Strategies to access the [5-8] bicyclic core encountered in the sesquiterpene, diterpene and sesterterpene series

• Cécile Alleman,
• Charlène Gadais,
• Laurent Legentil and
• François-Hugues Porée

Beilstein J. Org. Chem. 2023, 19, 245–281, doi:10.3762/bjoc.19.23

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

• Guido Gambacorta,
• James S. Sharley and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2021, 17, 1181–1312, doi:10.3762/bjoc.17.90

Insight into functionalized-macrocycles-guided supramolecular photocatalysis

• Minzan Zuo,
• Krishnasamy Velmurugan,
• Kaiya Wang,
• Xueqi Tian and
• Xiao-Yu Hu

Beilstein J. Org. Chem. 2021, 17, 139–155, doi:10.3762/bjoc.17.15

• of functional photocatalytic systems [16][17]. The diversity of crown ether-based photocatalytic reactions is relatively low, involving mainly photocycloaddition reactions. Saltiel and co-workers reported the regiospecific intermolecular [2 + 2]-photocycloaddition based on a supramolecular assembly

• issues in industrial engineering. Chemical structures of representative macrocycles. Ba2+-induced intermolecular [2 + 2]-photocycloaddition of crown ether-functionalized substrates 1 and 2 to form cycloadduct 3. Republished with permission of The Royal Society of Chemistry from [18] (“Supramolecular

Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

• that is trapped intermolecularly by N-hydroxycarbamates 152 (Scheme 21b) [71]. Bach et al. has recently reported a bifunctional catalyst 154, which contains both a photoactive thioxanthone unit and a CPA (Scheme 22) [72]. They have applied this photocatalyst to the [2 + 2] photocycloaddition of

• enantioselectivity (85:15 er). Photocatalyst 174 was next applied to the formal [2 + 2] photocycloaddition of quinolones 181, which is analogous to the reaction developed by Krische et al. in Scheme 25. Similarly, the mechanism that is proposed proceeds through complex 182 that can be photosensitised into its

• amount of background reaction and the more rigid xanthone structure acting as a superior stereo-directing group. Further variation to a thioxanthone unit 185, which has a lower triplet energy (ET = 2.7 eV), was used to investigate a similar [2 + 2] photocycloaddition, giving comparable yields and

Chan–Evans–Lam N1-(het)arylation and N1-alkеnylation of 4-fluoroalkylpyrimidin-2(1H)-ones

• Viktor M. Tkachuk,
• Oleh O. Lukianov,
• Mykhailo V. Vovk,
• Isabelle Gillaizeau and
• Volodymyr A. Sukach

Beilstein J. Org. Chem. 2020, 16, 2304–2313, doi:10.3762/bjoc.16.191

• analogous enamides [57], the facile [2 + 2] photocycloaddition process likely occurred due to favorable orientation of the interacting molecules and close contacts between alkene carbon atoms in the crystal structure. Consequently, the synthesis of product 5c was performed in darkness. N1-Styryl-substituted

Recent synthesis of thietanes

• Jiaxi Xu

Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116

• were obtained via a ring cleavage of the thietanes, that had formed in the [2 + 2] photocycloaddition of the thiocarbonyl moiety and the olefin. However, the reaction of 1,3,3-trimethylindoline-2-thione (300) and isobutene (215c) afforded the corresponding spiroindoline-thietane derivative 301 [80

Synthesis of esters of diaminotruxillic bis-amino acids by Pd-mediated photocycloaddition of analogs of the Kaede protein chromophore

• Esteban P. Urriolabeitia,
• Pablo Sánchez,
• Alexandra Pop,
• Cristian Silvestru,
• Eduardo Laga,
• Ana I. Jiménez and
• Carlos Cativiela

Beilstein J. Org. Chem. 2020, 16, 1111–1123, doi:10.3762/bjoc.16.98

• -face arrangement, which is optimal for their [2 + 2] photocycloaddition. Irradiation of dimers 3 in CH2Cl2 solution with blue light (465 nm) promoted the chemo- and stereoselective [2 + 2] photocycloaddition of the exocyclic C=C bonds and the formation of cyclobutane-containing ortho-palladated

• date [16][17][18]. The properties outlined above highlight the importance of the wide scope of applications of this set of cyclobutanes. Despite their importance, access to most of these compounds mainly relies in the well-known [2 + 2] photocycloaddition of olefins [19]. Unfortunately, the synthesis

• of truxillic or diaminotruxillic derivatives is far from being a highly efficient, selective and general process. Two different cases are usually found in the literature: (a) the direct [2 + 2] photocycloaddition of the corresponding olefins takes place, but shows poor efficiency (long reaction times

Reversible photoswitching of the DNA-binding properties of styrylquinolizinium derivatives through photochromic [2 + 2] cycloaddition and cycloreversion

• Sarah Kölsch,
• Heiko Ihmels,
• Jochen Mattay,
• Norbert Sewald and
• Brian O. Patrick

Beilstein J. Org. Chem. 2020, 16, 111–124, doi:10.3762/bjoc.16.13

• methoxy-substituted styrylquinolizinium derivatives form the corresponding syn head-to-tail cyclobutanes in a selective [2 + 2] photocycloaddition, as revealed by X-ray diffraction analysis of the reaction products. These photodimers bind to DNA only weakly by outside-edge association, but they release

