Metal and metal-free photocatalysts: mechanistic approach and application as photoinitiators of photopolymerization

• Jacques Lalevée,
• Sofia Telitel,
• Pu Xiao,
• Marc Lepeltier,
• Frédéric Dumur,
• Fabrice Morlet-Savary,
• Didier Gigmes and
• Jean-Pierre Fouassier

Beilstein J. Org. Chem. 2014, 10, 863–876, doi:10.3762/bjoc.10.83

• through a subsequent Ph•/R3SiH hydrogen abstraction and R3Si•/PIC•+ interaction, respectively (the eA serves both as an electron donor and a radical mediator source) [45][46][47][48][49][50][51][52]. The Ph2I+/R3Si• interaction increases the yields in both phenyl radicals and silylium species [45][46][47

Elucidation of the regio- and chemoselectivity of enzymatic allylic oxidations with Pleurotus sapidus – conversion of selected spirocyclic terpenoids and computational analysis

• Verena Weidmann,
• Mathias Schaffrath,
• Holger Zorn,
• Julia Rehbein and
• Wolfgang Maison

Beilstein J. Org. Chem. 2013, 9, 2233–2241, doi:10.3762/bjoc.9.262

• hydrogen abstraction in position 2, spiroether 7 was selectively converted to the spirolactone 14. The alternative oxidation product 15 was not found by GC–MS. The regioisomeric spiroether 8 offers only one plausible path for allylic oxidation in position 3. However, this spiroether was not converted at

• for oxidation of spiroethers 11 and 12 which contain two separated double bonds. The allyl ether 11 allows three plausible oxidation products 17–19. However, due to our experiences with oxidations of 7, 8 and theaspirane (1), position 2 should be activated most strongly for hydrogen abstraction and

Damage of polyesters by the atmospheric free radical oxidant NO₃^•: a product study involving model systems

• Catrin Goeschen and
• Uta Wille

Beilstein J. Org. Chem. 2013, 9, 1907–1916, doi:10.3762/bjoc.9.225

• materials, the chemical mechanism of polymer degradation is by far not fully understood. It has generally been assumed that polymer degradation involves a radical-mediated autoxidation mechanism, which propagates through hydrogen abstraction by an intermediate peroxyl radical ROO•. Although this

• transformation processes at night. NO3•, which is formed through reaction of the atmospheric pollutants nitrogen dioxide, NO2•, with ozone, O3 (Scheme 1a) [7][8], reacts with organic compounds through various pathways, such as hydrogen abstraction (HAT) and addition to π systems. Most importantly, NO3• is one of

• , particularly the neopentyl moiety, which is a potential pathway that should most likely occur at the methylene groups α to the ester oxygen atom [18][19][20], is apparently not a feasible pathway. This finding is of potential relevance for the autoxidation mechanism, which proposes hydrogen abstraction by ROO

Aerobic radical multifunctionalization of alkenes using tert-butyl nitrite and water

• Daisuke Hirose and
• Tsuyoshi Taniguchi

Beilstein J. Org. Chem. 2013, 9, 1713–1717, doi:10.3762/bjoc.9.196

• nitrate ester 24 was detected in the reaction of 14. This implies that the 1,5-hydrogen shift on the methine site is not so fast (entry 10). Typically, in the radical hydrogen abstraction, a methine C–H bond is more reactive than methyl and methylene sites, whereas it might be difficult for substrates

A reductive coupling strategy towards ripostatin A

• Kristin D. Schleicher and
• Timothy F. Jamison

Beilstein J. Org. Chem. 2013, 9, 1533–1550, doi:10.3762/bjoc.9.175

• sensitive to strong base as well as hydrogen abstraction [10][11]. While classical methods for the preparation of 1,4-dienes include partial reduction of alkynes and carbonyl olefination, a variety of transition-metal-mediated processes have been developed for the synthesis of skipped dienes of varied

Electron self-exchange activation parameters of diethyl sulfide and tetrahydrothiophene

• Martin Goez and
• Martin Vogtherr

Beilstein J. Org. Chem. 2013, 9, 1448–1454, doi:10.3762/bjoc.9.164

• reaction into a hydrogen abstraction. In a previous report on two aliphatic amines [20], we have used time-resolved CIDNP experiments to distinguish between the ensuing electron and hydrogen self-exchanges of D•+ and . In the present work, we investigate two structurally similar aliphatic sulfides

A construction of 4,4-spirocyclic γ-lactams by tandem radical cyclization with carbon monoxide

• Mitsuhiro Ueda,
• Yoshitaka Uenoyama,
• Nozomi Terasoma,
• Shoko Doi,
• Shoji Kobayashi,
• Ilhyong Ryu and
• John A. Murphy

Beilstein J. Org. Chem. 2013, 9, 1340–1345, doi:10.3762/bjoc.9.151

• (Scheme 6). Then, the THF radical is formed via the α-hydrogen abstraction by the azidyl radical [31][32][33][34], which is attached to G to give α-carbonyl radical H. Finally, H abstracts hydrogen from TTMSS, affording the THF-incorporating product 3 and the (TMS)3Si radical, which participates in the

