Development of the titanium–TADDOLate-catalyzed asymmetric fluorination of β-ketoesters

• Lukas Hintermann,
• Mauro Perseghini and
• Antonio Togni

Beilstein J. Org. Chem. 2011, 7, 1421–1435, doi:10.3762/bjoc.7.166

• steric requirement and aromatic stacking area was realized with 9-phenanthrenyl-TADDOL T4; this gave a maximal enantioselectivity with benzyl ester 10, rather than with the bulky ester 11. Presumably, the combined steric effects of substrate and ligand cannot exceed certain optimal limits. In the series

Highly efficient gold(I)-catalyzed Overman rearrangement in water

• Dong Xing and
• Dan Yang

Beilstein J. Org. Chem. 2011, 7, 781–785, doi:10.3762/bjoc.7.88

• , affording the desired product (2e) in 67% isolated yield (Table 2, entry 5). However, neither the substrates with phenyl (1f) nor dimethyl (1g) substituents at the C1 position gave the rearranged product (Table 2, entries 6 and 7), indicating that both electronic and steric effects at the C1 position play

Alkene selenenylation: A comprehensive analysis of relative reactivities, stereochemistry and asymmetric induction, and their comparisons with sulfenylation

• Vadim A. Soloshonok and
• Donna J. Nelson

Beilstein J. Org. Chem. 2011, 7, 744–758, doi:10.3762/bjoc.7.85

• the degree of substitution on C=C or upon substituent electronic effects. Electronic and steric effects influencing asymmetric induction, stereochemistry, regiochemistry, and relative reactivities in the addition of PhSeOTf to alkenes are compared and contrasted with those of PhSCl. Keywords: alkene

• selenenylation; asymmetric synthesis; calculations; electronic effects; regioselectivity; relative reactivities; steric effects; Introduction Electrophilic addition to alkenes is one of the most fundamental, generalized, and versatile methods for selective functionalization of hydrocarbons [1]. Despite recent

• in close proximity to Se, were demonstrated to influence the mechanism by resonance stabilization [63] or complexation [31][39]. Relative reactivities of various alkenes toward the addition of PhSeCl [55] have been reported, and the importance of steric effects in the reaction has been emphasized [27

Metathesis access to monocyclic iminocyclitol-based therapeutic agents

• Ileana Dragutan,
• Valerian Dragutan,
• Carmen Mitan,
• Hermanus C.M. Vosloo,
• Lionel Delaude and
• Albert Demonceau

Beilstein J. Org. Chem. 2011, 7, 699–716, doi:10.3762/bjoc.7.81

• , respectively), gave finally 135 with good stereoselectivity. This overall synthesis demonstrates rigorous control at every stage of both the steric configuration of the starting materials and the steric effects induced by substituents attached to the piperidine moiety. Related studies by Lebreton et al. [74

Brønsted acid-promoted azide–olefin [3 + 2] cycloadditions for the preparation of contiguous aminopolyols: The importance of disiloxane ring size to a diastereoselective, bidirectional approach to zwittermicin A

• Hubert Muchalski,
• Ki Bum Hong and
• Jeffrey N. Johnston

Beilstein J. Org. Chem. 2010, 6, 1206–1210, doi:10.3762/bjoc.6.138

• functionalization of the alkene of chiral allylic alcohols and ethers can be highly efficient, and the substrates are often easily accessible. The use of steric effects to achieve facial discrimination can be achieved by the introduction of a silyl group. Although several reports of diastereoselective azide–olefin

Recent advances in carbocupration of α-heterosubstituted alkynes

• Ahmad Basheer and
• Ilan Marek

Beilstein J. Org. Chem. 2010, 6, No. 77, doi:10.3762/bjoc.6.77

• is opposite to that predicted on the basis of electronic or steric effects alone [6][7]. Therefore acetylenic ether 10 possessing an additional chelating group was prepared and the regiochemistry of the carbometalation investigated as shown in Scheme 6 [8]. The addition of various organocopper

Synthesis, electronic properties and self-assembly on Au{111} of thiolated (oligo)phenothiazines

