Bipyrrole boomerangs via Pd-mediated tandem cyclization–oxygenation. Controlling reaction selectivity and electronic properties

• Liliia Moshniaha,
• Marika Żyła-Karwowska,
• Joanna Cybińska,
• Piotr J. Chmielewski,
• Ludovic Favereau and
• Marcin Stępień

Beilstein J. Org. Chem. 2020, 16, 895–903, doi:10.3762/bjoc.16.81

• activation, and a double α-oxygenation. The latter reaction can be partly suppressed for the least reactive systems, providing access to α-unsubstituted boomerangs for the first time. These “α-free” systems are highly efficient fluorophores, with emission quantum yields exceeding 80% in toluene. Preliminary

• stoichiometric oxidant. The scope of such Pd(II)-induced couplings was further developed into tandem processes involving consecutive cyclization of substituents (dcTTEE) and oxygenation of pyrrolic α-positions to form lactams cNDA1O and cNMI1O. The mechanism of those transformations was subsequently explored

• using NMR spectroscopy and DFT calculations [33]. In particular, the unprecedented double α-oxygenation of bipyrroles was shown to occur through stepwise acetoxylation, which we found to compete with α–α oligomerization. These new bipyrrole boomerangs exhibited enhanced fluorescence with Φfl values of

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

• derivatives using the cumene process or single-step oxygenation suffers from poor yields, high reaction temperatures, and high-energy UV irradiation conditions [155][156]. To overcome this, in 2012, Fukuzumi and co-workers used 3-cyano-1-methylquinolinium perchlorate (8) as a photoredox catalyst for the

• benzene are difficult to oxidize with nonphotochemical processes, whereas with photoredox catalyst 5 and TBN in the presence of oxygen, benzene can be easily be oxidized (Scheme 19) [158]. Remarkably, photoredox catalyst 5 offered a one-step oxygenation of arenes to phenol with high quantum yields. It was

Thermal stability of N-heterocycle-stabilized iodanes – a systematic investigation

• Andreas Boelke,
• Yulia A. Vlasenko,
• Mekhman S. Yusubov,
• Boris J. Nachtsheim and
• Pavel S. Postnikov

Beilstein J. Org. Chem. 2019, 15, 2311–2318, doi:10.3762/bjoc.15.223

• stability with reactivity in a model oxygenation. Keywords: differential scanning calorimetry; hypervalent iodine; N-heterocycle; stability; thermogravimetry; Introduction Hypervalent iodine compounds, in particular aryl-λ3-iodanes, have found wide spread applications as oxidants and electrophilic group

Isolation of fungi using the diffusion chamber device FIND technology

• Benjamin Libor,
• Henrik Harms,
• Stefan Kehraus,
• Ekaterina Egereva,
• Max Crüsemann and
• Gabriele M. König

Beilstein J. Org. Chem. 2019, 15, 2191–2203, doi:10.3762/bjoc.15.216

• inserted into a tank containing 40 L of soil for experiment 1, 2 L of sea water and sediment for experiment 2, 20 L of sea water and sediment for experiment 3 and sea water for experiment 4. An aquarium powerhead pump provided water current for simulation, oxygenation and distribution purposes for

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

• (3b’ and 6b’) and anti-aromatic (4a’ and 5a’) ring currents. Reaction of 6,6-dimethylpentafulvene with singlet state oxygen to form an enol lactone via the multistep rearrangement proposed by Harada et al. (supporting information was not provided) [51]. Photosensitized oxygenation of 8

α-Photooxygenation of chiral aldehydes with singlet oxygen

• Dominika J. Walaszek,
• Magdalena Jawiczuk,
• Jakub Durka,
• Olga Drapała and
• Dorota Gryko

Beilstein J. Org. Chem. 2019, 15, 2076–2084, doi:10.3762/bjoc.15.205

• University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland 10.3762/bjoc.15.205 Abstract Organocatalytic α-oxygenation of chiral aldehydes with photochemically generated singlet oxygen allows synthesizing chiral 3-substituted 1,2-diols. Stereochemical results indicate that the reaction in the presence

• methodologies enabling their functionalization, particularly in a stereoselective manner. Among them, asymmetric α-oxygenation of aldehydes still represents a challenging task. Most efficient methods require simultaneous use of chiral amines or Brønsted acids, and harsh oxidants like nitrosobenzene [1][2][3

