Photocycloadditions and photorearrangements

• Axel G. Griesbeck

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

• that use electronic excitation are photocycloadditions and photochemical rearrangements. These reactions have been intensively investigated in recent decades in terms of regio-, stereo-, spin- and (electronic) configurational selectivities. Prior to every photochemical reaction, an electronically

• photocycloaddition, for example, is an important route to oxetanes, products that have recently gained increasing attention as building blocks in organic synthesis as well as in materials science [1]. Photochemical rearrangements are impressive reactions with regard to the generation of complexity: 1,2- and 1,3-acyl

• shifts are known from carbonyl photochemistry, di-π-methane and oxa-di-π-methane rearrangements are processes that can occur with a remarkable increase in molecular and stereochemical complexity, as can meta arene photocycloadditions. It was a great pleasure to act as the editor of this Thematic Series

Highly substituted benzannulated cyclooctanol derivatives by samarium diiodide-induced cyclizations

• Jakub Saadi,
• Irene Brüdgam and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2010, 6, 1229–1245, doi:10.3762/bjoc.6.141

• ][7][8][9][10][11][12][13][14][15][16][17][18]. Successful approaches include ring-closing metathesis [4], rearrangements [5], and cycloadditions [6], transition metal-catalyzed cyclizations [7][8], nucleophilic and electrophilic substitution reactions [9] as well as ring expansion reactions [10

Redox-active tetrathiafulvalene and dithiolene compounds derived from allylic 1,4-diol rearrangement products of disubstituted 1,3-dithiole derivatives

• Filipe Vilela,
• Peter J. Skabara,
• Christopher R. Mason,
• Thomas D. J. Westgate,
• Asun Luquin,
• Simon J. Coles and
• Michael B. Hursthouse

Beilstein J. Org. Chem. 2010, 6, 1002–1014, doi:10.3762/bjoc.6.113

• obtained from the diol includes ketone, aldehyde and haloalkene functionalities and these offer further possibilities for the synthetic use of TTF-based compounds that are well known in conducting materials [5]. Herein, we report an extended study of these unusual 1,4-aryl rearrangements involving 1,3

• -dithiole-2-thione and TTF derivatives, postulate a likely reaction mechanism and comment on substituent effects. Results and Discussion Synthesis Scheme 1 summarises the overall procedure that leads to the 1,4-aryl rearrangements. The lithiation of compound 1 with LDA and subsequent reaction with aryl

• -electron density. The second hydroxy group is eliminated in a dehydration process. Loss of a further proton affords the neutral product 3 with a fully aromatised 6-membered ring. This process bears similarities to other rearrangements that are well known in classical organic chemistry [7][8][9]. The

α,β-Aziridinylphosphonates by lithium amide-induced phosphonyl migration from nitrogen to carbon in terminal aziridines

• David. M. Hodgson and
• Zhaoqing Xu

Beilstein J. Org. Chem. 2010, 6, 978–983, doi:10.3762/bjoc.6.110

• phosphonyl rearrangements (8→9, Scheme 2) were developed by Hammerschmidt and Hanbauer [21], and a stereoretentive N- to C-[1,2]-shift in an α-lithiated pyrrole involving a chiral tert-butyl(phenyl)phosphinyl group has been reported [22]. With regard to previous anion-induced N- to C-1,2-shifts in aziridines

Total synthesis of (±)-coerulescine and (±)-horsfiline

• Mukund G. Kulkarni,
• Attrimuni P. Dhondge,
• Sanjay W. Chavhan,
• Ajit S. Borhade,
• Yunnus B. Shaikh,
• Deekshaputra R. Birhade,
• Mayur P. Desai and
• Nagorao R. Dhatrak

Beilstein J. Org. Chem. 2010, 6, 876–879, doi:10.3762/bjoc.6.103

• include the following oxidative rearrangements: lead tetraacetate [3], sodium tungstate [11], tert-butyl hypochlorite [12] and N-bromosuccinimide [13]. Other approaches involve the Mannich reaction [14], ring expansion reactions [15][16], 1,3-dipolar [3 + 2] cycloadditions [17][18][19], intramolecular

