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

• . Unnatural divalent rigid p-terphenyl-linked C-aryl glycosides with 2.0 nm dimension are available using Suzuki cross-couplings. The key compound, a p-bromophenyl-substituted 1,2-oxazine, was prepared by a stereoselective [3 + 3]-cyclization of a D-isoascorbic acid-derived (Z)-nitrone and lithiated TMSE

• -allene. The Lewis acid-induced rearrangement of this heterocycle provided the corresponding bicyclic 1,2-oxazine derivative that may be regarded as internally protected amino sugar analogue. After subsequent reduction of the carbonyl group, the resulting bicyclic compound was used for Suzuki cross

• bicyclic 1,2-oxazine derivative 3 was used as key building block for the Suzuki cross-coupling reaction to synthesize p-terphenyl-linked derivatives 1. The key intermediate 3 was prepared by a Lewis acid-induced rearrangement of 3,6-dihydro-2H-oxazine 4, that origins from a stereoselective [3 + 3

Multicomponent reactions in nucleoside chemistry

• Mariola Koszytkowska-Stawińska and
• Włodzimierz Buchowicz

Beilstein J. Org. Chem. 2014, 10, 1706–1732, doi:10.3762/bjoc.10.179

• Rai in the synthesis of nucleoside analogs 111 and 112 bearing novel nucleobase derived from benzo[e][1,3]oxazine (Scheme 46) [123]. The developed reactions were much more effective than those examined on other inorganic supports (i.e., silica gel, neutral or basic alumina). The conversion of the

• sugar urea to the corresponding isocyanate intermediate, accompanied by the loss of ammonia, was postulated to be the key step of the reaction cascade. Another approach to nucleoside analogs bearing a nucleobase derived from benzo[e][1,3]oxazine was developed by Rai and Singh (Scheme 47) [124]. The

Magnesium bis(monoperoxyphthalate) hexahydrate as mild and efficient oxidant for the synthesis of selenones

• Andrea Temperini,
• Massimo Curini,
• Ornelio Rosati and
• Lucio Minuti

Beilstein J. Org. Chem. 2014, 10, 1267–1271, doi:10.3762/bjoc.10.127

• , the corresponding oxirane 3e in 77% yield, resembling the previously reported one by oxidation with MCPBA (73% [9]). The MMPP oxidation of β-benzoylamino phenyl selenide 1f in methanol afforded exclusively the 1,3-oxazine 3f in excellent yield (84%). This result is in accordance with data reported by

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

• enantiopure nitrones and lithiated TMSE-allene we prepared three 1,2-oxazine derivatives which underwent a highly stereoselective Lewis acid-induced rearrangement to give bicyclic products in good yield. Subsequent reductive transformations delivered a library of new poly(hydroxy)aminooxepane derivatives. The

• crucial final palladium-catalyzed hydrogenolysis of the 1,2-oxazine moiety was optimized resulting in a reasonably efficient approach to a series of new seven-membered carbohydrate mimetics. Keywords: aminooxepanes; carbohydrate mimetics; hydrogenolyses; Lewis acid-induced; lithiated allenes; nitrones

• with excellent diastereoselectivities (Scheme 3). The nitrone 3 was used as a 96:4 mixture (with respect to the stereogenic center of the 1,3-dioxolane ring) and it could therefore provide four diasteromers of 1,2-oxazine syn-10 (two major syn- and two minor anti-diasteromeres), but only a single syn

Gold(I)-catalyzed enantioselective cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2013, 9, 2250–2264, doi:10.3762/bjoc.9.264

• -(1-alkynyl)-2-alken-1-ones 26 and nitrones. The reactions provide fused heterobicyclic oxazine derivatives of type 27 with good yields and excellent regio- and diastereoselectivities. The racemic series, promoted by Ph3PAuCl/AgOTf as a catalyst [84], was translated into an enantioselective version by

The chemistry of amine radical cations produced by visible light photoredox catalysis

• Jie Hu,
• Jiang Wang,
• Theresa H. Nguyen and
• Nan Zheng

Beilstein J. Org. Chem. 2013, 9, 1977–2001, doi:10.3762/bjoc.9.234

• and coworkers then applied the same strategy to prepare two other types of heterocycles, isoquino[2,1-a][3,1]oxazine and isoquino[2,1-a]pyrimidine (75, Scheme 19) [87]. The use of [Ir(ppy)2(dtbbpy)](PF6) with air as the external oxidant was found to be optimal for catalyzing the reaction. Later, the

• Marvin group reported an identical synthesis of isoquino[2,1-a][3,1]oxazine using Ru(bpy)3Cl2 instead [88]. The tethered nucleophiles, primary alcohols or sulfonamides, are part of the N-aryl group of tetrahydroisoquinolines 73. Similar to the synthesis of tetrahydroimidazoles 72, MeOH was the optimal

