The Groebke–Blackburn–Bienaymé reaction in its maturity: innovation and improvements since its 21st birthday (2019–2023)

• Cristina Martini,
• Muhammad Idham Darussalam Mardjan and
• Andrea Basso

Beilstein J. Org. Chem. 2024, 20, 1839–1879, doi:10.3762/bjoc.20.162

• cyclophanyl-imidazole-based library of ligands. The synthesis of ligands based on the [2.2]paracyclophane (PCP) moiety, thanks to its structural features and inherent planar chirality upon selective substitution, has been recently reviewed by the same author [46]. Starting from 4-formylcyclophane 37, a GBB

Photochromic derivatives of indigo: historical overview of development, challenges and applications

• Gökhan Kaplan,
• Zeynel Seferoğlu and
• Daria V. Berdnikova

Beilstein J. Org. Chem. 2024, 20, 228–242, doi:10.3762/bjoc.20.23

• isomerization and photochemical (only for 13a) isomerization [46]. Compounds 13 showed intrinsic planar chirality and their enantiomers could be separated by HPLC. Notably, upon thermal and photochemical isomerization of these compounds, no Z-isomers were detected and only the racemization took place. Such

Germacrene B – a central intermediate in sesquiterpene biosynthesis

• Houchao Xu and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2023, 19, 186–203, doi:10.3762/bjoc.19.18

• photochemical E/Z isomerisation to 13 prior to [2 + 2] cycloaddition. Further photochemical products from 1 include 5, 15 that may be formed through a biradical mechanism, and rearranged 16 [51]. Germacrene B (1) has planar chirality (Scheme 4D), but recovery of the starting material from an incomplete

• ) Cyclisation of 1 to 9 and 10 upon treatment with alumina, B) conversion into (rac)-11 by treatment with diluted sulfuric acid in acetone, C) photochemical products from 1, and D) planar chirality of 1 and its derivative 17. Possible cyclisation reactions upon reprotonation of 1. A) Cyclisations to eudesmane

BINOL as a chiral element in mechanically interlocked molecules

• Matthias Krajnc and
• Jochen Niemeyer

Beilstein J. Org. Chem. 2022, 18, 508–523, doi:10.3762/bjoc.18.53

• planar chirality into at least one of the subcomponents. One of the most important chiral molecular frameworks in general is the 1,1'-binaphthyl-2,2'-diol unit (BINOL, see Figure 1). BINOL is an axially chiral molecule with a high configurational stability and a well-established synthetic chemistry

• and P isomers), similar to (S,S)-5 (see Figure 2). Secondly, the embedding of the DNP unit in the tetracationic cyclophane leads to an element of planar chirality (Rp and Sp isomers). Thus, for each configuration of BINOL, four different diastereoisomers are possible. However, for these specific

• rotaxanes, the helicity is predetermined by the planar chirality (based on the underlying macrocycle–macrocycle interactions), so that only two diastereoisomers remain for a given BINOL configuration (e.g., (R)-(Rp) and (R)-(Sp) in case of (R)-BINOL). In contrast to the axial chirality of the BINOL unit

New advances in asymmetric organocatalysis

• Radovan Šebesta

Beilstein J. Org. Chem. 2022, 18, 240–242, doi:10.3762/bjoc.18.28

• Waser employed an isothiourea catalyst for esterification-mediated kinetic resolution of paracyclophane derivatives with planar chirality [19]. Parida and Pan showed that a Michael reaction coupled with an acyl transfer reaction between α-nitroketones and 4-arylidenepyrrolidine-2,3-diones can produce a

Breaking paracyclophane: the unexpected formation of non-symmetric disubstituted nitro[2.2]metaparacyclophanes

• Suraj Patel,
• Tyson N. Dais,
• Paul G. Plieger and
• Gareth J. Rowlands

Beilstein J. Org. Chem. 2021, 17, 1518–1526, doi:10.3762/bjoc.17.109

• nitronium ion must occur anti to the para ring of the cyclophane. Approach from the opposite face is blocked by the lower deck. Once oxidation has occurred conformational flipping of the meta deck is impossible and the planar chirality is locked [39]. It is possible that more cyclohexadienone cyclophane 6

Chiral isothiourea-catalyzed kinetic resolution of 4-hydroxy[2.2]paracyclophane

• David Weinzierl and
• Mario Waser

Beilstein J. Org. Chem. 2021, 17, 800–804, doi:10.3762/bjoc.17.68

• ; planar chirality; Introduction Substituted [2.2]paracyclophanes are fascinating planar chiral molecules [1][2][3][4][5][6][7][8][9][10][11][12] which have been systematically investigated since Brown and Farthing discovered the formation of the unsubstituted and achiral parent [2.2]paracyclophane (1