• small molecule size, there are few examples of its use not only in diastereoselective synthesis but also in enantioselective reactions [9][10]. Inspired by Cόrdova’s work [11][12][13], we explored the idea of merging enamine catalysis with photocatalytic oxygenation with singlet oxygen for α

A review of the total syntheses of triptolide

• Xiang Zhang,
• Zaozao Xiao and
• Hongtao Xu

Beilstein J. Org. Chem. 2019, 15, 1984–1995, doi:10.3762/bjoc.15.194

• -ring system; palladium-catalyzed carbonylation and in situ lactone formation, and rhodium(II)-catalyzed double bond migration to construct the D-ring; and palladium-catalyzed Csp2–H oxygenation to install the C-14 hydroxy group. In 2016, Qin and co-workers developed a catalytic asymmetric route toward

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

• oxygenation of substrates containing secondary benzylic C–H bonds, yielding the corresponding benzylic acetates in good to moderate yield. Tertiary benzylic C–H bonds were shown to be unreactive under similar conditions, despite the weaker C–H bond. A preliminary mechanistic analysis suggests that this NHPI

• . Results and Discussion We have recently reported a system of simple combinations of an iodine (III, V, or VII) oxide with a catalytic amount of chloride for the direct oxygenation of methane to its methyl ester [49][50]. Mechanistic studies of this system have indicated that these chloride-iodate

Synthesis of eunicellane-type bicycles embedding a 1,3-cyclohexadiene moiety

• Alex Frichert,
• Peter G. Jones and
• Thomas Lindel

Beilstein J. Org. Chem. 2018, 14, 2461–2467, doi:10.3762/bjoc.14.222

• ketoaldehyde precursor [11]. However, compound 8 proved to be very resistant towards any attempt of partial hydrogenation of the benzene moiety. Systems embedding a cyclohexadiene ring should be more versatile, e.g., by allowing regio- and stereoselective hydrogenation and oxygenation towards partial

One-pot synthesis of epoxides from benzyl alcohols and aldehydes

• Edwin Alfonzo,
• Jesse W. L. Mendoza and
• Aaron B. Beeler

Beilstein J. Org. Chem. 2018, 14, 2308–2312, doi:10.3762/bjoc.14.205

• -epoxide adduct 25 [35]. However, the one-pot reaction was highly successful with three electron-rich benzyl alcohols 26, 27, and 28 all bearing multiple oxygenation and with a large panel of electron-rich aldehydes (Figure 2). The reaction was highly successful even when both partners were poly-oxygenated

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

• resulting benzylic radicals. Recently, the precursors of N-oxyl radicals, such as N-hydroxyphthalimide (NHPI), N-hydroxysuccinimide (NHSI), N-hydroxybenzotriazole (HOBt) and hydroxamic acids, have been used in the reactions of radical oxygenation of styrenes [45]. Growth of interest is observed concerning

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

• -oxytosylation of ketones by using a new family of chiral hypervalent iodine catalyst 21 with up to 46% ee [67]. The investigation of the reaction mechanisms revealed that the steric crowding around the iodine center improves the enantioselectivity (Scheme 18). Asymmetric oxygenation and nitrogenation reactions

• ]. Latterly, Masson et al. reported a new chiral iodoarene prereagent 22 which they have used for the direct oxygenation of carbonyls 98. They were able to get α-sulfonyls and α-phosphoryl oxyketones 99 with moderate ees (Scheme 22) [72]. A new type of non C2-symmetric chiral hypervalent reagent was utilized

• for the asymmetric α-oxygenation of carbonyls. Nucleophilic attack of the oxygen nucleophile to the intermediate 100 or alternatively a reaction pathway through O-enolate intermediate 101 can explain the desired product formation. In 2014, Kita and Shibata reported a catalytic, enantioselective

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

• underwent di-π-methane photo-rearrangement to 210–212 exclusively (Scheme 35). Moreover, Dastan’s group prepared bicyclic endoperoxide 213 in 74% yield from 2,3-benzotropone (12) via tetraphenylporphyrine (TPP)-sensitized photo-oxygenation (Scheme 35) [149]. 3.2.4. Miscellaneous transformations: Machiguchi

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

• ; C–H activation; iodine; oxygenation; radicals; Introduction The oxidative activation of a C(sp3)–H bond in organic molecules to directly install various functional groups and new carbon–carbon networks is a topic of interest for researchers engaged in modern synthetic chemistry [1][2][3][4][5][6][7

