Come-back of phenanthridine and phenanthridinium derivatives in the 21st century

• Lidija-Marija Tumir,
• Marijana Radić Stojković and
• Ivo Piantanida

Beilstein J. Org. Chem. 2014, 10, 2930–2954, doi:10.3762/bjoc.10.312

• rather expensive; therefore efforts were made to replace them with cheaper analogues. One successful approach included iron(III) acetylacetonate in acetic acid as catalytic agent (Scheme 16) [37], whereby O-acetyl oximes obtained from 2′-arylacetophenones underwent N–O bond cleavage and intramolecular N

N–O Cleavage reactions of heterobicycloalkene-fused 2-isoxazolines

• Jaipal R. Nagireddy,
• Geoffrey K. Tranmer,
• Emily Carlson and
• William Tam

Beilstein J. Org. Chem. 2014, 10, 2200–2205, doi:10.3762/bjoc.10.227

• isoxazoline-cleavage methodology to the preparation of biologically active natural products, including novel antibacterial, antifungal and anticancer treatments [8][9][10][11]. Some common methods of reductive N–O bond cleavage in isoxazolines include hydrogenolysis using Raney nickel, reduction by LiAlH4

• we were able to prepare in a highly regio- and stereoselective manner [21]. Selective cleavage of the N–O bond or simultaneous cleavage of both N–O and bridge C–C bonds of these isoxazolines could provide novel routes to the aforementioned functionalities attached to heterobicyclic ring systems such

• mediation. These results are summarized in Table 2. Compared to the parent compound 10a which gave an appreciable 93% yield of the corresponding β-hydroxyketone (Table 2, entry 1), replacement of two of the arene hydrogens for bromine atoms in 10b resulted in a lower tendency toward N–O bond cleavage (Table

Isoxazolium N-ylides and 1-oxa-5-azahexa-1,3,5-trienes on the way from isoxazoles to 2H-1,3-oxazines

• Alexander F. Khlebnikov,
• Mikhail S. Novikov,
• Yelizaveta G. Gorbunova,
• Ekaterina E. Galenko,
• Kirill I. Mikhailov,
• Viktoriia V. Pakalnis and
• Margarita S. Avdontceva

Beilstein J. Org. Chem. 2014, 10, 1896–1905, doi:10.3762/bjoc.10.197

• very low activation barriers (0.2–1.5 kcal/mol) to give (3Z)-1-oxa-5-azahexa-1,3,5-trienes. This is expected, because the oxazole N–O bond is very weak and the reaction is pseudopericyclic [21][22]. The calculated low thermodynamic and kinetic stabilities of the isoxazolium ylides (Figure 1) give only

Synthesis of rigid p-terphenyl-linked carbohydrate mimetics

• Maja Kandziora and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2014, 10, 1749–1758, doi:10.3762/bjoc.10.182

• -couplings to form biphenyl aminopyran or p-terphenyl-linked dimers. Hydrogenolysis afforded new unnatural aminosugar mimetics. Zinc in the presence of acid or samarium diiodide were examined for the N–O bond cleavage in order to obtain the rigid p-terphenyl-linked C-glycosyl dimers. Keywords: carbohydrate

• simple monocyclic carbohydrate mimetics. To prepare phenyl-substituted aminopyrans the N–O bond of bicyclic compounds 15a and 15b was cleaved by hydrogenolysis. These reactions are challenging because the resulting aminopyrans are apparently poisoning the catalyst and hence large amounts of palladium on

• debromination. The debenzylation and the N–O bond cleavage occur as next steps. Under these improved conditions the isomeric bicyclic 1,2-oxazine 15b was converted into aminopyran 17b in a good yield of 77%. The formed aminopyrans 17a and 17b can be regarded as amino C-glycosides. Compound 17a is related to

Synthesis of new enantiopure poly(hydroxy)aminooxepanes as building blocks for multivalent carbohydrate mimetics

• Léa Bouché,
• Maja Kandziora and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2014, 10, 213–223, doi:10.3762/bjoc.10.17

• (CH2 next to the N–O bond). Finally, the TBS-groups were removed under standard conditions furnishing triols 14, 15 and 16 in high yields. The free primary hydroxy group of bicyclic ketone 11 was propargylated in 71% yield employing propargylic bromide under standard conditions (Scheme 7). After

• conditions using palladium on charcoal in order to remove the N-benzyl group and to cleave the N–O bond [47][48] in one step. This process is often challenging due to the difficult control of the various reaction parameters and also because of the high polarity of the newly formed compounds. According to the

An overview of the synthetic routes to the best selling drugs containing 6-membered heterocycles

• Marcus Baumann and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2013, 9, 2265–2319, doi:10.3762/bjoc.9.265

The chemistry of isoindole natural products

• Klaus Speck and
• Thomas Magauer

Beilstein J. Org. Chem. 2013, 9, 2048–2078, doi:10.3762/bjoc.9.243

• -step sequence yielded azetidine 107. After oxidation with hydrogen peroxide, the resulting N-oxide cleanly underwent a [1,2]-Meisenheimer rearrangement upon heating in tetrahydrofuran. The so-formed azocine 108 was converted to amine 109 by hydrogenolysis of the N–O bond. Amide formation with acid

An aniline dication-like transition state in the Bamberger rearrangement

• Shinichi Yamabe,
• Guixiang Zeng,
• Wei Guan and
• Shigeyoshi Sakaki

Beilstein J. Org. Chem. 2013, 9, 1073–1082, doi:10.3762/bjoc.9.119

• monoprotonated systems would arise from the poor proton-donating strength to the oxygen of the N–O bond in the model of Scheme 5. In order to enhance the donation, a dication system was constructed at the left of Scheme 6. However, the bond-interchange transition state could not be obtained in spite of many