A thermally-induced, tandem [3,3]-sigmatropic rearrangement/[2 + 2] cycloaddition approach to carbocyclic spirooxindoles

• Kay M. Brummond and
• Joshua M. Osbourn

Beilstein J. Org. Chem. 2010, 6, No. 33, doi:10.3762/bjoc.6.33

• complexity. Furthermore, this approach includes a rare example of a thermal [3,3]-sigmatropic rearrangement of a propargylic acetate while metal catalyzed rearrangements of the propargyl acetates are common. Work is currently underway to expand the synthetic utility of this reaction. Experimental

Size selective recognition of small esters by a negative allosteric hemicarcerand

• Holger Staats and
• Arne Lützen

Beilstein J. Org. Chem. 2010, 6, No. 10, doi:10.3762/bjoc.6.10

• single receptor. This causes conformational rearrangements that switch on or off a function that is inherently embedded in the different parts of the molecule but which need to be specially arranged in space in order to act in an optimized cooperative fashion. Some time ago we were able to report on a

A stable enol from a 6-substituted benzanthrone and its unexpected behaviour under acidic conditions

• Marc Debeaux,
• Kai Brandhorst,
• Peter G. Jones,
• Henning Hopf,
• Jörg Grunenberg,
• Wolfgang Kowalsky and
• Hans-Hermann Johannes

Beilstein J. Org. Chem. 2009, 5, No. 31, doi:10.3762/bjoc.5.31

• be explained as follows. For the production of 11 and 12 we propose the mechanism summarised in Scheme 4 [8]. Both 11 and 12 have the same molecular mass as the starting material 4, so the processes leading to these two products are isomerisations. The protonation that initiates the rearrangements

Controlling hazardous chemicals in microreactors: Synthesis with iodine azide

• Johan C. Brandt and
• Thomas Wirth

Beilstein J. Org. Chem. 2009, 5, No. 30, doi:10.3762/bjoc.5.30

• was used, but lower yields (34% yield of 4b) were observed than those given in literature (53–97%) [17]. Maybe the sodium ion acts like a Lewis acid and accelerates the rearrangement. It is known that Lewis acid catalysts such as zinc triflate can accelerate Curtius rearrangements and the sodium

Enantiospecific synthesis of [2.2]paracyclophane- 4-thiol and derivatives

• Gareth J. Rowlands and
• Richard J. Seacome

Beilstein J. Org. Chem. 2009, 5, No. 9, doi:10.3762/bjoc.5.9

• ], sigmatropic rearrangements [21] and as either thiyl radical precursors [22] or as a source of hydrogen in radical chemistry [23]. With the appropriate sulfur derivative, stereoselective variants of all these transformations can be envisaged. Currently, there are few examples of sulfur containing [2.2

Radical cascades using enantioenriched 7-azabenzonorbornenes and their applications in synthesis

• David M. Hodgson and
• Leonard H. Winning

Beilstein J. Org. Chem. 2008, 4, No. 38, doi:10.3762/bjoc.4.38

• -azabenzonorbornadienes. Oxidation (using RuO4) and Birch reduction of the 2-aza-5,6-benzonorbornenes provide access to substituted pyrrolidines and tetrahydroindenes, respectively. Keywords: asymmetric synthesis; deoxygenation; radicals; rearrangements; tandem reactions; Introduction Carbon-centred radicals have been

• is most conveniently achieved by the incorporation of one or more structural directing effect(s). Research in our laboratory has focussed on using the potential dative stabilising effect of an α-nitrogen in the product-producing radical to direct homoallylic radical rearrangements for use in azacycle

• synthesis [14]. The utility of nitrogen-directed radical rearrangements in the 7-azanorbornene system has been reported previously in relation to the synthesis of a variety of biologically-relevant targets, including epibatidine analogues [15][16], kainic acid [17][18] and ibogamine [19]. In these studies

