A simple and efficient method for the preparation of 5-hydroxy-3-acyltetramic acids

• Johanna Trenner and
• Evgeny V. Prusov

Beilstein J. Org. Chem. 2015, 11, 323–327, doi:10.3762/bjoc.11.37

• turned to the alternative oxidation of enolates with molecular oxygen in the presence of triethyl phosphite as originally described by Hartwig [12][13][14][15]. Application of these conditions resulted in a clean conversion to the 5-hydroxy-3-acyltetramic acid but again, the isolated yield of the product

• amounts of Pd trifluoroacetate/dppp [18] gave no conversion. In summary, we have developed a simple and efficient method for the synthesis of 5-hydroxy-3-acyltetramic acids by oxidation of the corresponding bisenolates with molecular oxygen. We have also investigated the cleavage of various protecting

• Johanna Trenner Evgeny V. Prusov Department of Medicinal Chemistry, Helmholtz Centre for Infection Research, Inhoffenstr. 7, 38124 Braunschweig, Germany 10.3762/bjoc.11.37 Abstract Oxidation of the bisenolates of 3-acyltetramic acid to the corresponding 5-hydroxylated compounds using molecular

Pd/C-catalyzed aerobic oxidative esterification of alcohols and aldehydes: a highly efficient microwave-assisted green protocol

• Marina Caporaso,
• Giancarlo Cravotto,
• Spyros Georgakopoulos,
• George Heropoulos,
• Katia Martina and
• Silvia Tagliapietra

Beilstein J. Org. Chem. 2014, 10, 1454–1461, doi:10.3762/bjoc.10.149

• friendly microwave-assisted oxidative esterification of alcohols and aldehydes in the presence of molecular oxygen and a heterogeneous catalysis (Pd/C, 5 mol %). This efficient and ligandless conversion procedure does not require the addition of an organic hydrogen acceptor. The reaction rate is strongly

• Selective oxidations of alcohols are some of the most important transformations in organic synthesis. Therefore, reactions that employ reusable heterogeneous catalysts and molecular oxygen are highly desirable from atom economy and environmental impact point of view [1][2][3]. A number of methods have been

• presence of molecular oxygen or air have been described [23][25][40][41][42][43], however, the main limit of this process is its lack of selectivity, as has already been reported. Several Pd-catalyzed procedures have been optimized and Ag [31][32] or Bi salts [40], hydrosilanes [33] or specially designed

Cyclization–endoperoxidation cascade reactions of dienes mediated by a pyrylium photoredox catalyst

• Nathan J. Gesmundo and
• David A. Nicewicz

Beilstein J. Org. Chem. 2014, 10, 1272–1281, doi:10.3762/bjoc.10.128

• % yield after 5 hours (Table 1, entry 1). The observed endoperoxide was attributed to a 5-exo cyclization mode of the diene cation radical followed by capture of molecular oxygen. The use of acetonitrile as solvent gave none of the desired adducts (Table 1, entry 2). Further improvement of the chemical

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

• ) [235]. This reaction gives β-hydroxyketones as by-products that are formed as a result of the decomposition of dioxolanes 14. Cyclopropanols 15a–g are readily oxidized by molecular oxygen in the presence of Mn(II) abietate or acetylacetonate (Scheme 6) [236]. Presumably, the reaction proceeds via the

• the Co(II)/Et3SiH/O2 system (Isayama–Mukaiyama reaction) Peroxysilylation of alkenes with molecular oxygen in the presence of triethylsilane catalyzed by cobalt(II) diketonates was described for the first time by S. Isayama and T. Mukaiyama in 1989 [246][247]. Currently, this approach is one of the

Synthesis of enantiomerically pure N-(2,3-dihydroxypropyl)arylamides via oxidative esterification

• Akula Raghunadh,
• Satish S More,
• T. Krishna Chaitanya,
• Yadla Sateesh Kumar,
• Suresh Babu Meruva,
• L. Vaikunta Rao and
• U. K. Syam Kumar

Beilstein J. Org. Chem. 2013, 9, 2129–2136, doi:10.3762/bjoc.9.250

• by the Breslow intermediate 11 to provide the corresponding Aldol products [36]. Studer et al. reported the preparation of acids by an oxidation of Breslow intermediates with molecular oxygen [37][38][39]. The highly activated Breslow intermediate 11 formed by the addition of the NHC to the aldehydes