• benzylic acetoxylation and benzoyloxylation of alkylbenzenes, where an in situ-generated sulfonamidyl radical is the essential radical mediator that effectively abstracts the benzylic hydrogen [49]. More recently, Maruoka et al. succeeded in the photolytic benzylic C–H bond oxygenation of alkylbenzenes

Hypervalent iodine(III)-mediated decarboxylative acetoxylation at tertiary and benzylic carbon centers

• Kensuke Kiyokawa,
• Daichi Okumatsu and
• Satoshi Minakata

Beilstein J. Org. Chem. 2018, 14, 1046–1050, doi:10.3762/bjoc.14.92

• esters as substrates [16]. Although the method was applicable to a broader range of substrates, the preparation of the activated ester is an intrinsic drawback to this procedure. While more convenient and practical methods for decarboxylative oxygenation, in which carboxylic acids are directly used as a

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation. Part 1: Use of CF₃SO₂Na

• Hélène Guyon,
• Hélène Chachignon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2764–2799, doi:10.3762/bjoc.13.272

• metal catalysts and/or a large excess of organic oxidants can be obstacles to production. In a quest for ideal conditions, Lei and co-workers exposed heteroatom-functionalised alkenes 14 to aerobic Cvinyl–heteroatom bond oxygenation under metal-free conditions, where oxygen from air worked in concert

Transition-metal-free synthesis of 3-sulfenylated chromones via KIO₃-catalyzed radical C(sp²)–H sulfenylation

• Yanhui Guo,
• Shanshan Zhong,
• Li Wei and
• Jie-Ping Wan

Beilstein J. Org. Chem. 2017, 13, 2017–2022, doi:10.3762/bjoc.13.199

• efforts in exploring enaminone C(sp2)–H bond sulfenylation [40][41] reactions have led us to establish the synthesis of 3-sulfenylated chromones via KIO3-catalyzed tandem reactions of o-hydroxylphenylenaminone and thiophenols via tandem C–H sulfenylation and intramolecular C–N bond oxygenation (B, Scheme

Chiral phase-transfer catalysis in the asymmetric α-heterofunctionalization of prochiral nucleophiles

• Johannes Schörgenhumer,
• Maximilian Tiffner and
• Mario Waser

Beilstein J. Org. Chem. 2017, 13, 1753–1769, doi:10.3762/bjoc.13.170

• ]. Besides those methods that make use of already α-functionalized carbonyl compounds, the direct stereoselective α-oxygenation or α-hydroxylation of simple prochiral nucleophiles with either oxygen as such, or an electrophilic oxygen species became by far the most important and most thoroughly investigated

• investigated. In 2008, Itoh’s group described the α-hydroxylation of oxindoles 17 under phase-transfer conditions by using air in combination with (EtO)3P as the oxygenation system (Scheme 8, upper reaction) [111]. Very recently, Zhao et al. then developed this elegant methodology further by identifying the

• and it is without doubt that it will inspire other groups to enter the field as well. A very remarkable strategy for the α-oxygenation of prochiral nucleophiles was recently reported by Ishihara and co-workers [125][126]. They succeeded in developing a highly enantioselective protocol for oxidative

Opportunities and challenges for the sustainable production of structurally complex diterpenoids in recombinant microbial systems

• Katarina Kemper,
• Max Hirte,
• Markus Reinbold,
• Monika Fuchs and
• Thomas Brück

Beilstein J. Org. Chem. 2017, 13, 845–854, doi:10.3762/bjoc.13.85

• biosyntheses involving multiple oxygenation steps challenging [93]. Even highly optimized systems for the production of just the first hydroxylated intermediate in taxol biosynthesis, 5-α-hydroxytaxadiene [91], show a product loss of over 40% in comparison to previously reported titers for the undecorated

• in-process-accumulation of the inhibitory metabolite indole [28]. A suitable method for most fermentations is an overlay with apolar alkanes such as dodecane [28][79][95] although subsequent product extraction from this phase may be challenging and oxygenation capacity is reduced. Engineering efflux