Desymmetrization of 7-azabicycloalkenes by tandem olefin metathesis for the preparation of natural product scaffolds

• Wolfgang Maison,
• Marina Büchert and
• Nina Deppermann

Beilstein J. Org. Chem. 2007, 3, No. 48, doi:10.1186/1860-5397-3-48

• , ring closing metathesis (RCM) and tandem metatheses [10][11][12][13] have been particularly successful strategies for the assembly of common natural product scaffolds. [14][15][16][17][18][19][20][21][22] A general advantage of these approaches is that ring closure and/or scaffold-rearrangements can be

Investigation of acetyl migrations in furanosides

• O. P. Chevallier and
• M. E. Migaud

Beilstein J. Org. Chem. 2006, 2, No. 14, doi:10.1186/1860-5397-2-14

• degradation under such conditions of the synthetic intermediates of compounds 1–5, all incorporating either an acetonide or a methyl ketal moiety. The reactions were stopped as soon as complete disappearance of the starting material had occurred to minimise rearrangements subsequent to the deprotection step

Colchitaxel, a coupled compound made from microtubule inhibitors colchicine and paclitaxel

• Karunananda Bombuwala,
• Thomas Kinstle,
• Vladimir Popik,
• Sonal O. Uppal,
• James B. Olesen,
• Jose Viña and
• Carol A. Heckman

Beilstein J. Org. Chem. 2006, 2, No. 13, doi:10.1186/1860-5397-2-13

• microtubule array. It decreases the tendency of microtubules to be anchored in the microtubule organizing center [57] and causes rearrangement into patterns that are rarely found in untreated cells. Such rearrangements included parallel arrays at the cell edge and focal points in the cytoplasm from which

• , the coupled agent retained some of the effects of the combination of starting agents but had fewer effects on microtubule structure. Future investigation of colchitaxel-treated cells by the shape assay will be useful in determining whether the microtubule rearrangements coincide with the reversal of

Total syntheses of oxygenated brazanquinones via regioselective homologous anionic Fries rearrangement of benzylic O-carbamates

• Glaucia Barbosa Candido Alves Slana,
• Mariângela Soares de Azevedo,
• Rosângela Sabattini Capella Lopes,
• Cláudio Cerqueira Lopes and
• Jari Nobrega Cardoso

Beilstein J. Org. Chem. 2006, 2, No. 1, doi:10.1186/1860-5397-2-1

• construction of these bioactive compounds for future biological evaluation. The emerging carbanionic aromatic chemistry (anionic ortho-Fries, [13] homologous anionic Fries, [14] remote anionic Fries rearrangements [15] and carbamoyl Baker-Venkataraman reaction [16]) originating from the Directed ortho

• metalation groups (DMGs) undergo competitive anionic [1,2] and [1,4] Wittig – carbamoyl rearrangements (paths a and b) [18][19] orientated by the groups R and DMGs (Figure 1). Conceptual combination of path b and the well established tandem DoM route to anthraquinones and heteroanthraquinones [20] led to the

• described. This methodology could be expanded in the future for the construction of new molecules with similar structures. Examples of carbanionic aromatic chemistry rearrangements. Retrosyntheses of Brazanquinones (1). Total syntheses of brazanquinones (1 a-c). Total syntheses of phthalide (9). Supporting

Stereoselective α-fluoroamide and α-fluoro- γ-lactone synthesis by an asymmetric zwitterionic aza-Claisen rearrangement

• Kenny Tenza,
• Julian S. Northen,
• David O'Hagan and
• Alexandra M. Z. Slawin

Beilstein J. Org. Chem. 2005, 1, No. 13, doi:10.1186/1860-5397-1-13

• fluorinated substrates, to generate α-fluoro-γ-vinyl amides and then α-fluoro-γ-lactones as the end products after iodolactonisation. In 1998 Nubbemeyer[12][13] reported on such aza-Claisen rearrangements using the N-allylproline ester 1 and the N-allylpyrrolidine ether 2 with the acid fluoride of azidoacetic