Asymmetric Diels–Alder reaction with >C=P– functionality of the 2-phosphaindolizine-η¹-P-aluminium(O-menthoxy) dichloride complex: experimental and theoretical results

• Rajendra K. Jangid,
• Nidhi Sogani,
• Neelima Gupta,
• Raj K. Bansal,
• Moritz von Hopffgarten and
• Gernot Frenking

Beilstein J. Org. Chem. 2013, 9, 392–400, doi:10.3762/bjoc.9.40

• experimentally the InCl3-catalyzed cycloisomerisation of 1,6-enynes and demonstrated InCl2+ to be the actual catalytic species participating in the reaction. In this context, it has been emphasized that identifying the real catalytic species may be very challenging, because in many cases impurities in the

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

• intermediates before they decompose [22][23][24][25]. Thus, Yoshida [26] demonstrated that the addition of aryllithiums, generated by halogen–lithium exchange, to conjugated enynes bearing an appropriate directing group occurs with complete regioselectivity and in good yields. More recently, they applied this

• concept to avoid the epimerization of reactive intermediates, which has allowed them to carry out the enantioselective version of the above procedure. Thus, the use of a flow microreactor system has allowed the enantioselective carbolithiation of conjugated enynes, followed by the reaction with

• 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

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

Highly stereocontrolled synthesis of trans-enediynes via carbocupration of fluoroalkylated diynes

• Tsutomu Konno,
• Misato Kishi and
• Takashi Ishihara

Beilstein J. Org. Chem. 2012, 8, 2207–2213, doi:10.3762/bjoc.8.249

• yield. Additionally, such a partial decomposition of 4a was also observed even when 4a was kept in a freezer. With the thus-obtained optimum reaction conditions, we next investigated the β-elimination reaction of various enynes as described in Table 2. As shown in Table 2, entry 2, changing a phenyl

• . Finally, the thus-obtained iodide underwent a smooth Sonogashira cross-coupling reaction to afford the various desired trans-enediyne derivatives in high yields. trans-Enediyne. Regio- and stereoisomers. Synthetic strategy for the preparation of trifluoromethylated diynes. Preparation of various enynes. A

• proposed reaction mechanism. Synthesis of trans-enediynes. aDetermind by 19F NMR. Values in parentheses are of isolated yield. Investigation of the reaction conditions. β-Elimination of various enynes. Investigation of the reaction conditions in carbocupration. Carbocupration with various cuprates

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

Beilstein J. Org. Chem. 2012, 8, 1936–1998, doi:10.3762/bjoc.8.225

Iridium-catalyzed intramolecular [4 + 2] cycloadditions of alkynyl halides

• Andrew Tigchelaar and
• William Tam

Beilstein J. Org. Chem. 2012, 8, 1765–1770, doi:10.3762/bjoc.8.201

• possible by making use of other metal complexes such as Pd [21][22] and Co [23][24][25], but recent advances in iridium chemistry have expanded the scope of the metal complexes that can be used. Common Ir-catalyzed cycloadditions include [2 + 2 + 2] cycloadditions of diynes [11][12][13] or enynes [16] with

• alkynes, [2 + 2 + 2] cyclotrimerizations of alkynes [14][15], and Pauson–Khand-type [2 + 2 + 1] cycloadditions of enynes [17][18][19] and allenynes [20]; however, Ir-catalyzed [4 + 2] cycloadditions are rare in the literature [26][27]. Transition-metal-catalyzed (TMC) [4 + 2] cycloadditions are an

•  2, type 2). The most extensive studies done on alkynyl halides in TMC reactions are on cross-coupling reactions that proceed by oxidative insertion of the metal into the carbon–halide bond (type 1), and these types of reactions have been used to synthesize building blocks, such as enynes [38][39

Synthesis of axially chiral oxazoline–carbene ligands with an N-naphthyl framework and a study of their coordination with AuCl·SMe₂

• Feijun Wang,
• Shengke Li,
• Mingliang Qu,
• Mei-Xin Zhao,
• Lian-Jun Liu and
• Min Shi

Beilstein J. Org. Chem. 2012, 8, 726–731, doi:10.3762/bjoc.8.81

• papers of relevance. Tomioka and co-workers disclosed the first chiral NHC–Au(I) complex 1 (Figure 1), which was applied to catalyze the asymmetric cyclization of 1,6-enynes giving the corresponding cyclopentane derivatives with moderate enantioselectivity up to 59% [9][10]. Iglesias and co-workers

