Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations

• Rafia Siddiqui and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26

• temperature (Scheme 4) [94]. In their study, they observed that electron-donating groups provided better yields as compared to electron-withdrawing groups. The earlier reported methods for the synthesis of fluorenones, viz, Friedel–Craft acylations [95][96], oxidations of fluorenes [97][98], and Diels–Alder

Terpenes

• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2019, 15, 2966–2967, doi:10.3762/bjoc.15.292

• initially formed terpene hydrocarbons can subsequently be modified by enzymatic oxidations that often involve radical chemistry. The non-functionalised hydrocarbons are volatile and often exhibit interesting odour properties [3]. As a consequence, these compounds may act as chemical signals such as

Bacterial terpene biosynthesis: challenges and opportunities for pathway engineering

• Eric J. N. Helfrich,
• Geng-Min Lin,
• Christopher A. Voigt and
• Jon Clardy

Beilstein J. Org. Chem. 2019, 15, 2889–2906, doi:10.3762/bjoc.15.283

• challenging introduction of functional groups (mostly hydroxy groups) into nonactivated C–H bonds [46][105][106][107][108][109][110][111][112]. The absence of directing functional groups, however, renders these regioselective oxidations of nonactivated carbon atoms highly challenging, as the chemical

A review of asymmetric synthetic organic electrochemistry and electrocatalysis: concepts, applications, recent developments and future directions

• Munmun Ghosh,
• Valmik S. Shinde and
• Magnus Rueping

Beilstein J. Org. Chem. 2019, 15, 2710–2746, doi:10.3762/bjoc.15.264

• by a base (cyanomethyl anion) obtained from the galvanostatic reduction of acetonitrile/tetraethylammonium hexafluorophosphate (Scheme 57). Two years later, Lee and co-workers explored the efficacy of isoborneol-based chiral auxiliaries for asymmetric induction in intramolecular anodic oxidations of

Nanangenines: drimane sesquiterpenoids as the dominant metabolite cohort of a novel Australian fungus, Aspergillus nanangensis

• Heather J. Lacey,
• Cameron L. M. Gilchrist,
• Andrew Crombie,
• John A. Kalaitzis,
• Daniel Vuong,
• Peter J. Rutledge,
• Peter Turner,
• John I. Pitt,
• Ernest Lacey,
• Yit-Heng Chooi and
• Andrew M. Piggott

Beilstein J. Org. Chem. 2019, 15, 2631–2643, doi:10.3762/bjoc.15.256

• point, the pathway branches out to the different (iso)nananagenines via combinations of hydroxylation at C-1 (or not) and one or multiple oxidations at C-11 and C-12. The oxidations of methyl to alcohol and alcohol to aldehyde could be catalysed by one of the two P450 oxygenases, or the short-chain

Experimental and computational electrochemistry of quinazolinespirohexadienone molecular switches – differential electrochromic vs photochromic behavior

• Eric W. Webb,
• Jonathan P. Moerdyk,
• Kyndra B. Sluiter,
• Benjamin J. Pollock,
• Amy L. Speelman,
• Eugene J. Lynch,
• William F. Polik and
• Jason G. Gillmore

Beilstein J. Org. Chem. 2019, 15, 2473–2485, doi:10.3762/bjoc.15.240

• potential; on the oxidative return wave the subsequent oxidations of the LW dianion to its radical anion and then its neutral state are observed. Thus, in this unusual system, electrochromism proceeds by the same sort of spirocyclic ring-opening as the photochromic rearrangement but occurs from the radical

Synthesis of acremines A, B and F and studies on the bisacremines

• Nils Winter and
• Dirk Trauner

Beilstein J. Org. Chem. 2019, 15, 2271–2276, doi:10.3762/bjoc.15.219

• biogenetic precursor of acremines A (1) and B (2), we wanted to access these antifungal derivatives through selective oxidations. Indeed, treatment of 5 with IBX preferentially oxidized the C1-allylic alcohol, giving 1 in respectable yield. Prolonged treatment (9 h) of 5 with a large excess of IBX oxidized

An overview of the cycloaddition chemistry of fulvenes and emerging applications

• Ellen Swan,
• Kirsten Platts and
• Anton Blencowe

Beilstein J. Org. Chem. 2019, 15, 2113–2132, doi:10.3762/bjoc.15.209

• ], polyhalogenated cyclopentadienes (Scheme 15, reaction pathways (ii)) and 2-azadienes [152][172]. Regardless of the role of the fulvene moiety, the DAC is generally conducted in organic solvents at room temperature and under an inert atmosphere to prevent unwanted oxidations [24][55][94][114][150][152][159][166

