Continuous flow photolysis of aryl azides: Preparation of 3H-azepinones

• Farhan R. Bou-Hamdan,
• François Lévesque,
• Alexander G. O'Brien and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2011, 7, 1124–1129, doi:10.3762/bjoc.7.129

• reaction conditions using the flow reactor allowed minimization of secondary photochemical reactions. Keywords: azepinones; azides; continuous flow; nitrenes; photochemistry; Findings Although photochemical rearrangements are an important class of reactions for heterocycle synthesis [1][2], their use is

• column chromatography. Rearrangements of aryl azides bearing electron withdrawing substituents are better represented in the literature than their electron donating congeners [31], and this was reflected in our compound selection. Methyl 2-azidobenzoate (8b), the corresponding acid 8c and dimethyl 2

Triazole–Au(I) complex as chemoselective catalyst in promoting propargyl ester rearrangements

• Dawei Wang,
• Yanwei Zhang,
• Rong Cai and
• Xiaodong Shi

Beilstein J. Org. Chem. 2011, 7, 1014–1020, doi:10.3762/bjoc.7.115

Recent advances in the gold-catalyzed additions to C–C multiple bonds

• He Huang,
• Yu Zhou and
• Hong Liu

Beilstein J. Org. Chem. 2011, 7, 897–936, doi:10.3762/bjoc.7.103

• intramolecular substrate rearrangements (Scheme 18). 2.4 Propargylic alcohols and propargylic carboxylate rearrangements Pennell et al. reported Meyer–Schuster rearrangements of propargylic alcohols 102 at room temperature in toluene with 1–2 mol % PPh3AuNTf2, in the presence of 0.2 equiv of 4

• . reported a general gold-catalyzed direct oxidative homo-coupling of non-activated arenes 207 (Scheme 38). The reaction protocol tolerates a wide range of functional groups [92]. All halogens survive the reaction, which provides the potential for further reactions. 4.2 Rearrangements and ring enlargement A

• gold-catalyzed rearrangement of 6-alkynylbicyclo[3.1.0]hexen-2-enes 209 has been developed [93]. In this reaction, divergent structural rearrangements are observed in the absence/presence of nucleophiles. The process results in a novel five-to-six-membered ring expansion that involves cleavage of the

Gold-catalyzed propargylic substitutions: Scope and synthetic developments

• Olivier Debleds,
• Eric Gayon,
• Emmanuel Vrancken and
• Jean-Marc Campagne

Beilstein J. Org. Chem. 2011, 7, 866–877, doi:10.3762/bjoc.7.99

• . Direct propargylic substitutions: Scope of nucleophiles. Meyer–Schuster rearrangements. Silyl-protected propargyl alcohols in propargylic substitutions. Acetylacetone as nucleophile in direct propargylic substitution. Enantiomerically enriched propargylic alcohols. Scope of ‘activated’ alcohols in direct

When gold can do what iodine cannot do: A critical comparison

• Sara Hummel and
• Stefan F. Kirsch

Beilstein J. Org. Chem. 2011, 7, 847–859, doi:10.3762/bjoc.7.97

• . Nevertheless, heteroatom nucleophiles having no protons attached react in gold-catalyzed carboalkoxylations [63][64][65][66] and related processes where the analogous electrophilic processes are unknown. Catalyzed propargylic ester rearrangements [67][68] also remain the realm of gold-complexes since such

Isotopic labelling studies for a gold-catalysed skeletal rearrangement of alkynyl aziridines

• Paul W. Davies,
• Nicolas Martin and
• Neil Spencer

Beilstein J. Org. Chem. 2011, 7, 839–846, doi:10.3762/bjoc.7.96

• aziridines into 2,4-disubstituted pyrroles. Two isotopomers of the expected skeletal rearrangement product were identified using 13C-labelling and led to a revised mechanism featuring two distinct skeletal rearrangements. The mechanistic proposal has been rationalised against the reaction of a range of 13C

• the most common fundamental steps in these skeletal rearrangements involves C–C bond fission through 1,2-migration. This step is triggered by the generation of carbocationic character, which is generally stabilised in some form, either by an adjacent gold atom or through extended delocalisation. While

• , and hence the isotopomeric reaction selectivity, is controlled by the relative ability of the substituents to stabilise the respective cations in favour of a particular pathway. The observed skeletal rearrangements are consistent with either a 1,2-aryl shift or a 1,2-(metal-stabilised)-vinyl shift in

Highly efficient gold(I)-catalyzed Overman rearrangement in water

• Dong Xing and
• Dan Yang

Beilstein J. Org. Chem. 2011, 7, 781–785, doi:10.3762/bjoc.7.88

• have been used for different types of [3,3]-sigmatropic rearrangements [14][15], only Pd(II) and Hg(II) salts have found wide application in Overman rearrangements. In recent years, gold catalysts have been successfully applied to a series of [3,3]-sigmatropic rearrangements, such as the rearrangement

Synthetic applications of gold-catalyzed ring expansions

• David Garayalde and
• Cristina Nevado

Beilstein J. Org. Chem. 2011, 7, 767–780, doi:10.3762/bjoc.7.87

• on transition metal promoted rearrangements of bicyclo[1.1.0]butanes [11]. Thus Ru–carbonyl complexes promote the rearrangement of 1,2,2-trimethylbicyclo[1.1.0]butane (1) to yield diene 2 and the cyclopropyl derivative 3 (Scheme 1, reaction 1: a,b for 2 and 3), whilst pentafluorophenylcopper tetramer

• into the angular triquinane ventricosene in six steps (Scheme 23). 6 Ring expansions involving propargyl acyloxy rearrangements Propargyl carboxylates 80 can be π-activated by gold towards 1,2-acyloxy migration and/or [3,3]-sigmatropic rearrangement. Two different, but mechanistically related

