An efficient synthesis of N-substituted 3-nitrothiophen-2-amines

• Sundaravel Vivek Kumar,
• Shanmugam Muthusubramanian,
• J. Carlos Menéndez and
• Subbu Perumal

Beilstein J. Org. Chem. 2015, 11, 1707–1712, doi:10.3762/bjoc.11.185

• assembled from acyclic starting materials by methods such as i) reaction of lithiated 1-alkynes or allenes with substituted phenyl isothiocyanates [20], ii) treatment of N-allylbenzotriazole with substituted phenylisothiocyanates [21] and iii) reaction between phenyl isothiocyanate and electron-deficient

• allenes catalyzed by PPh3 [22] (Scheme 1a–c). On the other hand, studies on the synthesis of 3-nitrothiophenes are scarce. One of the traditional methods involves electrophilic aromatic substitution reactions of thiophenes, which introduces substituents at the 2- and 5-positions, but with some drawbacks

Why base-catalyzed isomerization of N-propargyl amides yields mostly allenamides rather than ynamides

• Armando Navarro-Vázquez

Beilstein J. Org. Chem. 2015, 11, 1441–1446, doi:10.3762/bjoc.11.156

• the yncarbamate 13c. The difference in the N-allenyl → N-alkynyl gap for 12 and 13 could be partially attributed to the different basal conformations adopted by allenes 12b and 13b whereas the methynic proton in the benzylic chain respectively prefers an anti or syn conformation with respect to the N

Synthesis of γ-hydroxypropyl P-chirogenic (±)-phosphorus oxide derivatives by regioselective ring-opening of oxaphospholane 2-oxide precursors

• Iris Binyamin,
• Shoval Meidan-Shani and
• Nissan Ashkenazi

Beilstein J. Org. Chem. 2015, 11, 1332–1339, doi:10.3762/bjoc.11.143

• unique interest from a synthetic point of view due to their ability to create new phosphines [48] or to be involved in various reactions (e.g., [2 + 3] cycloaddition) [49][50]. Moreover, propargyl compounds are known to undergo base catalyzed 1,3-prototropic rearrangments to the corresponding allenes [51

Regioselective synthesis of chiral dimethyl-bis(ethylenedithio)tetrathiafulvalene sulfones

• Flavia Pop and
• Narcis Avarvari

Beilstein J. Org. Chem. 2015, 11, 1105–1111, doi:10.3762/bjoc.11.124

• previously observed only in bismuth wires and carbon nanotubes [13]. Another interesting research area is the redox modulation of the chiroptical properties described in derivatives such as TTF-allenes [14], TTF-helicenes [15], or TTF-paracyclophanes [16]. Thus, to address the different opportunities offered

Chiroptical properties of 1,3-diphenylallene-anchored tetrathiafulvalene and its polymer synthesis

• Masashi Hasegawa,
• Junta Endo,
• Seiya Iwata,
• Toshiaki Shimasaki and
• Yasuhiro Mazaki

Beilstein J. Org. Chem. 2015, 11, 972–979, doi:10.3762/bjoc.11.109

• (ΔG‡ = 180 kJ mol−1 for CH3CH=C=CHCH3) [11]. In contrast, several allenes directly connected with electron-donating groups occasionally underwent photoracemization [12][13]. Although the mechanism of the photoracemization is not clear, a comparative examination of the racemization rate in 1 and 2, the

• of the C=C=C unit at 1914 cm−1. Because new symmetrical allenes were subject to optical resolution, the separation of (rac)-3 was carried out by using a recycling HPLC method on a chiral stationary phase (DAICEL Chiralpak IA-3) with hexane/CHCl3/EtOH (v/v = 20:10:0.2) elution. Thus, equimolecular

• amounts of the optically pure allenes (+)-3 and (−)-3, whose optical rotations ([α]D25) are +726 (c 0.853 in CH2Cl2) and −721(c 0.853 in CH2Cl2), respectively, were collected. Similarly, optical resolution of (rac)-9 also provided (+)/(−)-9 with optical rotations ([α]D25) of +338 (c 0.83 in CH2Cl2) and

Anionic sigmatropic-electrocyclic-Chugaev cascades: accessing 12-aryl-5-(methylthiocarbonylthio)tetracenes and a related anthra[2,3-b]thiophene

