Halides as versatile anions in asymmetric anion-binding organocatalysis

• Lukas Schifferer,
• Martin Stinglhamer,
• Kirandeep Kaur and
• Olga García Macheño

Beilstein J. Org. Chem. 2021, 17, 2270–2286, doi:10.3762/bjoc.17.145

• performances as nucleophile precursors using a triazolium-amide chiral catalyst 34 [21] (Scheme 8a), as well as by Jacobsen in the desymmetrization of oxetanes 35 using TMSBr and squaramide 37 as catalyst [56] (Scheme 8b). For the latter, a more detailed mechanistic study was recently provided [57]. The

Lipophilicity trends upon fluorination of isopropyl, cyclopropyl and 3-oxetanyl groups

• Benjamin Jeffries,
• Zhong Wang,
• Robert I. Troup,
• Anaïs Goupille,
• Jean-Yves Le Questel,
• Charlene Fallan,
• James S. Scott,
• Elisabetta Chiarparin,
• Jérôme Graton and
• Bruno Linclau

Beilstein J. Org. Chem. 2020, 16, 2141–2150, doi:10.3762/bjoc.16.182

• ][20][21][22]. However, there is comparatively less precedence of lipophilicity comparisons between fluorinated isopropyl groups, cyclopropanes and oxetanes. Examples of bioactive compounds are given in Figure 2. During the optimization of the LpxC inhibitor 7a [23], it was shown that fluorination to

Selective preparation of tetrasubstituted fluoroalkenes by fluorine-directed oxetane ring-opening reactions

• Clément Q. Fontenelle,
• Thibault Thierry,
• Romain Laporte,
• Emmanuel Pfund and
• Thierry Lequeux

Beilstein J. Org. Chem. 2020, 16, 1936–1946, doi:10.3762/bjoc.16.160

• reaction of fluoroalkylidene-oxetanes was directed by the presence of the fluorine atom, enabling a two-step access to tetrasubstituted fluoroalkenes with excellent geometry control. Despite its small van der Waals radii electronic, rather than steric influences of the fluorine atom governed the ring

• envisioned an alternative approach starting from fluoroalkylidene-oxetane derivatives and to the end we have studied the selectivity of the oxetane ring-opening reaction (Figure 3). Results and Discussion The preparation of a series of fluoroalkylidene-oxetanes 1–3 was previously reported from 3-oxetanone

• through an olefination reaction with benzothiazoyl sulfones (Scheme 1) [22]. With these fluoroalkylidene-oxetanes in hands, we studied the selectivity of ring-opening reactions with heteroatom nucleophiles in order to access tetrasubstituted fluoroalkenes. A control of the geometry of these reactions

NHC-catalyzed enantioselective synthesis of β-trifluoromethyl-β-hydroxyamides

• Alyn T. Davies,
• Mark D. Greenhalgh,
• Alexandra M. Z. Slawin and
• Andrew D. Smith

Beilstein J. Org. Chem. 2020, 16, 1572–1578, doi:10.3762/bjoc.16.129

• [54]. We have previously applied these precursors in the NHC-catalyzed formal [2 + 2] cycloadditions between α-aroyloxyaldehydes and perfluoroalkyl-substituted ketones using NHC precatalyst 3 to produce polyfluorinated oxetanes and β-perfluoroalkyl-β-hydroxyamides after derivatization [55]. In this

Recent synthesis of thietanes

• Jiaxi Xu

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

• photochemical [2 + 2] cycloaddition of tert-butyl 2-(5-methyl-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)acetate (322) and thiobenzophenone (184a) was applied to prepare thietane 323 as a model compound for photolyses in a comparative flavin-induced cleavage study of oxetanes and thietanes [89] (Scheme 60). 2,5

• reagent for the nucleophilic ring expansion of three-membered heterocycles. It was successfully applied in the preparation of oxetanes and azetidines via the ring expansions of oxiranes [116][117][118] and aziridines [119][120]. However, both thiiranes and thietanes were less stable than the corresponding

Accelerating fragment-based library generation by coupling high-performance photoreactors with benchtop analysis

• Quentin Lefebvre,
• Christophe Salomé and
• Thomas C. Fessard

Beilstein J. Org. Chem. 2020, 16, 982–988, doi:10.3762/bjoc.16.87

• potential of the arylated product and promote oxidative decomposition. Several spirocyclic compounds with larger ring sizes could be coupled to 3-bromopyridine to give products 4c, 4d, 5a and 5b, provided that steric hindrance was not too high (see 5c). Surprisingly, oxetanes appear to be incompatible with

Aldehydes as powerful initiators for photochemical transformations

• Maria A. Theodoropoulou,
• Nikolaos F. Nikitas and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2020, 16, 833–857, doi:10.3762/bjoc.16.76