• organic chemist. Transition metal promoted rearrangements of bicyclo[1.1.0]butanes. Gold-catalyzed rearrangements of strained rings. Gold-catalyzed ring expansions of cyclopropanols and cyclobutanols. Mechanism of the cycloisomerization of alkynyl cyclopropanols and cyclobutanols. Proposed mechanism for

When cyclopropenes meet gold catalysts

• Frédéric Miege,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2011, 7, 717–734, doi:10.3762/bjoc.7.82

• secondary benzylic cyclopropyl cation). The gold carbene 31 was captured by the aromatic group at C3 via an intramolecular Friedel–Crafts reaction. Subsequent elimination of AcOH from compound 33 then delivered methylene indene 30 (Scheme 14) [21]. Other gold-catalyzed rearrangements of cyclopropenes that

The arene–alkene photocycloaddition

• Ursula Streit and
• Christian G. Bochet

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

• photocycloaddition followed by rearrangements. Stable [2 + 2] photocycloadducts. Ortho photocycloadditions with alkynes. Intramolecular ortho photocycloaddition and rearrangement thereof. Intramolecular ortho photocycloaddition to access propellanes. Para photocycloaddition with allene. Photocycloadditions of

An overview of the key routes to the best selling 5-membered ring heterocyclic pharmaceuticals

• Marcus Baumann,
• Ian R. Baxendale,
• Steven V. Ley and
• Nikzad Nikbin

Beilstein J. Org. Chem. 2011, 7, 442–495, doi:10.3762/bjoc.7.57

Molecular rearrangements of superelectrophiles

• Douglas A. Klumpp

Beilstein J. Org. Chem. 2011, 7, 346–363, doi:10.3762/bjoc.7.45

• reactive intermediates may also undergo a wide variety of rearrangement-type reactions. Superelectrophilic rearrangements are often driven by charge–charge repulsive effects, as these densely charged ions react so as to maximize the distances between charge centers. These rearrangements involve reaction

• steps similar to monocationic rearrangements, such as alkyl group shifts, Wagner–Meerwein shifts, hydride shifts, ring opening reactions, and other skeletal rearrangements. This review will describe these types of superelectrophilic reactions. Keywords: dication; rearrangement; superacid

• superelectrophiles are often densely charged species, they are also known for their tendencies to undergo rearrangement and charge migration reactions. These types of conversions will be examined in this review article, including ring opening reactions, carbon–carbon bond shifts, skeletal rearrangements, and charge

Rh-Catalyzed rearrangement of vinylcyclopropane to 1,3-diene units attached to N-heterocycles

• Franca M. Cordero,
• Carolina Vurchio,
• Stefano Cicchi,
• Armin de Meijere and
• Alberto Brandi

Beilstein J. Org. Chem. 2011, 7, 298–303, doi:10.3762/bjoc.7.39

• -annelated heterocyclic compounds [35], we started to investigate some metal-catalyzed rearrangements. The first choice was the readily available so-called Wilkinson catalyst Rh(PPh3)3Cl, because of its documented efficiency in catalyzing the rearrangement [26] and of the possibility to extend its use to

• other interesting transformations, such as the [5 + 2] cycloadditions of vinylcyclopropanes to alkynes developed by Wender and co-workers [36][37]. It is known, that rhodium-catalyzed rearrangements of unactivated VCPs, without any functional substituent, usually afford dienes. In order to evaluate the

• temperatures. This explains the low isolated yields in their syntheses. Analogously to other Rh(I)-catalyzed VCP rearrangements [46][47], the mechanism of the rearrangement likely involves insertion of the Rh(I) species into the cyclopropane ring of the VCP system, with or without incorporation of the double

Effects of anion complexation on the photoreactivity of bisureido- and bisthioureido-substituted dibenzobarrelene derivatives

• Heiko Ihmels and
• Jia Luo

Beilstein J. Org. Chem. 2011, 7, 278–289, doi:10.3762/bjoc.7.37

• unit. Stereoselective DPM rearrangements of dibenzobarrelene derivatives have been reported in special media, such as chiral mesoporous silica [31] or ionic-liquids [32]; however, most examples for stereoselective DPM rearrangements of dibenzobarrelene derivatives have been observed in the solid-state

• asymmetric photoreactions have been conducted with remarkable enantioselectivity in homogeneous solution, whereas reports of asymmetric di-π-methane rearrangements in solutions are relatively rare. Chiral auxiliaries attached as ester or amide functionalities at the vinylic positions of dibenzobarrelene

• induce only low enantioselectivities in the DPM rearrangement in solution [37]; and the ionic auxiliary strategy, which generates impressive enantioselectivity in the solid-state, fails to induce any stereoselectivity in DPM rearrangements in solution. Considering these observations, it remains a

Synthesis of cationic dibenzosemibullvalene-based phase-transfer catalysts by di-π-methane rearrangements of pyrrolinium-annelated dibenzobarrelene derivatives

• Heiko Ihmels and
• Jia Luo

Beilstein J. Org. Chem. 2011, 7, 119–126, doi:10.3762/bjoc.7.17

• these cases, the dibenzosemibullvalene structure was indicated by the characteristic 1H NMR spectroscopic shifts of the 4b-H and 8b-H protons. It has been demonstrated with several examples that solid-state photoreactions are an excellent tool to induce highly selective di-π-methane rearrangements of

• dibenzobarrelene derivatives 2a–g. Di-π-methane rearrangements of dibenzobarrelene derivatives 2a–f (counter ions omitted for clarity). Di-π-methane rearrangement of dibenzobarrelene derivative 2g. Synthesis and solid-state photoreactivity of the sulfonate salt 2b-4. Phase-transfer catalyzed alkylation reactions

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