• Laurence Burroughs,
• John Ritchie,
• Mkhethwa Ngwenya,
• Dilfaraz Khan,
• William Lewis and
• Simon Woodward

Beilstein J. Org. Chem. 2015, 11, 273–279, doi:10.3762/bjoc.11.31

• eliminations. Structural packing motifs and electronic properties are reported for the tetracenes. Keywords: allenes; anionic Chugaev rearrangement; anionic sigmatropic rearrangement; tetracene properties; X-ray structures; Introduction In recent years polyacenes, especially tetra- and pentacenes, have been

• cascade approach for rapid access to tetracene sulfoxides in 2007 (Scheme 1). In 2012 Liu used a Pd-based strategy to provide 12-substituted 5-aryltetracenes [after final trapping with RB(OH)2)] [16]. Both of these reactions rely on the formation of bis-allenes 2, attained by Lin through 2,3-sigmatropic

• very efficient routes to tetracene derivatives containing one or more thiolate (SH) groups for the use in highly electrically conducting organics. In this regard we were attracted by a single result in the early literature [17] showing that traces of allenes related to 2 (X = SCOSMe) were accessible

Gold(I)-catalysed synthesis of a furan analogue of thiamine pyrophosphate

• Amjid Iqbal,
• El-Habib Sahraoui and
• Finian J. Leeper

Beilstein J. Org. Chem. 2014, 10, 2580–2585, doi:10.3762/bjoc.10.270

• planned synthesis was the formation of the furan ring. Homogeneous gold-catalysed reactions have been used recently in the synthesis of furans from alkynes [13][14][15][16][17][18][19][20]. The ease with which alkynes, allenes and alkenes can be activated by Au(I) catalysts to form carbon–carbon and

Chiral phosphines in nucleophilic organocatalysis

• Yumei Xiao,
• Zhanhu Sun,
• Hongchao Guo and
• Ohyun Kwon

Beilstein J. Org. Chem. 2014, 10, 2089–2121, doi:10.3762/bjoc.10.218

• phosphines possessing various chiral skeletons that have been used in asymmetric nucleophilic organocatalytic reactions, including annulations of allenes, alkynes, and Morita–Baylis–Hillman (MBH) acetates, carbonates, and ketenes with activated alkenes and imines, allylic substitutions of MBH acetates and

• developments in nucleophilic chiral phosphine-catalyzed asymmetric reactions, including annulations of allenes, ketenes, alkynes, and Morita–Baylis–Hillman (MBH) carbonates with activated alkenes and imines, allylic substitution of MBH acetates and carbonates, Michael additions, γ-umpolung additions, and

• variety of methods for enantioselective syntheses of structurally diverse acyclic, carbocyclic, and heterocyclic compounds. 2.1 [3 + 2] Annulation of allenes with activated alkenes Nucleophilic phosphine-catalyzed annulations have been established as very useful tools for the syntheses of carbo- and

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

• the addition of the nucleoside moiety to the C-1 or C-2 carbon atom of the C=C double bond. The three-component reactions of nucleoside-derived (uridine or thymidine) allenes 97, a range of aryl iodides, and 1-adamantylamine was accomplished smoothly under the palladium-catalyzed conditions (Scheme 40

• nucleoside-derived allenes 97 (the uridine example shown), and a number of amines 100 (four equivalents, Scheme 41). The polyfunctional products 101 were obtained with excellent (Z)-stereoselectivity. The authors noticed a pronounced relationship between pKa of the amine and the isolated yield of the product

Allenylphosphine oxides as simple scaffolds for phosphinoylindoles and phosphinoylisocoumarins

• G. Gangadhararao,
• Ramesh Kotikalapudi,
• M. Nagarjuna Reddy and
• K. C. Kumara Swamy

Beilstein J. Org. Chem. 2014, 10, 996–1005, doi:10.3762/bjoc.10.99

• . Interestingly, in the presence of wet trifluoroacetic acid, in addition to phosphinoylisocoumarins, phosphorus-free isocoumarins were also obtained. Key products were characterized by single crystal X-ray crystallography. Keywords: allenes; indoles; isocoumarins; organophosphorus; phosphinoyl-heterocycles