• chiral NHC–Au(I) complexes (4–6) with a binaphthyl or biphenyl framework [13][14]. These Au(I) complexes were applied to catalyze the asymmetric cyclization of 1,6-enynes or allene in up to 70% ee, and the asymmetric intramolecular hydroamination of allene in up to 44% ee. We previously reported a novel

Sonogashira–Hagihara reactions of halogenated glycals

• Dennis C. Koester and
• Daniel B. Werz

Beilstein J. Org. Chem. 2012, 8, 675–682, doi:10.3762/bjoc.8.75

• good to excellent (72% to 92%). Aromatic as well as aliphatic alkynes could be employed for this reaction leading to excellent results. Fluorinated alkynyl-C-glycosides (Table 1, entry 4) may be readily functionalized at the aromatic core, whereas TMS-protected enynes (Table 1, entry 6) allow for

• enynes was achieved by selective reduction of the triple bond by making use of Raney nickel (Table 3). We found that the electron-rich enol ether moiety remains untouched, when reaction times of less than four hours were chosen in the case of the enynes 9e–9h. It should be noted that methanol was a

• also the sterically encumbered TIPS groups render the reduction of the olefinic moiety much more difficult. In contrast to the other enynes the carbohydrate derivative 11a was fully reduced in a diastereoselective manner and in excellent yield to the pyran 14d by employing Pearlman’s catalyst (rt

Combination of gold catalysis and Selectfluor for the synthesis of fluorinated nitrogen heterocycles

• Antoine Simonneau,
• Pierre Garcia,
• Jean-Philippe Goddard,
• Virginie Mouriès-Mansuy,
• Max Malacria and
• Louis Fensterbank

Beilstein J. Org. Chem. 2011, 7, 1379–1386, doi:10.3762/bjoc.7.162

• hydrofluorination of alkynes catalyzed by N-heterocyclic carbene gold(I) complexes [4], or by fluorodeauration of transient vinyl gold species [5][6], has been previously reported in the literature. On the basis of our recent results on the gold-catalyzed cyclization of enynes [7][8][9][10] and allenylhydrazones

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

• migration to give the ring-expanded products 22, formally (4 + 2) cycloadducts. Interestingly, the stereoselectivity of these products is different from that of the thermal Diels–Alder adducts that result when the substrates are heated under reflux in toluene. The use of 1-aryl-1,6-enynes such as 23 and

• ]. Gold-catalyzed intramolecular (4 + 2) cycloadditions of unactivated alkynes and dienes [55]. Gold-catalyzed preparation of bicyclo[4.3.0]nonane derivatives from dienol silyl ethers [59]. Gold(I)-catalyzed intramolecular (4 + 2) cycloadditions of arylalkynes or 1,3-enynes with alkenes [60]. Gold(I

• )-catalyzed intermolecular (2 + 2) cycloaddition of alkynes with alkenes [62]. Metal-catalyzed cycloaddition of alkynes tethered to cycloheptatriene [65]. Gold-catalyzed cycloaddition of functionalized ketoenynes: Synthesis of (+)-orientalol F [68]. Gold-catalyzed intermolecular cyclopropanation of enynes

Asymmetric Au-catalyzed cycloisomerization of 1,6-enynes: An entry to bicyclo[4.1.0]heptene

• Alexandre Pradal,
• Chung-Meng Chao,
• Patrick Y. Toullec and
• Véronique Michelet

Beilstein J. Org. Chem. 2011, 7, 1021–1029, doi:10.3762/bjoc.7.116

• gold-catalyzed cycloisomerization reaction of heteroatom tethered 1,6-enynes is described. The cycloisomerization reactions were conducted in the presence of the chiral cationic Au(I) catalyst consisting of (R)-4-MeO-3,5-(t-Bu)2-MeOBIPHEP-(AuCl)2 complex and silver salts (AgOTf or AgNTf2) in toluene

• under mild conditions to afford functionalized bicyclo[4.1.0]heptene derivatives. The reaction conditions were found to be highly substrate-dependent, the best results being obtained in the case of oxygen-tethered enynes. The formation of bicyclic derivatives, including cyclopropyl pentasubstituted ones

• , was reported in moderate to good yields and in enantiomeric excesses up to 99%. Keywords: asymmetric catalysis; bicycloheptene; cycloisomerization reactions; enynes; gold; Introduction Metal-catalyzed cycloisomerization reactions of 1,n-enynes have emerged as efficient processes that contribute to