• deactivation of a stilbene tyrosine kinase inhibitor by a [2 + 2] photocycloaddition [59]. As the quinolizinium ion has been established as a versatile platform for the development of DNA intercalators [60], we identified styryl-substituted quinolizinium derivatives as a promising basis for the search for

• shown that appropriately substituted styrylquinolizinium derivatives constitute a new class of photoswitchable DNA ligands. It was shown that these ligands bind to duplex DNA mainly by intercalation and that their syn head-to-tail photodimers, obtained by selective [2 + 2] photocycloaddition, bind to

Spiro annulation of cage polycycles via Grignard reaction and ring-closing metathesis as key steps

• Sambasivarao Kotha,
• Mohammad Saifuddin,
• Rashid Ali and
• Gaddamedi Sreevani

Beilstein J. Org. Chem. 2015, 11, 1367–1372, doi:10.3762/bjoc.11.147

• Claisen rearrangement and RCM as key steps [21][30]. Here, we have prepared the cage dione 10 by the known route involving two atom-economic protocols such as Diels–Alder reaction and [2 + 2] photocycloaddition [42][43][44][45] (Scheme 1). Later, the hexacyclic cage dione 10 was subjected to a Grignard

Selected synthetic strategies to cyclophanes

• Sambasivarao Kotha,
• Mukesh E. Shirbhate and
• Gopalkrushna T. Waghule

Beilstein J. Org. Chem. 2015, 11, 1274–1331, doi:10.3762/bjoc.11.142

• treated with LAH to generate diol 266 (72–92%). The dehydration of diol 266 with pyridinium p-toluenesulfonate in benzene gave diolefin 267. [2 + 2] Photocycloaddition of diolefin 267 was carried out by irradiation with a 400 W high-pressure Hg lamp (Pyrex filter) in benzene for 26–92 h. After evaporation

Synthesis of carbohydrate-scaffolded thymine glycoconjugates to organize multivalency

• Anna K. Ciuk and
• Thisbe K. Lindhorst

Beilstein J. Org. Chem. 2015, 11, 668–674, doi:10.3762/bjoc.11.75

• dimerized by [2 + 2] photocycloaddition. Thus, thymine functions as a control element that allows to restrict the conformational flexibility of the scaffolded sugar ligands and thus to “organize” multivalency. With this work we add a parameter to multivalency studies additional to valency. Keywords: [2 + 2

• appropriate carbohydrate conjugation the same molecular architecture could be applied for organization of a divalent glycoconjugate (Figure 1B). We selected thymine as a photocontrollable element as it can undergo [2 + 2] photocycloaddition upon irradiation with light of hν ≥ 290 nm [5][9][10]. Furthermore

• used as scaffold molecule, and α-D-mannosides as specific carbohydrate ligands for the fabrication of the envisaged divalent glycoconjugate (Figure 1C). In the following, we report the synthesis of the divalent glycoconjugates outlined in Figure 1 and their [2 + 2] photocycloaddition. Results and

Articulated rods – a novel class of molecular rods based on oligospiroketals (OSK)

• Pablo Wessig,
• Roswitha Merkel and
• Peter Müller

Beilstein J. Org. Chem. 2015, 11, 74–84, doi:10.3762/bjoc.11.11

• distance dependent change in the fluorescence spectrum. Furthermore, we were interested in functional groups in the terminal positions of the ARs enabling reversible switching between the two states. This was supposed to be accomplished both by [2 + 2] photocycloaddition of derivatives of cinnamic acid and

Design and synthesis of novel bis-annulated caged polycycles via ring-closing metathesis: pushpakenediol

• Sambasivarao Kotha and
• Mirtunjay Kumar Dipak

Beilstein J. Org. Chem. 2014, 10, 2664–2670, doi:10.3762/bjoc.10.280

• ] cycloaddition strategies, which involve the DA reaction of 2,5-dialkyl-1,4-benzoquinone 10 and 1,3-cyclopentadiene (9) followed by the formation of the cyclobutane ring through a [2 + 2] photocycloaddition reaction (Figure 2). Later on, one can introduce two allyl groups by using traditional carbonyl chemistry

Flow photochemistry: Old light through new windows

• Jonathan P. Knowles,
• Luke D. Elliott and
• Kevin I. Booker-Milburn

Beilstein J. Org. Chem. 2012, 8, 2025–2052, doi:10.3762/bjoc.8.229

• competitive [29]. In a similar [2 + 2] photocycloaddition (Scheme 5), the authors demonstrated that by extending the chain length by one carbon, the 4,6-fused ring system 14 could be formed, albeit with some formation of regioisomer 15. In this instance the batch reaction gave slightly better selectivity than

The arene–alkene photocycloaddition

• Ursula Streit and
• Christian G. Bochet

Beilstein J. Org. Chem. 2011, 7, 525–542, doi:10.3762/bjoc.7.61

• known representatives are undoubtedly the [2 + 2] photocycloaddition, forming either cyclobutanes or four-membered heterocycles (as in the Paternò–Büchi reaction), whilst excited-state [4 + 4] cycloadditions can also occur to afford cyclooctadiene compounds. On the other hand, the well-known thermal [4

• slightly different irradiation conditions. A very unconventional [2 + 2] photocycloaddition to afford caged polycyclic structures has been recently described (Scheme 29) [89][90]. By attaching the double bond very close to the aromatic moiety, the photocycloaddition leads to the desired cage compound in