• ; propargyl alcohols; Introduction Allenes, by virtue of cumulative double bonds that facilitate reactions with diverse classes of substrates, are versatile building blocks from a synthetic perspective [1][2]. They are also found in many natural products, pharmaceuticals [3] and molecular materials [4]. Thus

• , over the last decade, allenes have attained a prominent position in organic transformations like cycloaddition, cycloisomerization, base or metal-catalyzed reactions [5][6][7]. In particular, cyclization reaction of allenes has emerged as a valuable tool in developing different methods leading to

Phosphinate-containing heterocycles: A mini-review

• Olivier Berger and
• Jean-Luc Montchamp

Beilstein J. Org. Chem. 2014, 10, 732–740, doi:10.3762/bjoc.10.67

• synthesis of chiral bicyclic phosphinates 23a–k by domino hydrophosphinylation/Michael/Michael reaction was realized by Fourgeaud et al. (Scheme 10) [25]. Several 1-oxa-3-aza-6-phosphabicyclo[3.3.0]octanes derivatives 23a–k were obtained in yields around 70% by reacting allenes 21 with imines 22 derived

Silver and gold-catalyzed multicomponent reactions

• Giorgio Abbiati and
• Elisabetta Rossi

Beilstein J. Org. Chem. 2014, 10, 481–513, doi:10.3762/bjoc.10.46

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

• 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

Gold(I)-catalyzed domino cyclization for the synthesis of polyaromatic heterocycles

• Mathieu Morin,
• Patrick Levesque and
• Louis Barriault

Beilstein J. Org. Chem. 2013, 9, 2625–2628, doi:10.3762/bjoc.9.297

• ; cyclization; gold(I); gold catalysis; heterocycles; regioselectivity; Introduction In the last decade, phosphino and NHC–gold complexes have become prominent catalysts for the addition of nucleophiles to alkenes, alkynes and allenes [1][2][3][4][5][6][7][8][9][10][11]. Owing to the high affinity of gold(I

New developments in gold-catalyzed manipulation of inactivated alkenes

• Michel Chiarucci and
• Marco Bandini

Beilstein J. Org. Chem. 2013, 9, 2586–2614, doi:10.3762/bjoc.9.294

• /AgClO4] (5/15 mol %) furnished corresponding functionalized pyrrolidines in good yields and moderate stereoselectivity (Scheme 22) [58]. The preferred alkene activation versus allenes was recently observed in the cascade 1,3-migration/[2 + 2] cycloaddition of 1,7-enyne benzoates (Scheme 23) [59]. When 83

• challenging metal-assisted nucleophilic manipulation of inactivated unsaturated hydrocarbons. Relative inertness of C=C with respect to alkynes or allenes accounts for this trend. In this scenario [Au(I)] and [Au(III)] catalysis is playing a major role leading to tremendous developments spanning from C

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

• carbophilicity, low oxophilicity and high oxidation potential between gold(I) and gold(III) have shown a unique potential to unveil novel types of chemoselective and stereoselective cycloadditions involving alkynes, allenes or alkenes [24][25][26]. A lot of interest has been directed to the development of these

• enantioselectivity. Cycloadditions initiated by activation of allenes Gold(I) catalysts can efficiently activate allenes in a highly chemoselective way, triggering the formation of allenyl cationic species. Different structures have been proposed to represent these gold-activated allene complexes, including η2

• -complexes (B, B’ and B’’), planar σ-allylic cations C, zwitterionic carbenes C’ or η1-bent allenes C’’ (Figure 2) [48]. In some cases, experimental and theoretical evidence supports the participation of one of those structures, but in many other cases the precise nature of these species remains unknown. The

Synthesis of axially chiral gold complexes and their applications in asymmetric catalyses

• Yin-wei Sun,
• Qin Xu and
• Min Shi

Beilstein J. Org. Chem. 2013, 9, 2224–2232, doi:10.3762/bjoc.9.261

• hydroamination of allenes by using a variety of chiral phosphine–Au(I) complexes [57][58][59][60][61][62][63]. On the other hand, the intramolecular hydroamination of olefins is a more important reaction in organic synthesis and has been widely reported [64][65][66][67][68]. Recently, the enantioselective