• Adam W. Franz,
• Svetlana Stoycheva,
• Michael Himmelhaus and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2010, 6, No. 72, doi:10.3762/bjoc.6.72

• the impact of steric effects on the adsorption kinetics and thus may lead to a more densely packed film. As a consequence, thiolated mono- and terphenothiazines 2 (n = 1, 3) and the dithiolated derivative 4 can be easily self-assembled to give stable monolayers on gold surfaces. This feature makes

The C–F bond as a conformational tool in organic and biological chemistry

• Luke Hunter

Beilstein J. Org. Chem. 2010, 6, No. 38, doi:10.3762/bjoc.6.38

• enantioselectivity of catalyst 52 is achieved solely through the Cγ-exo ring shape (assuming zero steric effects associated with the small fluorine atom). Overall, this work illustrates the great potential of using the C–F bond as a conformational tool in the development of new and improved organocatalysts. Multi

Molecular recognition of organic ammonium ions in solution using synthetic receptors

• Andreas Späth and
• Burkhard König

Beilstein J. Org. Chem. 2010, 6, No. 32, doi:10.3762/bjoc.6.32

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

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

• the “normal” 5-substituted isoxazoline is formed. Hence, the nitrodecene 123 gives rise to only the nine-membered carbocycle 125 upon reaction with phenyl isocyanate. The matching HOMO-LUMO interactions for such cycloadditions favour the formation of 126 but ring strain and transannular steric effects

Radical cascades using enantioenriched 7-azabenzonorbornenes and their applications in synthesis

• David M. Hodgson and
• Leonard H. Winning

Beilstein J. Org. Chem. 2008, 4, No. 38, doi:10.3762/bjoc.4.38

• through early transition states and, as such, steric effects are not usually significant [7]. Therefore, the lack of reactivity with 3-methyl-2-butenal could be due to the positive inductive effect of the terminal methyl groups rendering the β-position of the aldehyde less electrophilic. In an attempt to

Understanding the mechanism of Pd-catalyzed allylic substitution of the cyclic difluorinated carbonates

• Jun Xu,
• Xiao-Long Qiu and
• Feng-Ling Qing

Beilstein J. Org. Chem. 2008, 4, No. 18, doi:10.3762/bjoc.4.18

• should be temporarily generated once the compounds 1 or 4 were treated with palladium catalyst. Thus, α-substitution products should be afforded considering the steric effects. However, only γ-substitution products 2–3 and 5 were isolated in our case, which, in our opinion, resulted from the specific

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

• the terminal position of the double bond due to steric effects. On the basis of the above mentioned results, a proposed mechanism for the formation of 5a–h is outlined in Scheme 1. Trialkylphosphine catalysed Morita-Baylis-Hillman reaction is well studied by a number of groups [37][38][39]. Addition

Solvent- controlled regioselective protection of allyl- 4,6-benzylidene glucopyranosides

• Kerry Ann Ness and
• Marie E. Migaud

Beilstein J. Org. Chem. 2007, 3, No. 26, doi:10.1186/1860-5397-3-26

• allyl ether at the C1 position of the glucoside. It can be postulated that in THF, regioselectivity depends on the relative acidity of the secondary hydroxyl groups and the nucleophilicity of the resulting alkoxide. The acidity is modulated by intramolecular H-bonds while steric effects control the

Synthesis of 2,6-trans- disubstituted 5,6-dihydropyrans from (Z)-1,5-syn-endiols

• Eric M. Flamme and
• William R. Roush

Beilstein J. Org. Chem. 2005, 1, No. 7, doi:10.1186/1860-5397-1-7

• identical, steric effects on the activation of the two hydroxyl groups are eliminated. Therefore, the enantioselectivity of the ring closing step will depend only on the relative rates of the competing cyclization processes leading to 3a and ent-3a. Initial attempts at cyclization of 2a using Ph3P and

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

• (OsO4, TMEDA, CH2Cl2) conditions allow complementary diastereoselective functionalisation of the alkene of the (2R*,3R*) diastereoisomer. However, in the presence of a 6-substituent, the reaction is largely controlled by steric effects with both reagents. The most synthetically useful protocols were