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

• 10.3762/bjoc.9.196 Abstract Water induces a change in the product of radical multifunctionalization reactions of aliphatic alkenes involving an sp3 C–H functionalization by an 1,5-hydrogen shift using tert-butyl nitrite and molecular oxygen. The reaction without water, reported previously, gives nitrated

• molecular oxygen, an alkoxy radical 26 is formed from the peroxynitrite intermediate (ROONO) generated by the reaction of the peroxy radical (ROO•) intermediate with t-BuONO. The alkoxy radical causes an 1,5-hydrogen shift to give the corresponding alkyl radical 27 followed by formation of another alkoxy

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

• -catalysts, they are activated to the corresponding N-oxyl radical species and become able to promote radical chains, involving molecular oxygen, directly or indirectly. Most of the examples reported in the literature describe the use of these N-hydroxy derivatives in the presence of transition-metal

• the O2-mediated selective oxidation of organic compounds and looking for environmentally safe alternatives to metal catalysis. Keywords: autoxidation; free-radicals; metal-free; molecular oxygen; N-hydroxyphthalimide; Introduction The development of efficient and cheap catalytic systems for the

• selective oxidation of organic substrates under mild and environmentally benign conditions represents one of the major challenges in organic synthesis [1]. In this context, the replacement of traditional oxidants, often used in stoichiometric amounts, with molecular oxygen is mandatory in order to improve

Copper-catalyzed aerobic aliphatic C–H oxygenation with hydroperoxides

• Pei Chui Too,
• Ya Lin Tnay and
• Shunsuke Chiba

Beilstein J. Org. Chem. 2013, 9, 1217–1225, doi:10.3762/bjoc.9.138

• aerobic oxygenation of aliphatic C–H bonds with hydroperoxides, which proceeds by 1,5-H radical shift of putative oxygen-centered radicals (O-radicals) derived from hydroperoxides followed by trapping of the resulting carbon-centered radicals with molecular oxygen. Keywords: copper; 1,4-diols; free

• radical; 1,5-H radical shift; hydroperoxides; molecular oxygen; Introduction Aliphatic sp3 C–H bonds are ubiquitous components in organic molecules but rather inert towards most of the chemical reactions. It thus remains as one of the most challenging topics in organic synthesis to develop catalytic

• radicals (C-radicals) could be trapped by molecular oxygen to form new C–O bonds. For instance, the Cu-catalyzed aerobic reaction of N-alkylamidines afforded aminidyl radicals (N-radicals) by single-electron oxidation and deprotonation of the amidine moiety, which was followed by 1,5-H-radical shift to

Substituent effect on the energy barrier for σ-bond formation from π-single-bonded species, singlet 2,2-dialkoxycyclopentane-1,3-diyls

• Jianhuai Ye,
• Yoshihisa Fujiwara and
• Manabu Abe

Beilstein J. Org. Chem. 2013, 9, 925–933, doi:10.3762/bjoc.9.106

• molecular oxygen (decay trace at 580 nm, Figure 2c); and (d) the activation parameters (Table 1) are similar to those for the decay process of DRa, in particular, the high (ca. 1012 s−1) pre-exponential Arrhenius factors (logA) are indicative of a spin-allowed reaction to the ring-closed products CPc–g [34

Palladium-catalyzed dual C–H or N–H functionalization of unfunctionalized indole derivatives with alkenes and arenes

• Gianluigi Broggini,
• Egle M. Beccalli,
• Andrea Fasana and
• Silvia Gazzola

Beilstein J. Org. Chem. 2012, 8, 1730–1746, doi:10.3762/bjoc.8.198

• -alkenylindoles in an atmosphere of molecular oxygen provided dihydroindoloazocine compounds that are key intermediates in the total synthesis of the austamide derivatives and the okaramine family of polycyclic bisindole alkaloids [73][74]. Enantioselective synthesis of vinyl-substituted tetrahydro-β-carbolines

Multistep organic synthesis of modular photosystems

• Naomi Sakai and
• Stefan Matile

Beilstein J. Org. Chem. 2012, 8, 897–904, doi:10.3762/bjoc.8.102

• 40. Addition of a second thioacetate gave dithioester 41, which was hydrolyzed with a base. Oxidation of dithiol 42 with molecular oxygen gave asparagusic acid (43), which is the natural product that contributes to the characteristic odor of asparagus. Activation with NHS gave the ester 28, ready for

Synthesis and photooxidation of styrene copolymer bearing camphorquinone pendant groups