An approach towards azafuranomycin analogs by gold-catalyzed cycloisomerization of allenes: synthesis of (αS,2R)-(2,5-dihydro-1H-pyrrol-2-yl)glycine

• Jörg Erdsack and
• Norbert Krause

Beilstein J. Org. Chem. 2013, 9, 1936–1942, doi:10.3762/bjoc.9.229

• -aminoallene 17 is described. The target molecule was synthesized in 13 linear steps from Cbz-protected Garner aldehyde (R)-2 in an overall yield of 2.4%. The approach was first examined in model studies, which afforded the alkylated azafuranomycin derivative 13a in 2.9% yield over 12 steps. Keywords: allenes

• and 9). After these successful model studies, we introduced substituents into the allene which can be removed at a later stage. Treatment of propargyl tosylate 5a with lithium dibromocuprate [57][58][59] or the silylcuprate (PhMe2Si)2CuCNLi2 [60][61] afforded the allenes 6b and 6c with 68 and 77

• -catalyzed cycloisomerization proceeded uneventfully (Scheme 3). Desilylation of allenes 6a and 6b with tetrabutylammonium fluoride trihydrate afforded the α-hydroxyallenes 7a/b in high yield, and these were converted into the aminoallenes 8a/b under standard Mitsunobu conditions (DEAD, PPh3, phthalimide

Gold-catalyzed cyclization of allenyl acetal derivatives

• Dhananjayan Vasu,
• Samir Kundlik Pawar and
• Rai-Shung Liu

Beilstein J. Org. Chem. 2013, 9, 1751–1756, doi:10.3762/bjoc.9.202

• , and assignable to other products including 4g and 4h. The reaction worked well with substrates bearing a different trisubstituted allenes, giving the desired cyclopentenone 4g and 4h in 82–83% yields. The preceding cyclization is mechanistically interesting because it involves a cleavage of the C–H

Homolytic substitution at phosphorus for C–P bond formation in organic synthesis

• Hideki Yorimitsu

Beilstein J. Org. Chem. 2013, 9, 1269–1277, doi:10.3762/bjoc.9.143

• reported that diphenyl(trimethylstannyl)phosphine reacts not only with terminal alkynes but also with internal alkynes and allenes (Scheme 4) [24][25]. It is noteworthy that the regioselectivity of the radical addition to propynamide is opposite to that of the relevant ionic Michael addition. Considering

• studied the photoinduced radical chalcogenophosphination of alkynes and allenes by means of PhCh–ChPh/Ph2P–PPh2 binary systems (Ch = S, Se, Te) [30][37][38][39]. The regioselective outcome of the photoinduced thio- and selenophosphination of terminal alkynes (Table 5) is similar to that of the thermal

• . Thiophosphination with S-thiophosphinyl O-ethyl dithiocarbonate. Photoinduced selenophosphination of allenes. Photoinduced tellurophosphination. Decarboxylative phosphorylation of carboxylic acid derivatives. Plausible mechanism of decarboxylative phosphorylation. Radical phosphination of PTOC esters with white

Gold-catalyzed intermolecular hydroamination of allenes with sulfonamides

• Chen Zhang,
• Shao-Qiao Zhang,
• Hua-Jun Cai and
• Dong-Mei Cui

Beilstein J. Org. Chem. 2013, 9, 1045–1050, doi:10.3762/bjoc.9.117

• the intermolecular hydroamination of allenes with sulfonamides is shown. The reaction proceeded smoothly under mild conditions for differently substituted allenes giving N-allylic sulfonamides in good yields with high regioselectivity and E-selectivity. Keywords: allene; gold catalysis

• ; hydroamination; N-sulfonyl; selectivity; sulfonamide; Introduction Hydroamination of an N–H bond across a C–C unsaturated bond represents one of the most effective and atom-economical methods to prepare amine derivatives [1][2][3][4][5]. In the case of using allenes, this reaction can lead to allylamines, which

• are invaluable precursors for the synthesis of natural products and other potentially biologically relevant substances [6]. In the literature, a wide range of catalytic intramolecular hydroaminations of allenes are known, but only a small number of intermolecular hydroamination reactions are reported

Gold-catalyzed oxycyclization of allenic carbamates: expeditious synthesis of 1,3-oxazin-2-ones

