Revisiting the bromination of 3β-hydroxycholest-5-ene with CBr₄/PPh₃ and the subsequent azidolysis of the resulting bromide, disparity in stereochemical behavior

• Christian Schumacher,
• Jas S. Ward,
• Kari Rissanen,
• Carsten Bolm and
• Mohamed Ramadan El Sayed Aly

Beilstein J. Org. Chem. 2023, 19, 91–99, doi:10.3762/bjoc.19.9

• [13][14]. In similar work, Peterson and co-workers reported several examples of such stereoretentive conversions of cholesterol, which provided the corresponding 3β-halo- and 3β-azido-5-cholesterenes in high yields [12]. The cholesterol mesylate was the most effective intermediate, and the

Progress in metathesis chemistry

• Karol Grela and
• Anna Kajetanowicz

Beilstein J. Org. Chem. 2019, 15, 2765–2766, doi:10.3762/bjoc.15.267

• by Kotha et al. [4], on artificial metalloproteins by Okuda et al. [5], on stereoretentive ruthenium dithiolate catalysts by Mauduit et al. [6], on unsymmetrical NHC ligands by Grisi et al. [7], on polymers by Kudryavtsev [8] and on polyhedral oligomeric silsesquioxanes by Pietraszuk et al. [9

Alkylation of lithiated dimethyl tartrate acetonide with unactivated alkyl halides and application to an asymmetric synthesis of the 2,8-dioxabicyclo[3.2.1]octane core of squalestatins/zaragozic acids

• Herman O. Sintim,
• Hamad H. Al Mamari,
• Hasanain A. A. Almohseni,
• Younes Fegheh-Hassanpour and
• David M. Hodgson

Beilstein J. Org. Chem. 2019, 15, 1194–1202, doi:10.3762/bjoc.15.116

• LDA and reaction at −78 °C during 12–72 h with a range of alkyl halides, including non-activated substrates, to give single diastereomers (at the acetonide) of monoalkylated tartrates 17, 24, 33a–f, 38a,b, 41 of R,R-configuration, i.e., a stereoretentive process (13–78% yields). Separable trans

• subsequently those of Nagano [27] and of Li [28] for allylations, i.e., stereoretentive (contrasteric) alkylation. As noted above, Seebach recorded 97:3 er (by NMR using a chiral shift reagent) for a benzylated tartrate [18]; in the present case, chiral HPLC comparison of 17 with the corresponding adduct from

• stereoretentive alkylation, then direct access to the stereochemistry present in the majority of these natural products is not possible. Nevertheless, a couple of isolated examples in the Chinese chemical literature from the late 1980s indicated that subsequent base-induced epimerisation of monoalkylated (p

A tutorial review of stereoretentive olefin metathesis based on ruthenium dithiolate catalysts

• Daniel S. Müller,
• Olivier Baslé and
• Marc Mauduit

Beilstein J. Org. Chem. 2018, 14, 2999–3010, doi:10.3762/bjoc.14.279

• Daniel S. Muller Olivier Basle Marc Mauduit Univ. Rennes, Ecole Nationale Supérieure de Chimie de Rennes, CNRS, ISCR – UMR 6226, F-35000 Rennes, France 10.3762/bjoc.14.279 Abstract Stereoretentive olefin metathesis based on ruthenium dithiolate complexes has become a very active field of research

• dithiolate catalysts in a logic manner, thus providing an "operators handbook" for chemists who wish to apply this methodology in synthesis. Keywords: catalysis; olefin metathesis; ruthenium; stereoretentive; Review 1 Catalyst discovery and structure optimization from 2013–2018 In stereoretentive

• group showed that Ru dithiolate catalysts are not stereoselective but stereoretentive catalysts [3]. Given the significant difference in geometry of Z- and E-alkenes it is obvious that each type of alkene requires a different catalyst (Figure 1). In both the Z- and E-stereoretentive processes, Ru-3

Strategies toward protecting group-free glycosylation through selective activation of the anomeric center

• A. Michael Downey and
• Michal Hocek

Beilstein J. Org. Chem. 2017, 13, 1239–1279, doi:10.3762/bjoc.13.123

• perfectly stereospecific as complete retention of the stereochemistry was observed in all cases. The initial scope used a benzyl-protected glucosylstannane as the donor and a series of aryl halides as acceptors and in all instances the reaction was stereoretentive (Scheme 19) although a mechanistic

α,β-Aziridinylphosphonates by lithium amide-induced phosphonyl migration from nitrogen to carbon in terminal aziridines

• David. M. Hodgson and
• Zhaoqing Xu

Beilstein J. Org. Chem. 2010, 6, 978–983, doi:10.3762/bjoc.6.110

• phosphonyl rearrangements (8→9, Scheme 2) were developed by Hammerschmidt and Hanbauer [21], and a stereoretentive N- to C-[1,2]-shift in an α-lithiated pyrrole involving a chiral tert-butyl(phenyl)phosphinyl group has been reported [22]. With regard to previous anion-induced N- to C-1,2-shifts in aziridines

Shelf-stable electrophilic trifluoromethylating reagents: A brief historical perspective

• Norio Shibata,
• Andrej Matsnev and
• Dominique Cahard

Beilstein J. Org. Chem. 2010, 6, No. 65, doi:10.3762/bjoc.6.65

• stereoretentive CF3 transfer. High enantioselectivities in the range 93–97% were measured for the corresponding alcohols because of post-reaction racemization of aldehydes. Although the scope of this asymmetric reaction is limited to aldehydes, the level of enantioselectivity is superior to that obtained in the