Transition-metal-catalyzed synthesis of phenols and aryl thiols

• Yajun Liu,
• Shasha Liu and
• Yan Xiao

Beilstein J. Org. Chem. 2017, 13, 589–611, doi:10.3762/bjoc.13.58

• hydroxylation of arenes: In 2012, Ackermann and co-workers used [Ru(O2CMes)2(p-cymene)] as catalyst to achieve the C–H bond oxygenation of N-substituted benzamides in TFA/TFAA. The reaction proceeded in the presence of PhI(OAc)2 as oxidant at 120 °C (Scheme 46) [75]. A broad scope of functional groups could be

A flow reactor setup for photochemistry of biphasic gas/liquid reactions

• Josef Schachtner,
• Patrick Bayer and
• Axel Jacobi von Wangelin

Beilstein J. Org. Chem. 2016, 12, 1798–1811, doi:10.3762/bjoc.12.170

• effectively under microflow conditions [41][42][50][51][74][75]. We applied the home-made photo-flow reactor (Figure 7) to the visible light mediated oxygenation of a cyclohexene derivative (i.e., Schenck ene reaction with singlet oxygen) [72][73] and evaluated the critical reaction and reactor parameters

Synthesis of β-arylated alkylamides via Pd-catalyzed one-pot installation of a directing group and C(sp³)–H arylation

• Yunyun Liu,
• Yi Zhang,
• Xiaoji Cao and
• Jie-Ping Wan

Beilstein J. Org. Chem. 2016, 12, 1122–1126, doi:10.3762/bjoc.12.108

• functionalization chemistry [35][36][37][38][39][40], we have executed efforts to the AQ-assisted β-C–H functionalization reactions of alkylamides via activation of the C(sp3)–H bond, a classical protocol toward β-arylamide synthesis. While the known examples, including C(sp3)–H alkylation, arylation or oxygenation

Biosynthesis of α-pyrones

• Till F. Schäberle

Beilstein J. Org. Chem. 2016, 12, 571–588, doi:10.3762/bjoc.12.56

• chestnut) showed antioxidant activity [28]. Testing urolithins A, B, C, D (23–26) in an assay using myelomonocytic HL-60 cells showed antioxidant activities for 23, 25 and 26. These three derivatives inhibited the reactive oxygen species (ROS)-dependent oxygenation of the non-fluorescent 2’,7

Base metal-catalyzed benzylic oxidation of (aryl)(heteroaryl)methanes with molecular oxygen

• Hans Sterckx,
• Johan De Houwer,
• Carl Mensch,
• Wouter Herrebout,
• Kourosch Abbaspour Tehrani and
• Bert U. W. Maes

Beilstein J. Org. Chem. 2016, 12, 144–153, doi:10.3762/bjoc.12.16

• ; catalyzed; molecular oxygen; oxygenation; Introduction Direct oxidation of C(sp3)–H bonds is a useful and fast method to convert fairly unreactive substrates to useful functional groups for organic synthesis like alcohols, ketones, aldehydes and carboxylic acids. Classical oxidation protocols rely on the

• with molecular oxygen can be used to perform benzylic oxidations [20]. The aerobic copper-catalyzed α-oxygenation of 2-arylthioacetamides was reported by Moghaddam [21]. In this transformation CuCl2 and K2CO3 in DMF were used to produce α-ketoarylthioacetamides. The coupling of 2-arylacetaldehydes with

• reactive alkyl-substituted pyridines. Gao showed that NH4I can also be used as an organocatalyst in combination with AcOH to facilitate the oxidation of benzylpyridines to benzoylpyridines [29]. Satoh and Miura showed that when replacing O2 for Na2S2O8 chemoselective methylenation occurred over oxygenation

Copper-catalyzed intermolecular oxyamination of olefins using carboxylic acids and O-benzoylhydroxylamines

• Brett N. Hemric and
• Qiu Wang

Beilstein J. Org. Chem. 2016, 12, 22–28, doi:10.3762/bjoc.12.4

• transformation, integrating an electrophilic amination with a nucleophilic oxygenation, builds upon our recent development in copper-catalyzed olefin difunctionalization, such as copper-catalyzed diamination [40] and amino lactonization [34]. This strategy overcomes common issues of chemo- and regioselectivity

• results suggest a contribution of the structural conformation to the diastereoselective outcome of the reaction. Yet, 1,1-disubstituted olefins were not effective, likely due to the increased steric hindrance in the oxygenation step (Table 2, entry 12). Currently, the mechanistic details of this copper