Preparation of optically active bicyclodihydrosiloles by a radical cascade reaction

• Koichiro Miyazaki,
• Yu Yamane,
• Ryuichiro Yo,
• Hidemitsu Uno and
• Akio Kamimura

Beilstein J. Org. Chem. 2013, 9, 1326–1332, doi:10.3762/bjoc.9.149

• process reaches 2.4 × 105 s−1 at 80 °C [25]. Although most of the Me3Si radicals undergo hydrogen abstraction from (Me3Si)3SiH to yield a new (Me3Si)3Si radical and Me3SiH, a small fraction of the Me3Si radicals compete to attack 1; a similar cascade reaction progresses consequently, and compound 3 is

• hydrogen abstraction from (Me3Si)3SiH, even under high concentration conditions. Second, the addition rate of (Me3Si)3Si radicals to alkenes should be relatively slow; the rate competes with the addition rate of Me3Si radicals to alkenes. This reason is supported by the results that indicated the yield of

Metal-free aerobic oxidations mediated by N-hydroxyphthalimide. A concise review

• Lucio Melone and
• Carlo Punta

Beilstein J. Org. Chem. 2013, 9, 1296–1310, doi:10.3762/bjoc.9.146

• oxidation of organic substrates [7][8][9][10][11]. NHPI acts as a precursor of the phthalimide N-oxyl (PINO) radical, which is the effective catalyst promoting hydrogen-abstraction processes (Scheme 1). The reactivity of NHPI and PINO is related to the bond dissociation energy (BDE) of the O–H group, which

• was estimated at 88.1 kcal/mol [12]. This value is similar to the BDE of O–H in hydroperoxides, suggesting that the faster reactivity of PINO compared to peroxyl radicals should be attributed to an enhanced polar effect involved in the hydrogen abstraction by this nitroxyl radical [13]. Furthermore

• BDE value (79.2 kcal/mol [12]), NMBHA turned out to be a better candidate than NHPI to act both as autoxidation catalyst, promoting the hydrogen abstraction from the bisallylic C–H position of the fatty esters by means of the corresponding amidoxyl radical, and as a good hydrogen donor (kH = 1.2 × 105

Formal synthesis of (−)-agelastatin A: an iron(II)-mediated cyclization strategy

• Daisuke Shigeoka,
• Takuma Kamon and
• Takehiko Yoshimitsu

Beilstein J. Org. Chem. 2013, 9, 860–865, doi:10.3762/bjoc.9.99

• reactive FeX2 through capture with the polar amide functionality of 8. It is speculated that product 9 may be produced by trapping N–iron complex (i) with another FeX2 (i→vii→9), whereas enone 10 is likely to be generated via intramolecular allylic hydrogen abstraction followed by halogen transfer to

• that may account for the production of carbamate 9 through the regeneration of FeX2 species is the intermolecular hydrogen abstraction from substrate 8 by N–iron species (i) (Scheme 5). The intermediacy of the intermolecular hydrogen abstraction of N–iron species (i) is supported by the fact that the

• significant [42]. Various yields of 9 obtained by loading consistent amounts (1.2–1.5 equiv) of Bu4NX salts also indicated the poor contribution of the pathway. Chan and co-workers demonstrated that an iron–imido complex generated from FeCl2/PhI=NTs underwent radical hydrogen abstraction from a formyl group

Radical zinc-atom-transfer-based carbozincation of haloalkynes with dialkylzincs

• Fabrice Chemla,
• Florian Dulong,
• Franck Ferreira and
• Alejandro Pérez-Luna

Beilstein J. Org. Chem. 2013, 9, 236–245, doi:10.3762/bjoc.9.28

• , Me2Zn showed a similar reactivity to its higher homologues Et2Zn and n-Bu2Zn, with the additional advantage that no direct formation of vinyl bromide (E)-4ac by hydrogen abstraction was observed. In the presence of 5 equiv iPrI, a mixture of two (diastereomerically pure) compounds 4ad and 4ac in 87:13

Photochemical and thermal intramolecular 1,3-dipolar cycloaddition reactions of new o-stilbene-methylene-3-sydnones and their synthesis

• Kristina Butković,
• Željko Marinić,
• Krešimir Molčanov,
• Biserka Kojić-Prodić and
• Marija Šindler-Kulyk

Beilstein J. Org. Chem. 2011, 7, 1663–1670, doi:10.3762/bjoc.7.196

• , lose CO2 under the reaction conditions to afford intermediates 14A and 14 B, respectively. Owing to the favourable conformation in the case of biradical 15A, the 1,3-H abstraction and formation of the C–N double bond in product 15 is possible. In the biradical 14A the intramolecular hydrogen