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

• chirality transfer. Rüttinger et al. reported a gold-catalyzed synthetic route for the preparation of enynes (Scheme 4) [26]. The gold-catalyzed cyclization provided the corresponding exo-enol ethers 19 in moderate to high yield with complete regioselectivity. By contrast, Wilckens et al. reported the gold

• under mild conditions. Toste’s group reported a gold(I)-catalyzed sequential cycloisomerization/sp3 C–H bond functionalization (Scheme 39) of 1,5-enynes 218 and 1,4-enallenes to yield tetracyclododecane 219 and tetracyclotridecane derivatives, respectively [97]. These transformations represent rare

• + 2] cycloaddition product in very good yield (Scheme 41). Enynes [110][111][112][113][114][115][116], diynes [117][118][119][120], allenynes [121][122][123][124][125][126][127][128], and dienes [129][130][131] are common substrates for intramolecular cycloaddition reactions. Porcel et al. found that

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

• displays the possibility of diverse product creation through the use of either gold- or iodonium-triggered heterocyclizations. Carbocyclizations with 1,5-enynes Within the rapidly developing area of gold-catalysis, enyne cycloisomerizations have been particularly well studied [76][77][78][79][80][81][82

• ][83]. With an appropriate substitution pattern, both 1,5- and 1,6-enynes can be transformed into a broad array of product scaffolds. The corresponding electrophilic transformations are far less developed. With the exception of an early report by Barluenga and co-workers [84], iodonium-induced

• carbocyclizations have been mainly restricted to the intramolecular arylation of alkynes (i.e., arene nucleophiles) [85][86][87][88] whilst simple olefins have been rarely used in this way. Analogous cyclization modes Several processes involving the cycloisomerization of 1,5-enynes have been realized in an

Homoallylic amines by reductive inter- and intramolecular coupling of allenes and nitriles

• Peter Wipf and
• Marija D. Manojlovic

Beilstein J. Org. Chem. 2011, 7, 824–830, doi:10.3762/bjoc.7.94

• to achieve the carbalumination of 1-alkynes [10], internal alkynes [11], conjugated enynes [12], and 1-iodoalkynes [13]. Huang and Pi found that allylzirconocenes underwent conjugated addition to enones in the presence of CuBr·SMe2 [14]. Wipf and Pierce demonstrated that, upon the addition of a zinc

Au(I)/Au(III)-catalyzed Sonogashira-type reactions of functionalized terminal alkynes with arylboronic acids under mild conditions

• Deyun Qian and
• Junliang Zhang

Beilstein J. Org. Chem. 2011, 7, 808–812, doi:10.3762/bjoc.7.92

• mild conditions has been developed. Keywords: arylboronic acid; gold-catalysis; Sonogashira cross-coupling; Introduction The Sonogashira reaction has become the most important and widely used method for the synthesis of arylalkynes and conjugated enynes, which are precursors for natural products

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

• utility of the method can be easily recognized by an examination of the structure of natural products such as repraesentin F, whose core largely comprises the structural motifs generated in this gold-catalyzed cascade. 5 Ring expansions involving enynes The gold-catalyzed heteroatom-assisted 1,2-shift

• already summarized in section 1 of this review, can offer further synthetic potential in combination with 1,6-enyne substrates. Echavarren successfully developed a gold-catalyzed Prins cyclization of enynes 70 to afford trans- and cis-octahydrocyclobuta[a]pentalene skeletons 71 and 72, respectively

• aziridines. Gold-catalyzed synthesis of disubstituted cyclohexadienes. Gold-catalyzed synthesis of indenes. Gold-catalyzed [n + m] annulation processes. Gold-catalyzed generation of 1,4-dipoles. Gold-catalyzed synthesis of repraesentin F. Gold-catalyzed ring expansion of cyclopropyl 1,6-enynes. Gold

A racemic formal total synthesis of clavukerin A using gold(I)-catalyzed cycloisomerization of 3-methoxy-1,6-enynes as the key strategy

• Jae Youp Cheong and
• Young Ho Rhee

Beilstein J. Org. Chem. 2011, 7, 740–743, doi:10.3762/bjoc.7.84

• compatible with the acid-sensitive functional group. Further application of the gold(I)-catalyzed cycloisomerization reaction of 3-methoxy-1,6-enynes to the enantioselective synthesis of more structurally complex cycloheptane natural products is in progress, and will be reported in due course. Retrosynthetic

Synthesis of chiral mono(N-heterocyclic carbene) palladium and gold complexes with a 1,1'-biphenyl scaffold and their applications in catalysis