Naphthalene diimides with improved solubility for visible light photoredox catalysis

• Barbara Reiß and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2019, 15, 2043–2051, doi:10.3762/bjoc.15.201

• reductions of cNDI 2 to the radical anion 2•− were observed at E½(2/2•−) = −1.06 V and to the dianion 22− at E½(2•−/22−) = −1.50 V and show the electronic effect of the two n-propylamino substituents. Additionally, two reversible oxidations were observed at E½(2•+/2) = +0.99 V and E½(22+/2•+) = +1.40 V which

Application of chiral 2-isoxazoline for the synthesis of syn-1,3-diol analogs

• Juanjuan Feng,
• Tianyu Li,
• Jiaxin Zhang and
• Peng Jiao

Beilstein J. Org. Chem. 2019, 15, 1840–1847, doi:10.3762/bjoc.15.179

• chromophore facilitating HPLC analysis. Afterwards, we tried oxidations once again. After removal of THP from 6, the resulting compound 6' was subjected to oxidation with various reagents (Scheme 4) [53][54][55]. The expected carboxylic acid or aldehyde was not observed, which further verified the intolerance

• methods using Claisen condensation. (b) Our new method using cycloaddition. Attempted oxidations of 4. Preparations of 16 and related syn-1,3-diol compounds. Attempted oxidations of 6'. Attempted selective protections of internal 1,3-hydroxy groups: (a) acetonizations of 1,3-diols; (b) removal of co

Metal-free mechanochemical oxidations in Ertalyte^® jars

• Andrea Porcheddu,
• Francesco Delogu,
• Lidia De Luca,
• Claudia Fattuoni and
• Evelina Colacino

Beilstein J. Org. Chem. 2019, 15, 1786–1794, doi:10.3762/bjoc.15.172

Transient and intermediate carbocations in ruthenium tetroxide oxidation of saturated rings

• Manuel Pedrón,
• Laura Legnani,
• Maria-Assunta Chiacchio,
• Pierluigi Caramella,
• Tomás Tejero and
• Pedro Merino

Beilstein J. Org. Chem. 2019, 15, 1552–1562, doi:10.3762/bjoc.15.158

• carbocation. In the case of pyrrolidines, the carbocation is completely stabilized as an energy minimum in the form of an iminium ion and the reaction takes place in two steps. Keywords: alkanes; carbocations; DFT; oxidations; ruthenium tetroxide; Introduction Ruthenium-catalyzed oxidations [1][2] and, in

• calculations are those indicated in Scheme 3. Results and Discussion We first studied the oxidations of cyclopentane (R1), tetrahydrofuran (R2) and tetrahydrothiophene (R3, Scheme 4). The geometries of all stationary points were optimized at the B3LYP-d3bj/Def2SVP level of theory in the gas phase and

• -methylpyrrolidine (R4) and N-benzylpyrrolidine R5 (Scheme 5). In the case of N-alkylpyrrolidines two regiosiomeric oxidations can take place at endo (cycle) and exo (N-chain) positions. We located the four transition structures TS4a and TS5a, corresponding to the endo series, and TS4b and TS5b, corresponding to the

Fluorine-containing substituents: metabolism of the α,α-difluoroethyl thioether motif

• Andrea Rodil,
• Alexandra M. Z. Slawin,
• Nawaf Al-Maharik,
• Ren Tomita and
• David O’Hagan

Beilstein J. Org. Chem. 2019, 15, 1441–1447, doi:10.3762/bjoc.15.144

• very active and outcompetes demethylation, however, that demethylation is significantly more active that the second oxidation of sulfoxides to sulfones. Incubation of naphthalene 5 with C. elegans, generated three new metabolites 11–13 which arose by oxidations at sulphur and hydroxylations of the

The LANCA three-component reaction to highly substituted β-ketoenamides – versatile intermediates for the synthesis of functionalized pyridine, pyrimidine, oxazole and quinoxaline derivatives

• Tilman Lechel,
• Roopender Kumar,
• Mrinal K. Bera,
• Reinhold Zimmer and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2019, 15, 655–678, doi:10.3762/bjoc.15.61