• Hanovia 450 W mercury arc [17]. If the reaction proceeded stereospecifically, cis-2-butene would have led to the formation of the oxetanes 75a and 75b, while trans-2-butene would have led to the oxetanes 75c and 75d (Scheme 19). It was suggested that the reaction proceeded through a long-lived biradical

• intermediate and rotation of the C3–C4 bond could in principle lead to all four possible oxetanes (Scheme 20). However, the formation of the oxetanes 75a and 75d was favored over that of the oxetanes 75b and 75c, probably because the intermediates for the products 75a and 75d contained the residue group and

• photosensitizers. Salicylaldehyde (68) forms an internal hydrogen bond. Olefin isomerization via energy transfer from a carbonyl compound. Mechanistic pathways for the Paterno–Büchi reaction. Isomeric oxetanes formed after photochemical addition of aryl aldehydes to 2-butenes. Rotation of the C3–C4 bond of the

Photophysics and photochemistry of NIR absorbers derived from cyanines: key to new technologies based on chemistry 4.0

• Bernd Strehmel,
• Christian Schmitz,
• Ceren Kütahya,
• Yulian Pang,
• Anke Drewitz and
• Heinz Mustroph

Beilstein J. Org. Chem. 2020, 16, 415–444, doi:10.3762/bjoc.16.40

• ]. Aziridines tolerate nucleophiles because chain growth requests the ammonium ion [93][94][95][96]. On the other hand, chain propagation includes the carbocation in the case of oxiranes and oxetanes [92]. More of interest can be seen absorbers, which do not follow such reaction routes. Scheme 7 depicts a

• photoproducts 33a–f did not permit successful run of cationic polymerization neither of oxiranes nor oxetanes. This became possible with the sensitizers 35–37 differing only with respect to their anion; that is [BF4]−, [PF6]− and [Al(O-t-C4F9)]− [6] after the first successful report of NIR-sensitized cationic

SO₂F₂-mediated transformation of 2'-hydroxyacetophenones to benzo-oxetes

• Revathi Lekkala,
• Ravindar Lekkala,
• Balakrishna Moku,
• K. P. Rakesh and
• Hua-Li Qin

Beilstein J. Org. Chem. 2019, 15, 976–980, doi:10.3762/bjoc.15.95

• catalyst-free novel and efficient methodology for the challenging synthesis of benzo-oxetes from 2'-hydroxyacetophenones mediated by sulfuryl fluoride (SO2F2) gas has been realized. The combination of 2'-hydroxyacetophenones and SO2F2 furnishes synthetically challenging benzo-oxetanes in moderate to

• excellent yields. The highlight of this work is the design and synthesis of strained four-membered oxete rings. Keywords: benzo-oxetes; 2'-hydroxyacetophenones; sulfuryl fluoride; Introduction Oxetanes are versatile elements in drug discovery and synthesis [1][2], and represent important moieties in some

• natural products and biological active molecules [3]. The synthesis and chemistry of oxetanes have been reviewed [1][2][4][5]. In medicinal chemistry, oxetanes have remained neglected units for many years since the first parent structure has been reported by Reboul in 1878 [6]. As strained cyclic ethers

Synthesis of five- and six-membered cyclic organic peroxides: Key transformations into peroxide ring-retaining products

• Alexander O. Terent'ev,
• Dmitry A. Borisov,
• Vera A. Vil’ and
• Valery M. Dembitsky

Beilstein J. Org. Chem. 2014, 10, 34–114, doi:10.3762/bjoc.10.6

• peroxides 47 are formed as by-products, which are desilylated during hydrolysis to give the unsaturated hydroperoxides 50 (Scheme 16, Table 7) [249]. 1,2-Dioxolanes can be produced from oxetanes 53a,b containing a double bond in the side chain according to a similar scheme. The first step afforded

• peroxide functional group. As in the above-considered studies, the intramolecular cyclization of ozonolysis products can be performed with the use of the hydroperoxide group provided that there is an appropriate electrophilic center. The reaction of oxetanes 60a,b with ozone in methanol produced 3-alkoxy

Formation of macrocyclic lactones in the Paternò–Büchi dimerization reaction

• Junya Arimura,
• Tsutomu Mizuta,
• Yoshikazu Hiraga and
• Manabu Abe

Beilstein J. Org. Chem. 2011, 7, 265–269, doi:10.3762/bjoc.7.35

• synthetically useful four-membered heterocyclic compounds, i.e., oxetanes. The Paternò–Büchi reaction of furan with a triplet carbonyl, such as n,π* triplet benzophenone, produces regioselectively 2-alkoxyoxetanes 2OX (Scheme 1). The regioselective formation is rationalized by the relative stability of the

