer 7 and the linear oligomers are therefore faster

Tetrathiafulvalene – a redox-switchable building block to control motion in mechanically interlocked molecules

• Hendrik V. Schröder and
• Christoph A. Schalley

Beilstein J. Org. Chem. 2018, 14, 2163–2185, doi:10.3762/bjoc.14.190

• rotaxanes in which the wheel is only held on the axle component by steric hindrance of stopper groups, a catenane is a truly topologically interlocked species bearing a mechanical bond. However, the construction, chemical behavior, and operation of structurally related rotaxanes and catenanes are often very

D-Fructose-based spiro-fused PHOX ligands: synthesis and application in enantioselective allylic alkylation

• Michael R. Imrich,
• Jochen Kraft,
• Cäcilia Maichle-Mössmer and
• Thomas Ziegler

Beilstein J. Org. Chem. 2018, 14, 2082–2089, doi:10.3762/bjoc.14.182

• influence on the ratio too. This could be explained by steric hindrance of R2 at the nucleophilic attack at 9b. However, the described model does not work for entries 6–9 in Table 1, because we observed significant amounts of 11 even with very bulky protective groups like benzoyl or pivaloyl. In

Rational design of boron-dipyrromethene (BODIPY) reporter dyes for cucurbit[7]uril

• Mohammad A. Alnajjar,
• Jürgen Bartelmeß,
• Robert Hein,
• Pichandi Ashokkumar,
• Mohamed Nilam,
• Werner M. Nau,
• Knut Rurack and
• Andreas Hennig

Beilstein J. Org. Chem. 2018, 14, 1961–1971, doi:10.3762/bjoc.14.171

• previously noted for water/DMSO mixtures [56]. The attachment of the BODIPY chromophore to the anchor groups thus reduces the binding constant by an additional factor of 10 for the aniline meso-group and by a factor of 1000 for the tetrafluoroaniline group in 4. We ascribe this to steric hindrance between

Asymmetric Michael addition reactions catalyzed by calix[4]thiourea cyclohexanediamine derivatives

• Zheng-Yi Li,
• Hong-Xiao Tong,
• Yuan Chen,
• Hong-Kui Su,
• Tangxin Xiao,
• Xiao-Qiang Sun and
• Leyong Wang

Beilstein J. Org. Chem. 2018, 14, 1901–1907, doi:10.3762/bjoc.14.164

• nitrostyrene 7a lacking substituents has minimal steric hindrance and tends to bind with the calixarene cavity by supramolecular host–guest interactions which could further improve the enantioselectivity. In addition, electronic effects of the substituents on the aromatic ring showed a significant influence on

• reaction, the question arises, which one is activated by the thiourea group through double hydrogen bonding. Based on the better enantioselectivity observed for product 9a over 9b–k, it was deduced that the binding of the nitroolefin with the calixarene cavity might be affected by the steric hindrance of

Synthesis of new tricyclic 5,6-dihydro-4H-benzo[b][1,2,4]triazolo[1,5-d][1,4]diazepine derivatives by [3⁺ + 2]-cycloaddition/rearrangement reactions

• Lin-bo Luan,
• Zi-jie Song,
• Zhi-ming Li and
• Quan-rui Wang

Beilstein J. Org. Chem. 2018, 14, 1826–1833, doi:10.3762/bjoc.14.155

• give the desired product 10y. This result could be attributed to the increased steric hindrance in nitrile moiety. As can be seen from Scheme 3, equally satisfactory results could be obtained from the reaction of other acetoxyazo compounds 8 with several different substituents on the benzene ring, as

An amine protecting group deprotectable under nearly neutral oxidative conditions

• Shahien Shahsavari,
• Chase McNamara,
• Mark Sylvester,
• Emily Bromley,
• Savannah Joslin,
• Bao-Yuan Lu and
• Shiyue Fang

Beilstein J. Org. Chem. 2018, 14, 1750–1757, doi:10.3762/bjoc.14.149

• of Dmoc due to its higher steric hindrance. Such side reactions could be a serious issue in some situations [18]. Results and Discussion To protect amines, compound 4 was prepared readily by reacting deprotonated 1,3-dithiane with acetone followed by treating with p-nitrophenylchloroformate (see

Host–guest complexes of conformationally flexible C-hexyl-2-bromoresorcinarene and aromatic N-oxides: solid-state, solution and computational studies

• Rakesh Puttreddy,
• Ngong Kodiah Beyeh,
• S. Maryamdokht Taimoory,
• Daniel Meister,
• John F. Trant and
• Kari Rissanen