Synthesis, enantioseparation and photophysical properties of planar-chiral pillar[5]arene derivatives bearing fluorophore fragments

• Guojuan Li,
• Chunying Fan,
• Guo Cheng,
• Wanhua Wu and
• Cheng Yang

Beilstein J. Org. Chem. 2019, 15, 1601–1611, doi:10.3762/bjoc.15.164

• that differs from the common macrocycles is the planar chirality resulting from the different orientations of the alkoxy substituents on the rims. Theoretically, eight conformers can be formed including diastereomeric ones: (Sp,Sp,Sp,Sp,Sp), (Rp,Sp,Sp,Sp,Sp), (Rp,Rp,Sp,Sp,Sp), (Rp,Sp,Rp,Sp,Sp) and

Determination of the absolute stereostructure of a cyclic azobenzene from the crystal structure of the precursor containing a heavy element

• Reji Thomas and
• Nobuyuki Tamaoki

Beilstein J. Org. Chem. 2016, 12, 2211–2215, doi:10.3762/bjoc.12.212

• Z-state of azobenzene, (iii) chiral in both states of the azobenzene unit. We have explored the property of planar chirality of these molecules and carried out the optical resolution to demonstrate various properties such as molecular brakes, chiroptical switches and chirality sensors for light and

• polygonal finger print texture [45]. Molecule (E)-1 contains a 2,6-dibromo-1,5-dihydroxynaphthalene part linked to an azobenzene unit through bismethylene spacers. The constricted rotation of the naphthalene unit in the cyclic structure gives planar chirality to this molecule with separable enantiomers. The

[2.2]Paracyclophane derivatives containing tetrathiafulvalene moieties

• Laura G. Sarbu,
• Lucian G. Bahrin,
• Peter G. Jones,
• Lucian M. Birsa and
• Henning Hopf

Beilstein J. Org. Chem. 2015, 11, 1917–1921, doi:10.3762/bjoc.11.207

• a mixture of inseparable isomeric tetrathiafulvalenes 7 in 17% yield. Since compound 6 already exhibits planar chirality (racemate Rp/Sp), the theoretical number of stereoisomers of the tetrathiafulvalene 7 should be six as follows: cis-(Sp,Sp) with cis-(Rp,Rp) and trans-(Sp,Sp) with trans-(Rp,Rp

Inherently chiral calix[4]arenes via oxazoline directed ortholithiation: synthesis and probe of chiral space

• Simon A. Herbert,
• Laura J. van Laeren,
• Dominic C. Castell and
• Gareth E. Arnott

Beilstein J. Org. Chem. 2014, 10, 2751–2755, doi:10.3762/bjoc.10.291

• . Currently we are looking at different catalytic systems, also based on the planar chiral ferrocenes, but which have shown the planar chirality of the ferrocene to be essential in determining the selectivity and/or efficiency of the transformations. Our ultimate aim is to establish whether or not the

De novo macrolide–glycolipid macrolactone hybrids: Synthesis, structure and antibiotic activity of carbohydrate-fused macrocycles

• Richard T. Desmond,
• Anniefer N. Magpusao,
• Chris Lorenc,
• Jeremy B. Alverson,
• Nigel Priestley and
• Mark W. Peczuh

Beilstein J. Org. Chem. 2014, 10, 2215–2221, doi:10.3762/bjoc.10.229

• backbone of the macrocycle whose chirality is dictated by the absolute configuration of the C4 stereogenic center. The topology is a defining feature of this family of [13]-macrodiolides. By virtue of the planar chirality, [13]-macrodiolides such as 3 have an axis of chirality associated with them. We were

Enantioselective synthesis of planar chiral ferrocenes via palladium-catalyzed annulation with diarylethynes

• Yan-Chao Shi,
• Rong-Fei Yang,
• De-Wei Gao and
• Shu-Li You

Beilstein J. Org. Chem. 2013, 9, 1891–1896, doi:10.3762/bjoc.9.222

• Road, BDA, Beijing, 100176, China 10.3762/bjoc.9.222 Abstract When Boc-L-Val-OH was used as a ligand for the enantioselective Pd(II)-catalyzed annulation of N,N-substituted aminomethyl ferrocene derivatives with diarylethynes, ferrocenes with planar chirality could be achieved with excellent