• oxidations of PM5, PM9, PM15 and PM19 furnishing aldehydes PM41, PM42, PM44 and PM48 are shown in Scheme 11 [33]. In case of the benzyl-substituted substrate PM5, the (probably faster) oxidation of the C-2 benzyl group could not be avoided and hence the dicarbonyl compound PM41 was isolated [50]. The formyl

• of pyrimidine derivatives PM through selenium dioxide oxidations of PM5, PM9, PM15 and PM19 leading to 4-formyl-substituted pyrimidines PM41, PM42, PM44 and PM48 and selected subsequent transformations (TosMIC = tosylmethyl isocyanide). Conversion of 2-vinyl-substituted pyrimidine PM7 into aldehyde

• PM61 and PM63, oxidations to formyl-substituted pyrimidines PM69 and PM71 and synthesis of nitrile PM72 (DMP = Dess–Martin periodinane). Synthesis of pyrimidinyl-substituted alkyne PM74 and conversion into furopyrimidine PM75 and Sonogashira reaction of PO3 with ethynylbenzene to pyrimidine N-oxide

Selective benzylic C–H monooxygenation mediated by iodine oxides

• Kelsey B. LaMartina,
• Haley K. Kuck,
• Linda S. Oglesbee,
• Asma Al-Odaini and
• Nicholas C. Boaz

Beilstein J. Org. Chem. 2019, 15, 602–609, doi:10.3762/bjoc.15.55

• hypervalent iodine oxidants to mediate benzylic C–H oxidation is one area experiencing a surge of interest [22][23][24][25][26][27][28][29][30][31][32][33]. Nonmetal-based benzylic oxidations have also been mediated by species including, but not limited to, electron deficient quinones, photoexcited organic

• oxidations occur via a radical pathway mediated in part by chlorine radicals [51]. While the chloride-iodate system was effective in the functionalization of light hydrocarbons and certain model compounds, it exhibited poor functional group tolerance. Oxidation of complex hydrocarbons led to a mixture of

• existence of a primary KIE suggests the cleavage of the benzylic C–H bond and formation of a benzylic radical during or prior to the rate determining step of the reaction. Such a mechanism is in line with other C–H oxidations catalyzed by NHPI [41][53][66][67]. It is proposed that formed aliphatic radicals

Synthesis of nonracemic hydroxyglutamic acids

• Dorota G. Piotrowska,
• Iwona E. Głowacka,
• Andrzej E. Wróblewski and
• Liwia Lubowiecka

Beilstein J. Org. Chem. 2019, 15, 236–255, doi:10.3762/bjoc.15.22

• )-2 and (2S,3S)-2 in several steps including hydroxymethyl to carboxyl oxidations (Scheme 2) [50]. N-Fmoc protection of the amino group in L-serine together with transformation of the carboxylic function into an orthoester allow for the racemization-free oxidation to aldehyde 10, which was immediately

Non-metal-templated approaches to bis(borane) derivatives of macrocyclic dibridgehead diphosphines via alkene metathesis

• Tobias Fiedler,
• Michał Barbasiewicz,
• Michael Stollenz and
• John A. Gladysz

Beilstein J. Org. Chem. 2018, 14, 2354–2365, doi:10.3762/bjoc.14.211

• . Oxidations that lead to the corresponding dibridgehead diphosphine dioxides (O=)P((CH2)n)3P(=O) have exhibited promise, but purification has been problematic [24]. Indeed, phosphine oxides are everyday precursors to phosphines, so we have considered various non-metal-templated routes to 2·2(=O), 3·2(=O), and

Tetrathiafulvalene – a redox-switchable building block to control motion in mechanically interlocked molecules

• Hendrik V. Schröder and
• Christoph A. Schalley

Beilstein J. Org. Chem. 2018, 14, 2163–2185, doi:10.3762/bjoc.14.190

• in rotaxane or catenane structures lead to a variety of different construction motifs. Its high stability in three different oxidation states and the change of multiple properties during these successive oxidations are ideally suited to drive molecular motions in MIMs. Additionally, the

Hypervalent iodine compounds for anti-Markovnikov-type iodo-oxyimidation of vinylarenes

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Mikhail A. Syroeshkin,
• Alexander A. Korlyukov,
• Pavel V. Dorovatovskii,
• Yan V. Zubavichus,
• Gennady I. Nikishin and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2018, 14, 2146–2155, doi:10.3762/bjoc.14.188

• radicals that is generated from an inexpensive N-hydroxyphthalimide (NHPI). This radical was used in various aerobic oxidations of bulk chemicals [18][19][43][44]. In the present work imide-N-oxyl radicals were used for the addition to the C=C bonds of styrenes with subsequent functionalization of the