• abstraction is not favourable, but 1,2-alkyl shift takes place followed by formation of the N–N double bond in product 14. Monitoring the reaction by thin layer chromatography revealed that the [3 + 2] cycloaddition is much faster in the case of the trans isomer (3a). After the 4 h reflux of the toluene

The arene–alkene photocycloaddition

• Ursula Streit and
• Christian G. Bochet

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

• completely new reaction Sakamoto has proposed a mechanism involving a ζ-hydrogen abstraction to form a biradical intermediate (Scheme 35, E). The resulting biradical cyclizes to form the spiro compound F upon recombination of the biradical. Re-aromatization affords the carboxylate G, which further attacks

• reactions are known to take place via a δ-hydrogen abstraction by the ketone triplet, followed by cyclization of the 1,5-biradical intermediate [103]. Griesbeck et al. investigated the mechanism for this photocycloaddition, as he suggested that the mechanism proposed by Jones is unlikely, because the

Photoinduced electron-transfer chemistry of the bielectrophoric N-phthaloyl derivatives of the amino acids tyrosine, histidine and tryptophan

• Axel G. Griesbeck,
• Jörg Neudörfl and
• Alan de Kiff

Beilstein J. Org. Chem. 2011, 7, 518–524, doi:10.3762/bjoc.7.60

• +, electronically excited phthalimides are potent electron acceptors [2]. The rich photochemistry of this chromophore has recently been reviewed [3][4]. Intramolecular hydrogen abstraction is an archetype process for electronically excited carbonyl groups (Norrish type II reaction). The 1,4-biradicals formed by γ

Anion–π interactions influence pK_a values

• Christopher J. Cadman and
• Anna K. Croft

Beilstein J. Org. Chem. 2011, 7, 320–328, doi:10.3762/bjoc.7.42

• -naphthol derivatives 1–5. These derivatives exhibit changes in their pKa' values consistent with the changing electronic nature of R substituent, suggesting an anion–π effect in modulating the hydrogen abstraction process. Density functional calculations indicate that the change in reactivity is likely to

Photocycloadditions and photorearrangements

• Axel G. Griesbeck

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

• spin-specific reactivities and selectivities. Additionally, the nature of the excited state, as characterized by the state configuration, is crucial for the reactivity of the molecule, for example, nπ* states favour hydrogen abstraction and addition modes whereas ππ* states favour addition and electron

Synthesis of bis(3-{[2-(allyloxy)ethoxy]methyl}-2,4,6-trimethylbenzoyl)(phenyl)phosphine oxide – a tailor-made photoinitiator for dental adhesives

• Norbert Moszner,
• Iris Lamparth,
• Jörg Angermann,
• Urs Karl Fischer,
• Frank Zeuner,
• Thorsten Bock,
• Robert Liska and
• Volker Rheinberger

Beilstein J. Org. Chem. 2010, 6, No. 26, doi:10.3762/bjoc.6.26

• ]. The CQ-A PIs belong to bimolecular hydrogen abstraction PI systems: CQ shows a broad absorption spectrum between 400 and 500 nm (λmax = 468 nm). The VL-excited CQ forms an excited state complex with the amine co-initiator, which generates a ketyl and an α-aminoalkyl radical by electron and subsequent

Synthesis of chiral cyclohexanes and carbasugars by 6-exo-dig radical cyclisation reactions

• Rajeev K. Shrivastava,
• Elise Maudru,
• Gurdial Singh,
• Richard H. Wightman and
• Keith M. Morgan

Beilstein J. Org. Chem. 2008, 4, No. 43, doi:10.3762/bjoc.4.43

• -hydrogen abstraction leading to a resonance stabilised allylic radical is favourable, a reaction which may in fact be synthetically useful. We have previously reported the synthesis of cyclohexanes and carbasugars that uses a 6-exo-dig cyclisation [20] and herein we report on our current endeavours in this

Part 2. Mechanistic aspects of the reduction of S-alkyl- thionocarbonates in the presence of triethylborane and air

• Florent Allais,
• Jean Boivin and
• Van Tai Nguyen

Beilstein J. Org. Chem. 2007, 3, No. 46, doi:10.1186/1860-5397-3-46

• Materials, 3B, Quang Trung, Hanoi, Vietnam 10.1186/1860-5397-3-46 Abstract Experiments conducted with deuterated compounds demonstrated that during the reduction of S-alkylxanthates with triethylborane, the hydrogen atom transferred has several competing origins. Hydrogen abstraction from water (or an

• found. A more seemly hypothesis is a hydrogen abstraction from the α-position of the boron atom. This reaction is well documented and energetically acceptable (BDE (C-H) = 80 ± 3 kcal/mol). For example, the methyl radical abstracts α-boronyl hydrogen of Et3B 124 times faster than hydrogen in the methyl

• a complexation would lower the BDE of the O-H bond by 30 kcal/mol when compared to free H2O, thus rendering hydrogen abstraction from water a plausible process. The second route implies hydrogen abstraction from •O-O-H radical (O-H BDE 47.6 kcal/mol). The latter could possibly be formed by