• enantioselectivity (up to 99% ee). Keywords: annulation; asymmetric catalysis; C–H activation; ferrocene; palladium; planar chirality; Introduction Chiral ferrocene derivatives have been widely applied to asymmetric catalysis, materials science, biomedical research, etc. [1][2][3][4]. Particularly, ferrocenes with

• planar chirality are applied as efficient ligands or catalysts in asymmetric catalysis [5][6][7][8][9][10][11][12][13][14][15]. However, the typical method for introduction of planar chirality in the ferrrocene backbone is still utilizing the chiral auxiliaries strategy [16][17][18][19][20][21]. Snieckus

Rh(III)-catalyzed directed C–H bond amidation of ferrocenes with isocyanates

• Satoshi Takebayashi,
• Tsubasa Shizuno,
• Takashi Otani and
• Takanori Shibata

Beilstein J. Org. Chem. 2012, 8, 1844–1848, doi:10.3762/bjoc.8.212

• reactivity. The absolute configuration of planar chirality in 3c was determined to be S by X-ray crystallography (Figure 1). The absolute configuration is consistent with the previous report of diastereoselective ortho-lithiation of 1b [27]. Conclusion In conclusion, a Cp*Rh(III)-catalyzed reaction between

Synthesis and structure of tricarbonyl(η⁶-arene)chromium complexes of phenyl and benzyl D-glycopyranosides

• Thomas Ziegler and
• Ulrich Heber

Beilstein J. Org. Chem. 2012, 8, 1059–1070, doi:10.3762/bjoc.8.118

• to the fact that the tricarbonylchromium ligand stabilizes both benzylic and homo-benzylic carbenium ions and carbanions [5][6]. Asymmetric ortho- or meta-substituted tricarbonyl(η6-arene)chromium compounds display planar chirality, which, in turn, makes these chiral complexes attractive catalysts

Carbamate-directed benzylic lithiation for the diastereo- and enantioselective synthesis of diaryl ether atropisomers

• Abigail Page and
• Jonathan Clayden

Beilstein J. Org. Chem. 2011, 7, 1327–1333, doi:10.3762/bjoc.7.156

• -dimethylbenzene) with the aim of generating an atropisomeric product in enantiomerically enriched form (Scheme 1) [2]. Enantioselective lithiation has since then commonly been used to generate axial or planar chirality [3], in many cases by desymmetrising deprotonation of a functionalised aromatic system. The

Use of mixed Li/K metal TMP amide (LiNK chemistry) for the synthesis of [2.2]metacyclophanes

• Marco Blangetti,
• Patricia Fleming and
• Donal F. O'Shea

Beilstein J. Org. Chem. 2011, 7, 1249–1254, doi:10.3762/bjoc.7.145

• oxidative coupling with 1,2-dibromoethane. The synthetic ease of this approach compares favourably with previously reported methods and allows for ready access to potentially useful planar chiral derivatives. Keywords: benzylic metalation; LiNK chemistry; [2.2]metacyclophane; oxidative coupling; planar

• chirality; Introduction While direct metalation reactions are an essential contribution to the repertoire of modern synthetic methods, an underlying and often underestimated challenge remains in the achievement of predictable selective metalations of substrates that offer several potential sites of

Enantiospecific synthesis of [2.2]paracyclophane- 4-thiol and derivatives

• Gareth J. Rowlands and
• Richard J. Seacome

Beilstein J. Org. Chem. 2009, 5, No. 9, doi:10.3762/bjoc.5.9

• range of disubstituted derivatives [33]. The basis of the strategy is the stereospecific introduction of a sulfoxide to [2.2]paracyclophane to give readily separable diastereoisomers, thus resolving the planar chirality [34]. The sulfoxide moiety is used to direct further elaboration of the [2.2

• success of this strategy was the resolution of the planar chirality of [2.2]paracyclophane by incorporation of the tert-butylsulfinyl moiety to give the diastereoisomers (Sp,RS)-5 and (Rp,RS)-5. Standard iron-catalysed bromination of 1 gave (±)-4-bromo[2.2]paracyclophane 3 in good yield [35][36]. Halogen

• the facile resolution of the planar chirality. The assignment of configuration is based on a combination of X-ray studies [33][38], formation of all stereoisomers and analogy to our previous tolylsulfinyl chemistry [31][39]. Unlike the previously prepared 4-tolylsulfinyl[2.2]paracyclophane [31