Beilstein J. Org. Chem. 2018, 14, 1723–1733, doi:10.3762/bjoc.14.146

• aromatic rings in 6@BrC6 is caused by either steric hindrance or unfavourable positioning. This prevents the formation of stronger C–H···π interactions; consequently, 6@BrC6 is only stabilised by weak C–C contacts at distances of 3.31 Å. However, 7 with similar ‘h’ values, due to the bulky methoxy group on

Design, synthesis and structure of novel G-2 melamine-based dendrimers incorporating 4-(n-octyloxy)aniline as a peripheral unit

• Cristina Morar,
• Pedro Lameiras,
• Attila Bende,
• Gabriel Katona,
• Emese Gál and
• Mircea Darabantu

Beilstein J. Org. Chem. 2018, 14, 1704–1722, doi:10.3762/bjoc.14.145

• ΔE values for the rotational diastereomerism decreased (i) with the decrease of the steric hindrance between the three (hetero)aryl rings in rotamers (s–s) > (a–s) > (a–a), and (ii) with the weakening of the π-deficiency of the s-triazine, 2a > 3. The same optimal geometry (a–a) was found in

• states with rapid and free rotation about all the C(s-triazine)–N(exocyclic) bonds. In contrast, in the 1H NMR spectrum of dendrimer 5 recorded at 90 °C, multiple resonances (Table 3 and Figure 3) were displayed by the indicative NH protons, suggesting the occurrence of a significant peripheral steric

• hindrance, starburst effect [18][58][59], against authentic free rotation upon heating. This fact was not quite surprising because we previously reported a related situation in the case of some G-0 dendrons as N,N’-disubstituted 2-chloro-4,6-diamino-s-triazines with bulky azaspirodecane and propane-1,3-diol

Anomeric modification of carbohydrates using the Mitsunobu reaction

• Julia Hain,
• Patrick Rollin,
• Werner Klaffke and
• Thisbe K. Lindhorst

Beilstein J. Org. Chem. 2018, 14, 1619–1636, doi:10.3762/bjoc.14.138

• . Stereoselectivity in the Mitsunobu synthesis of catechol glycosides in the gluco- and manno-series [56]. Formation of a 1,2-cis glycoside 80 assisted by steric hindrance of the β-face of the disaccharide through the DTBS protection. DTBS: di-tert-butylsilylene; Troc: 2,2,2-trichloroethoxycarbonyl [22

Glycosylation reactions mediated by hypervalent iodine: application to the synthesis of nucleosides and carbohydrates

• Yuichi Yoshimura,
• Hideaki Wakamatsu,
• Yoshihiro Natori,
• Yukako Saito and
• Noriaki Minakawa

Beilstein J. Org. Chem. 2018, 14, 1595–1618, doi:10.3762/bjoc.14.137

• 28, by treating with 2,4-bis(trimethylsilyl)uracil (29) and excess diisopropylethylamine (DIPEA) in the presence of TMSOTf, gave 4’-thiouridine derivative 30 in a good yield. The reaction stereoselectively proceeded and resulted the predominant formation of the β-anomer due to steric hindrance of the

Recent advances in phosphorescent platinum complexes for organic light-emitting diodes

• Cristina Cebrián and
• Matteo Mauro

Beilstein J. Org. Chem. 2018, 14, 1459–1481, doi:10.3762/bjoc.14.124

• properties (Figure 6) [37]. The intermolecular interaction was finely tuned as a function of the steric hindrance of the acac-type ancillary ligand, which had a profound impact on the emission quantum yield. Characterization of the electroluminescence performances of these complexes in mixed-matrix OLED led

• suggests that the steric hindrance imparted by the diisopropylphenyl group is important for avoiding intermolecular interactions. Furthermore, OLED using complex 41 as emitting materials showed good performances with maximum EQE of 22.3%. In a following study, a second series of tetradentate platinum

Recent applications of chiral calixarenes in asymmetric catalysis

• Mustafa Durmaz,
• Erkan Halay and
• Selahattin Bozkurt

Beilstein J. Org. Chem. 2018, 14, 1389–1412, doi:10.3762/bjoc.14.117

• used as catalyst. This result could be ascribed to the effect of steric hindrance on the upper rim of calix[4]arene. So, the optimization and substrate scope studies were performed by using chiral catalyst 69f and up to 98% ee was obtained (Scheme 30). In order to confirm the role of the calixarene

A three-armed cryptand with triazine and pyridine units: synthesis, structure and complexation with polycyclic aromatic compounds

• Claudia Lar,
• Adrian Woiczechowski-Pop,
• Attila Bende,
• Ioana Georgeta Grosu,
• Natalia Miklášová,
• Elena Bogdan,
• Niculina Daniela Hădade,
• Anamaria Terec and
• Ion Grosu