Preparation and X-ray structure of 2-iodoxybenzenesulfonic acid (IBS) – a powerful hypervalent iodine(V) oxidant

• Irina A. Mironova,
• Pavel S. Postnikov,
• Rosa Y. Yusubova,
• Akira Yoshimura,
• Thomas Wirth,
• Viktor V. Zhdankin,
• Victor N. Nemykin and
• Mekhman S. Yusubov

Beilstein J. Org. Chem. 2018, 14, 1854–1858, doi:10.3762/bjoc.14.159

• to the respective carbonyl compounds with Oxone® (2KHSO5·KHSO4·K2SO4) in nitromethane, acetonitrile, or ethyl acetate [13]. Recent research has revealed the extreme activity of IBS as a catalyst in numerous other oxidations, such as: the oxidation of benzylic and alkane C–H bonds [14], the oxidation

Synthesis of spirocyclic scaffolds using hypervalent iodine reagents

• Fateh V. Singh,
• Priyanka B. Kole,
• Saeesh R. Mangaonkar and
• Samata E. Shetgaonkar

Beilstein J. Org. Chem. 2018, 14, 1778–1805, doi:10.3762/bjoc.14.152

• spirohexadiones from N-acyltyramines using iodine(III) reagent. After these reports, numerous hypervalent iodine-mediated spirocyclizations were investigated and phenolic oxidations of substrates have been explored for the construction of spirodienone motifs [21][64]. In 1993, Wipf and Kim [68] employed PIDA (15

A survey of chiral hypervalent iodine reagents in asymmetric synthesis

• Soumen Ghosh,
• Suman Pradhan and
• Indranil Chatterjee

Beilstein J. Org. Chem. 2018, 14, 1244–1262, doi:10.3762/bjoc.14.107

• asymmetric oxidations were examined in 20 mol % cetyltrimethylammonium bromide (CTAB) reversed micelles [25]. Interestingly, Varvoglis et al. synthesized another new class of a chiral reagent 3 using (+)-camphor sulfonic acids as the source of chirality [26] which was used by Chen et al. for the oxidation of

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

Selective carboxylation of reactive benzylic C–H bonds by a hypervalent iodine(III)/inorganic bromide oxidation system

• Toshifumi Dohi,
• Shohei Ueda,
• Kosuke Iwasaki,
• Yusuke Tsunoda,
• Koji Morimoto and
• Yasuyuki Kita

Beilstein J. Org. Chem. 2018, 14, 1087–1094, doi:10.3762/bjoc.14.94

• oxidations was recognized for displaying the new reactivities of hypervalent iodine reagents toward C(sp3)–H bonds [38][39]. By exploiting the radical behavior of trivalent iodine reagents discovered previously [40][41], the activation of trivalent iodine reagents, e.g., phenyliodine(III) diacetate (PIDA

• ), phenyliodine(III) bis(trifluoroacetate) (PIFA), and iodosobenzene, has since become a popular choice for benzylic oxidations, which further expanded the scope and availability of methods for direct C–H functionalization and several coupling reactions [42][43][44][45][46][47][48][49][50]. As such, we reported

• aqueous benzylic oxidations using polymeric iodosobenzene in the presence of inorganic bromide and montmorillonite-K10 [51]. In addition, a radical C–H activation strategy, using nonaqueous hypervalent iodine(III)/inorganic bromide systems that can work in organic solvents, was developed for the novel

2-Iodo-N-isopropyl-5-methoxybenzamide as a highly reactive and environmentally benign catalyst for alcohol oxidation

• Takayuki Yakura,
• Tomoya Fujiwara,
• Akihiro Yamada and
• Hisanori Nambu

Beilstein J. Org. Chem. 2018, 14, 971–978, doi:10.3762/bjoc.14.82

• 14a with 4-iodophenoxyacetic acid (23); the results showed excellent reactivity for phenol oxidations [60][61][62][63][64]. When 14a was oxidized with 23, the reaction was very slow and yielded only 23% of 15a and 75% of recovered 14a even after 48 h (Table 1, entry 9) [68]. Since the 5-methoxy

• reaction time than that with 13 (Table 2, entry 5). The primary alcohols 14g–k were converted into the corresponding carboxylic acids 26g–k in moderate to excellent yields (Table 2, entries 6–10). However, the reaction times of the oxidations of 14h, 14i, and 14k with 17 were similar to those involving 13