Photocycloaddition of aromatic and aliphatic aldehydes to isoxazoles: Cycloaddition reactivity and stability studies

• Axel G. Griesbeck,
• Marco Franke,
• Jörg Neudörfl and
• Hidehiro Kotaka

Beilstein J. Org. Chem. 2011, 7, 127–134, doi:10.3762/bjoc.7.18

• isoxazoles are reported. The reactions lead solely to the exo-adducts with high regio- and diastereoselectivities. Ring methylation of the isoxazole substrates is crucial for high conversions and product stability. The 6-arylated bicyclic oxetanes 9a–9c were characterized by X-ray structure analyses and

• showed the highest thermal stabilities. All oxetanes formed from isoxazoles were highly acid-sensitive and also thermally unstable. Cleavage to the original substrates is dominant and the isoxazole derived oxetanes show type T photochromism. Keywords: isoxazoles; oxetanes; Paternò–Büchi reaction

• to alkenes (Paternò–Büchi reaction). This reaction is a superior route to oxetanes, which can be subsequently transformed into polyfunctionalized products [1]. With regards to the regio- and diastereoselectivity of the Paternò–Büchi reaction, recent experimental and computational studies have brought

Heavy atom effects in the Paternò–Büchi reaction of pyrimidine derivatives with 4,4’-disubstituted benzophenones

• Feng-Feng Kong,
• Jian-Bo Wang and
• Qin-Hua Song

Beilstein J. Org. Chem. 2011, 7, 113–118, doi:10.3762/bjoc.7.16

• (DMT) and 1,3-dimethyluracil (DMU) with benzophenone (1b) and some 4,4’-disubstituted derivatives (dimethoxy (1a), difluoro (1c), dichloro (1d), dibromo (1e) and dicyano benzophenone (1f)) that gives rise to two regioisomeric oxetanes, 2 and 3. The regioselectivity (the ratio of 2/3) decreased

• Paternò–Büchi reaction, spin-transition processes would be affected, and this may lead to interesting results. Abe et al. [14] investigated the effect of a sulfur atom on the stereoselective formation of oxetanes in Paternò–Büchi reaction of aromatic aldehydes with silyl O,S-ketene acetals to give trans-3

• detected for the reaction of α-deuterated propionaldehyde [15]. In this work, we have investigated the Paternò–Büchi reaction of 1,3-dimethylthymine (DMT) and 1,3-dimethyluracil (DMU) with benzophenone (1b) and its 4,4’-disubstituted derivatives 1a and 1c–1f with the formation of the regioisomeric oxetanes

Photocycloadditions and photorearrangements

• Axel G. Griesbeck

Beilstein J. Org. Chem. 2011, 7, 111–112, doi:10.3762/bjoc.7.15

• photocycloaddition, for example, is an important route to oxetanes, products that have recently gained increasing attention as building blocks in organic synthesis as well as in materials science [1]. Photochemical rearrangements are impressive reactions with regard to the generation of complexity: 1,2- and 1,3-acyl

Acid catalyzed cyclodimerization of 2,2-bis(trifluoromethyl)-4-alkoxy-oxetanes and -thietanes. Synthesis of 2,2,6,6-tetrakis(trifluoromethyl)-4,8-dialkoxy-1,5-dioxocanes and 3,3,7,7-tetrakis(trifluoromethyl)-9-oxa-2,6-dithia-bicyclo[3.3.1]nonane

• Viacheslav A. Petrov and
• Will Marshall

Beilstein J. Org. Chem. 2010, 6, No. 46, doi:10.3762/bjoc.6.46

• States 10.3762/bjoc.6.46 Abstract Treatment of 2,2-bis(trifluoromethyl)-4-R-oxetanes (R = C2H5O, n-C3H7O, n-C4H9O) with BF3·OEt2 in CH2Cl2 solvent results in spontaneous electrophilic [4 + 4] cyclodimerization with the formation of the corresponding 2,2,6,6-tetrakis(trifluoromethyl)-4,8-dialkoxy-1,5

• products. Clean and spontaneous reaction with alcohols is another interesting transformation of oxetanes described in this paper. The reaction leads to high yield formation of the corresponding acetals (CF3)2C(OH)CH2CH(OR)OR′. Structurally related 2,2-bis(trifluoromethyl)-4-R-thietanes (R = i-C3H7O, t

• was established by single crystal X-ray diffraction. Keywords: cyclodimerization; electrophilic [4 + 4] cyclodimerization; fluorinated oxetanes; fluorinated thietanes; reaction with alcohols; reaction with H2SO4; Introduction Polyfluorinated 2,2-bis(trifluoromethyl)-4-alkoxy-oxetanes and -thietanes