• Benito Alcaide,
• Pedro Almendros,
• M. Teresa Quirós and
• Israel Fernández

Beilstein J. Org. Chem. 2013, 9, 818–826, doi:10.3762/bjoc.9.93

• gold-catalyzed synthetic routes to 1,3-oxazinan-2-ones (kinetically controlled products) and 1,3-oxazin-2-one derivatives (thermodynamically favored) from easily accessible allenic carbamates has been carried out. Keywords: allenes; computational chemistry; gold; gold catalysis; heterocycles; reaction

• are also used as valuable intermediates in organic synthesis [8][9][10][11][12][13][14]. Recently, allenes have attracted much attention as they have been used for the preparation of both biologically relevant drugs as well as advanced materials [15][16][17][18][19][20][21][22][23][24][25][26][27

• ][37][38][39][40][41]. The Boc protective group has been widely used in allene chemistry, being an inert and recommended partner in gold- and palladium-catalyzed aminocyclizations of allenes [42]. On the other hand, reports of gold-catalyzed cyclizations leading to heterocycles that contain more than

Some aspects of radical chemistry in the assembly of complex molecular architectures

• Béatrice Quiclet-Sire and
• Samir Z. Zard

Beilstein J. Org. Chem. 2013, 9, 557–576, doi:10.3762/bjoc.9.61

• , this strategy was applied to a formal synthesis of (±)-hirsutic acid [39]. Access to polycyclic structures can be accomplished by cyclisation of propargyl radicals. Alkynes or allenes can be obtained, depending on the disposition of the internal alkene with respect to the delocalised radical [40][41

• for the xanthate-transfer process. An example is provided in Scheme 25 illustrating a rapid, convergent access to cyclopentanols and to functional allenes. Thus, the xanthate group in adduct 131, derived from the radical addition to vinyl trimethylsilane, can be replaced by a dichlorovinyl motif

• . Construction of a trans-decalin derivative. Multiple uses of a chloroacetonyl xanthate. A convergent route to spiroketals. A modular approach to 3-arylpiperidines. A convergent route to cyclopentanols and to functional allenes. Allylation and vinylation of a xanthate and an iodide. Vinyl epoxides as allylating

Inter- and intramolecular enantioselective carbolithiation reactions

• Asier Gómez-SanJuan,
• Nuria Sotomayor and
• Esther Lete

Beilstein J. Org. Chem. 2013, 9, 313–322, doi:10.3762/bjoc.9.36

• electrophiles to give enantioenriched chiral allenes. By high-resolution control of the residence time, the epimerization of a configurationally unstable chiral organolithium intermediate 23 could be suppressed. Using this method, n-butyllithium reacts with enynes 22 in the presence of chiral ligands, and the

• resulting organolithiums can be trapped with different electrophiles to afford allenes 24 with complete regioselectivity and good yields. The best ee is obtained when there is a carbamoyloxy group (CbO) as directing group in the substrate with (−)-sparteine (L1) as the chiral ligand (Scheme 8) [27]. Despite

Recent advances in transition-metal-catalyzed intermolecular carbomagnesiation and carbozincation

• Kei Murakami and
• Hideki Yorimitsu

Beilstein J. Org. Chem. 2013, 9, 278–302, doi:10.3762/bjoc.9.34

• group; (2) alkynes bearing a directing group; (3) strained cyclopropenes; (4) unactivated alkynes or alkenes; and (5) substrates that have two carbon–carbon unsaturated bonds (allenes, dienes, enynes, or diynes). Keywords: alkene; alkyne; carbomagnesiation; carbometalation; carbozincation; transition

• bearing a directing group; (3) cyclopropenes; (4) unactivated alkynes or alkenes; and (5) substrates that have two carbon–carbon unsaturated bonds (allenes, dienes, enynes, or diynes). Review Carbomagnesiation and carbozincation of electron-deficient alkynes Since conjugate addition reactions of

• -bis(diphenylphosphino)benzene (dppbz) ligand efficiently suppressed the elimination pathway to provide the corresponding carbozincation product 4o in high yield (Scheme 45, reaction 4n to 4o) [132]. Carbomagnesiation and carbozincation of allenes, dienes, enynes, and diynes Interesting transformations