Amyloid-β probes: Review of structure–activity and brain-kinetics relationships

• Todd J. Eckroat,
• Abdelrahman S. Mayhoub and
• Sylvie Garneau-Tsodikova

Beilstein J. Org. Chem. 2013, 9, 1012–1044, doi:10.3762/bjoc.9.116

Synthesis of meso-substituted dihydro-1,3-oxazinoporphyrins

• Satyasheel Sharma and
• Mahendra Nath

Beilstein J. Org. Chem. 2013, 9, 496–502, doi:10.3762/bjoc.9.53

• -oxazine ring system were successfully synthesized from 5-(4-aminophenyl)-10,15,20-triphenylporphyrin in good yields. The structures of the target products were established on the basis of spectral data and elemental analyses. Keywords: dihydro-1,3-oxazinoporphyrins; iminoporphyrins; La(OTf)3; Mannich

• cancers [30]. Thorough literature search revealed that heterocycles containing a dihydro-1,3-oxazine ring system exhibit a wide spectrum of pharmacological activities, for example, acting as antimicrobial [31][32][33], anti-HIV [34], antimalarial [35] or antitumor agents [36][37]. By considering the

• anticancer significance of these two classes of molecules, it was contemplated to construct new dihydro-1,3-oxazinoporphyrins combining the porphyrin and dihydro-1,3-oxazine moieties in a single molecular framework. Such hybrid compounds may prove useful for pharmacological studies or in the development of

Expanding the chemical diversity of spirooxindoles via alkylative pyridine dearomatization

• Chunhui Dai,
• Bo Liang and
• Corey R. J. Stephenson

Beilstein J. Org. Chem. 2012, 8, 986–993, doi:10.3762/bjoc.8.111

• products 8a–c were isolated in moderate yields. Finally, the structure of compound 8a was established by single-crystal X-ray analysis (Figure 3). Conclusion In summary, we developed a practical and efficient method to synthesize spirooxindole derivatives with a [1,3]oxazine fused-ring system. The reaction

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

• hydroxylated 2H-1,2-oxazine derivatives is presented utilizing the [3 + 3] cyclisation of lithiated alkoxyallenes and an L-erythrose-derived N-glycosyl nitrone as precursors. This key step proceeded only with moderate diastereoselectivity, but allowed entry into both enantiomeric series of the resulting 3,6

• ][8], these nitrones very often furnish the corresponding products in a highly selective manner. In this context, reactions of lithiated alkoxyallenes with enantiopure nitrones are particularly of interest since they lead by a [3 + 3] cyclisation process to 1,2-oxazine derivatives with excellent

• reagents [33]. Here we report on the application of a nitrone with an L-erythronolactone-derived auxiliary for the synthesis of 3,6-dihydro-2H-1,2-oxazine derivatives of type D. Their selected transformations, including hydroboration of the enol ether moiety, oxidative work-up, glycosyl cleavage, and

Recent developments in gold-catalyzed cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2011, 7, 1075–1094, doi:10.3762/bjoc.7.124

• ) cycloaddition of related 2-(1-alkynyl)-2-alken-1-ones 10 with nitrones [47]. The reactions provided a very practical entry to bicyclic oxazine derivatives 11, which were obtained in good yields and excellent selectivities (Scheme 5). A plausible mechanism, proposed by the authors, consists of an initial

Predicting the UV–vis spectra of oxazine dyes

• Scott Fleming,
• Andrew Mills and
• Tell Tuttle

Beilstein J. Org. Chem. 2011, 7, 432–441, doi:10.3762/bjoc.7.56

• predict the absorption spectra of a series of oxazine dyes and the effect of solvent on the accuracy of these predictions. Based on the results of this study, it is clear that for the series of oxazine dyes an accurate prediction of the excitation energy requires the inclusion of solvent. Implicit solvent

• ; oxazine; TD-DFT; UV–vis; Introduction Oxazine dyes are a subclass of quinone imines, which are all based upon the p-benzoquinone imine or -diimine scaffold. Other important subclasses within the quinone imines include, the azine dyes and thiazine dyes. The structural relationships described are

• thiazine dyes are metachromatic [4][5], this investigation is limited to the study of oxazine dyes. Oxazine dyes are useful partly because they exhibit solvatochromism, this makes them sensitive to their surrounding environment, and hence they have been utilized in various applications as molecular probes

Palladium- catalyzed cross coupling reactions of 4-bromo- 6H-1,2-oxazines

• Reinhold Zimmer,
• Elmar Schmidt,
• Michal Andrä,
• Marcel-Antoine Duhs,
• Igor Linder and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2009, 5, No. 44, doi:10.3762/bjoc.5.44

• .5.44 Abstract A number of 4-aryl- and 4-alkynyl-substituted 6H-1,2-oxazines 8 and 9 have been prepared in good yields via cross coupling reactions of halogenated precursors 2, which in turn are easily accessible by bromination of 6H-1,2-oxazines 1. Lewis-acid promoted reaction of 1,2-oxazine 9c with 1

• -hexyne provided alkynyl-substituted pyridine derivative 12 thus demonstrating the potential of this approach for the synthesis of pyridines. Keywords: alkyne; halogenation; 1,2-oxazines; palladium catalysis; pyridines; Introduction A broad range of synthetic applications demonstrates that 1,2-oxazine

• with triethylamine (Scheme 1). The 4-bromo-6H-1,2-oxazines were obtained in reasonable to good yields. The bromination of 3-phenyl-substituted 6H-1,2-oxazine 1a often resulted in a mixture of several brominated products which are easily separable by chromatography. Depending on the reaction scale and