Beilstein J. Org. Chem. 2018, 14, 1370–1377, doi:10.3762/bjoc.14.115

• respect to the central benzene ring. In such twisted conformations there is a remarkable steric hindrance between the ortho hydrogen atoms of the central benzene ring and the ortho' hydrogen atoms of the peripheral aromatic units. These conformations are not favorable for a complexation of aromatic guests

• and the host–guest interactions must be able to equilibrate the previously described ortho–ortho' hindrance and to bring the aromatic rings of the caps to coplanar conformations. In this work, we decided to investigate a new cryptand in which this steric hindrance is removed. Thus, we changed the

• -triazine units in cryptand 2 exhibit a slight steric hindrance with the phenyl groups located at positions 2, 4 and 6 and thus, the reference triphenyltriazine aromatic platforms can adopt a planar structure which is favorable for the binding of aromatic guests such as anthracene, pyrene or 1,5

Synthesis of chiral 3-substituted 3-amino-2-oxindoles through enantioselective catalytic nucleophilic additions to isatin imines

• Hélène Pellissier

Beilstein J. Org. Chem. 2018, 14, 1349–1369, doi:10.3762/bjoc.14.114

• proton shift mediated by the organocatalyst occurred with the least steric hindrance between the quinuclidine moiety of the catalyst and the aromatic ring of the isatin imine. The same year, Chimni et al. reported organocatalyzed aza-Morita–Baylis–Hillman reactions of N-Boc-isatin imines 3 with

[3 + 2]-Cycloaddition reaction of sydnones with alkynes

• Veronika Hladíková,
• Jiří Váňa and
• Jiří Hanusek

Beilstein J. Org. Chem. 2018, 14, 1317–1348, doi:10.3762/bjoc.14.113

• cycloaddition completely fail [21][22] even after heating for 3 days in boiling xylene. This result was explained by the steric hindrance between the bulky substituents in the 4-position (iodine) and the substituents (Me, Br) in both ortho-positions of the adjacent 2,4,6-trisubstituted phenyl ring. All the

• , it can be concluded that any substituent in position 4 reduces the regioselectivity. The steric hindrance can also affect the ratio of the regioisomers formed. The classical example was described by Yeh et al. [75][76] who performed reactions of 3-(4-ethoxyphenyl)sydnone-4-carbonitrile with various

• -bistriflates) with two different dipoles from which one was 3-phenyl-4-(4-methoxyphenyl)sydnone (Scheme 14). The reason for the much better regioselectivity probably lies in the steric hindrance between the bulky t-BuMe2Si and 4-MeO-Ph groups. The in situ generation of arynes or six-membered cycloalkynes from

An overview of recent advances in duplex DNA recognition by small molecules

• Sayantan Bhaduri,
• Nihar Ranjan and
• Dev P. Arya

Beilstein J. Org. Chem. 2018, 14, 1051–1086, doi:10.3762/bjoc.14.93

• MGBs is their preference for narrow A·T-rich regions compared to G·C regions because (i) they can form hydrogen bonds to N3 of adenine and O2 of thymine in the A·T region; (ii) less steric hindrance in the A·T region in comparison to the G·C region due to the presence of an extra protruding C2-amino

2-Iodo-N-isopropyl-5-methoxybenzamide as a highly reactive and environmentally benign catalyst for alcohol oxidation

• Takayuki Yakura,
• Tomoya Fujiwara,
• Akihiro Yamada and
• Hisanori Nambu

Beilstein J. Org. Chem. 2018, 14, 971–978, doi:10.3762/bjoc.14.82

• -methoxyamide 25 was much slower than that with 13 and needed 23 h to complete (Table 1, entry 11). Although the ortho- and the para-methoxy groups should show a similar electronic effect on the iodine atom, the lower reactivity of 25 might be explained by the steric hindrance around the iodine atom of 25

Bromide-assisted chemoselective Heck reaction of 3-bromoindazoles under high-speed ball-milling conditions: synthesis of axitinib

• Jingbo Yu,
• Zikun Hong,
• Xinjie Yang,
• Yu Jiang,
• Zhijiang Jiang and
• Weike Su

Beilstein J. Org. Chem. 2018, 14, 786–795, doi:10.3762/bjoc.14.66

• disubstituted olefins 2d and 2e could participate in the reaction to deliver 3ao (67%), 3ad (26%) and 3ae (27%). Finally, the steric hindrance of styrene was examined. Larger steric hindrance (2m) led to lower yield (58%) as compared with 2k (89%) and 2l (88%). Application in API synthesis To demonstrate the