• water cluster. The N-protonated substrate (5 in Scheme 4) is in the reaction route. By the protonation, the N–O bond becomes directed to the π space of the phenyl ring. The direction is fit for the subsequent bond interchange of TS2 in the diprotonated system. Without good nucleophiles such as Cl−, a

• constrained hydrogen-bond network shown in Scheme 7 may give the OH shift via bond interchanges. The ortho-position is too close to the N–O bond and is not fit for the constrained network. On the basis of the calculated results, Scheme 4 may be revised to Scheme 8. Geometric changes in the reaction of model

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

• N-tosyloxycarbamate 8 and azidoformate 3 under FeBr2/Bu4NBr in EtOH conditions (see Table 1, entry 1 versus Scheme 3) likely originate from the distinct chemical property of the N–iron species (i) generated from each substrate. The possible coordination of tosylate anion to the N–iron after the N–O

• bond cleavage with FeX2 may have affected the electronic and steric characters of intermediate (i), leading to retardation of the subsequent cyclization. Because of the low cyclization rate, the production of reduced carbamate 9 and enone 10 became pronounced. This is consistent with the observation

Enantioselective total synthesis of (R)-(−)-complanine

• Krystal A. D. Kamanos and
• Jonathan M. Withey

Beilstein J. Org. Chem. 2012, 8, 1695–1699, doi:10.3762/bjoc.8.192

• owing to N–O bond lability. Recent reports suggest that this O-nitrosoaldol reaction proceeds much more cleanly with 2-nitrosotoluene than with nitrosobenzene, probably owing to the suppression of N–O bond cleavage [10]. Thus, treatment of aldehyde 3 with 2-nitrosotoluene in the presence of L-proline as

• with sodium borohydride. Subsequent copper-mediated N–O bond cleavage gave chiral diol 8 in 97% ee (determined by HPLC analysis using a chiral stationary phase). Diol 8 had identical spectroscopic properties compared to those reported by Nakamura and Uemura and intercepted their synthesis of (R

Organocatalytic asymmetric allylic amination of Morita–Baylis–Hillman carbonates of isatins

• Hang Zhang,
• Shan-Jun Zhang,
• Qing-Qing Zhou,
• Lin Dong and
• Ying-Chun Chen

Beilstein J. Org. Chem. 2012, 8, 1241–1245, doi:10.3762/bjoc.8.139

• electron-withdrawing groups exhibited a slower reaction rate, but both good yields and ee values were still obtained (Table 2, entries 5–10). As outlined in Scheme 2, some synthetic transformations were conducted with the multifunctional allylic amination product 4d. The N–O bond cleavage of 4d could be

Carbohydrate-auxiliary assisted preparation of enantiopure 1,2-oxazine derivatives and aminopolyols

• Marcin Jasiński,
• Dieter Lentz and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2012, 8, 662–674, doi:10.3762/bjoc.8.74

• lithiated methoxyallene to give the double adduct G. After aqueous work-up, hydroxylamine derivative H underwent a ring-closure to 1,2-oxazetidine derivative I. It is known that this class of compounds can suffer a thermally induced [2 + 2] cycloreversion involving N–O bond cleavage [39][40], which, in our

Aryl nitrile oxide cycloaddition reactions in the presence of pinacol boronic acid ester

• Sarah L. Harding,
• Sebastian M. Marcuccio and
• G. Paul Savage

Beilstein J. Org. Chem. 2012, 8, 606–612, doi:10.3762/bjoc.8.67

• other 1,3-disubstituted compounds, through N–O bond cleavage [20]. Nitrile oxides are reactive intermediates that are usually generated in situ and react immediately with the dipolarophile. There have been many methods reported for the generation of nitrile oxides, but the most common one for alkyl

Gold-catalyzed regioselective oxidation of terminal allenes: formation of α-methanesulfonyloxy methyl ketones

• Yingdong Luo,
• Guozhu Zhang,
• Erik S. Hwang,
• Thomas A. Wilcoxon and
• Liming Zhang

Beilstein J. Org. Chem. 2011, 7, 596–600, doi:10.3762/bjoc.7.69

• undergo protonation to form intermediate F with MsO− as the counter anion. An SN2'-type substitution by the anion would afford the observed product. This substitution is facilitated by the fragmentation of the weak N–O bond and the annihilation of the charges. Conclusion We have successfully realized the

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

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

Recent progress on the total synthesis of acetogenins from Annonaceae

• Nianguang Li,
• Zhihao Shi,
• Yuping Tang,
• Jianwei Chen and
• Xiang Li

Beilstein J. Org. Chem. 2008, 4, No. 48, doi:10.3762/bjoc.4.48

• followed by N-O bond cleavage and elimination of the aryl amine to reintroduce the butenolide unsaturation afforded 143. Then coupling reaction between 136 and 140 provided 144, which was readily transformed into 145. Sonogashira cross-coupling of 145 with the vinyl iodide 143 followed by selective

Synthesis of densely functionalized enantiopure indolizidines by ring- closing metathesis (RCM) of hydroxylamines from carbohydrate- derived nitrones

• Marco Bonanni,
• Marco Marradi,
• Francesca Cardona,
• Stefano Cicchi and
• Andrea Goti

Beilstein J. Org. Chem. 2007, 3, No. 44, doi:10.1186/1860-5397-3-44

• this reason the crude reaction mixtures were directly employed in the following steps. Identity of compounds 12 and 13 was firmly established after their transformation into the corresponding amines and further elaboration. After deacetylation with KHCO3, in situ reduction of the N-O bond with zinc