• Branislav Husár,
• Norbert Moszner and
• Ivan Lukáč

Beilstein J. Org. Chem. 2012, 8, 337–343, doi:10.3762/bjoc.8.37

• CQ photooxidation in PS are summarized in Scheme 3 [21]. The addition of molecular oxygen to the excited n→π* triplet state of ketones and 1,2-diketones to form 1,4-biradicals is a generally accepted mechanism, which has been theoretically treated and reviewed [37]. The oxygen atom released during

• intermediate is most probably not formed. Similar to BZ, the n→π* triplet state of the CQ structure may also add molecular oxygen to form a 1,4-biradical. In the case of the BZ structures, formation of the 1,4-biradical is followed by BP formation. In comparison, CQ structures react with oxygen forming 1,4

CuCl-catalyzed aerobic oxidation of 2,3-allenols to 1,2-allenic ketones with 1:1 combination of phenanthroline and bipyridine as ligands

• Shuxu Gao,
• Yu Liu and
• Shengming Ma

Beilstein J. Org. Chem. 2011, 7, 396–403, doi:10.3762/bjoc.7.51

• , Chinese Academy of Sciences, 345 Lingling Lu, Shanghai 200032, P. R. China. Fax: (+86)-21-6260-9305 10.3762/bjoc.7.51 Abstract A protocol has been developed to prepare 1,2-allenyl ketones using molecular oxygen in air or pure oxygen as the oxidant from 2,3-allenylic alcohols with moderate to good yields

• employed for this type of transformation. However, the cost and the byproducts derived from these reagents cause economic and environmental problems [5]. In the past decades, much attention has been paid to catalytic oxidation of alcohols using molecular oxygen as the oxidant with Pd [6][7][8][9][10], Cu

• 73% conversion of 1l within 10 hours. Conclusion In conclusion, we have developed a method for the aerobic oxidation of 2,3-allenols, which uses molecular oxygen in air or pure oxygen as the oxidant. In this reaction, CuCl with a 1:1 ratio of 1,10-phenanthroline and bipyridine was used as the

Synthesis and crossover reaction of TEMPO containing block copolymer via ROMP

• Olubummo Adekunle,
• Susanne Tanner and
• Wolfgang H. Binder

Beilstein J. Org. Chem. 2010, 6, No. 59, doi:10.3762/bjoc.6.59

•  1) and related complexes as initiators, polymerization reactions can now not only be performed in protic media but also without rigorous exclusion of molecular oxygen. However, these advantages are hampered by the considerable lower activity of catalysts such as G1 when compared with Schrock’s

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

Beilstein J. Org. Chem. 2009, 5, No. 33, doi:10.3762/bjoc.5.33

• successful approach involved deprotection of the benzyl ether to generate the corresponding phenol 219 followed by reduction of the ester with lithium aluminium hydride and direct oxidation of the phenol to the quinone 221 with molecular oxygen and a catalytic amount of salcomine in an overall 30% yield over

Large- scale ruthenium- and enzyme- catalyzed dynamic kinetic resolution of (rac)-1-phenylethanol

• Krisztián Bogár,
• Belén Martín-Matute and
• Jan-E. Bäckvall

Beilstein J. Org. Chem. 2007, 3, No. 50, doi:10.1186/1860-5397-3-50

• reaction is performed on a 1 mmol scale, 4 mol% of ruthenium complex 1 is used for an efficient reaction.[32][34] We believe that the need of this high catalyst loading is due to a fast decomposition of the ruthenium active intermediates in the presence of small amounts of molecular oxygen. To test this

• hours under an oxygen atmosphere. We envisioned that running the reaction on a larger scale would allow a decrease in the catalyst loading, since decomposition of the catalyst due to the presence of traces of molecular oxygen may be avoided. The reaction in Scheme 1 (under argon) was therefore run on a

Photosonochemical catalytic ring opening of α-epoxyketones

• Hamid R. Memarian and
• Ali Saffar-Teluri

Beilstein J. Org. Chem. 2007, 3, No. 2, doi:10.1186/1860-5397-3-2

• electron transfer reactions by dicyanoanthracene (DCA), [32][33] tetracyanoethylene (TCNE) [34][35] and 2,4,6-triphenylpyrilium tetrafluoroborate. [36][37][38][39][40] In the case of C-C bond cleavage, the generated intermediates from epoxide radical cations have been trapped by molecular oxygen to form