• Lian-jun Liu,
• Feijun Wang,
• Wenfeng Wang,
• Mei-xin Zhao and
• Min Shi

Beilstein J. Org. Chem. 2011, 7, 555–564, doi:10.3762/bjoc.7.64

• reported in 1989 [71], a variety of neutral or cationic NHC–Au complexes has been synthesized and applied in many catalytic reactions [72][73]. For example, recently, NHC–Au showed good catalytic activity in the intramolecular [4 + 2] cycloadditions of 1,3-enynes or arylalkynes [74], rearrangement of

Rh(I)-catalyzed intramolecular [2 + 2 + 1] cycloaddition of allenenes: Construction of bicyclo[4.3.0]nonenones with an angular methyl group and tricyclo[6.4.0.0^1,5]dodecenone

• Fuyuhiko Inagaki,
• Naoya Itoh,
• Yujiro Hayashi,
• Yumi Matsui and
• Chisato Mukai

Beilstein J. Org. Chem. 2011, 7, 404–409, doi:10.3762/bjoc.7.52

• carbonylative [2 + 2 + 1] cycloaddition of allenenes was developed to prepare bicyclo[4.3.0]nonenones possessing a methyl group at the ring junction, which is difficult to achieve by the Pauson–Khand reaction of the corresponding enynes. This method also provided a new procedure for the construction of the

• %) under a CO atmosphere) provided the ring-closing product 8a in 75% yield (Table 1, entry 3). It has already been shown that the Rh(I)-catalyzed Pauson–Khand type reaction (PKTR) of enynes under a low CO pressure [26][27] leads to better results. Thus, the ring-closing reaction of 7a was performed under

Ene–yne cross-metathesis with ruthenium carbene catalysts

• Cédric Fischmeister and
• Christian Bruneau

Beilstein J. Org. Chem. 2011, 7, 156–166, doi:10.3762/bjoc.7.22

• The positive influence of ethylene in metathesis in the presence of ruthenium catalysts was first evidenced by Mori during the intramolecular ring closing metathesis of enynes [83]. The excess of ethylene would favor the formation of ruthenium methylidene intermediates, and thus prevent catalyst

New library of aminosulfonyl-tagged Hoveyda–Grubbs type complexes: Synthesis, kinetic studies and activity in olefin metathesis transformations

• Etienne Borré,
• Frederic Caijo,
• Christophe Crévisy and
• Marc Mauduit

Beilstein J. Org. Chem. 2010, 6, 1159–1166, doi:10.3762/bjoc.6.132

• catalysts was investigated with various substrates in ring-closing metathesis of dienes or enynes and cross metathesis. The results demonstrate that these catalysts show a good tolerance to various chemical functions. Keywords: cross-metathesis; kinetic studies; olefin metathesis; RCM; ruthenium

• weak influence on the behaviour of the catalysts in these cases. Finally, the reactivity profiles of 4a and 4g were compared in various metathesis reactions in order to evaluate the influence of the NHC ligand. The last point of our study was the comparison between catalysts in RCM of dienes or enynes

Synthesis of fluorinated δ-lactams via cycloisomerization of gem-difluoropropargyl amides

• Satoru Arimitsu and
• Gerald B. Hammond

Beilstein J. Org. Chem. 2010, 6, No. 48, doi:10.3762/bjoc.6.48

• diverse suite of δ-lactams because enynes are suitable partners in ring-closing metathesis reactions or cycloisomerizations. An additional benefit of using enynes in metathesis reactions is that the resulting diene product could be further elaborated using a Diels–Alder reaction to construct bi- or

• to other fluorinated 1,7-enynes we isolated the desired lactams (entries 1–3, Table 2). Higher temperatures were required with internal alkynes (entries 2–5, Table 2), where isomerization occurs and the enyne ester 1d did not yield satisfactory results. Interestingly, although enyne ketone 1e gave a

• reaction of fluorinated 1,7-enynes does not permit substitution at the 6-position of the resultant gem-difluoroisoquinolinone (eq 1, Scheme 2), we examined a potential cross metathesis–enyne metathesis tandem-type reaction (CM–EYM reaction). In theory, if the terminal vinyl group of diene 2 can be modified

The use of silicon- based tethers for the Pauson- Khand reaction

• Adrian P. Dobbs,
• Ian J. Miller and
• Saša Martinović

Beilstein J. Org. Chem. 2007, 3, No. 21, doi:10.1186/1860-5397-3-21

• . Saigo reported that the attempted P-K cyclisation of a variety of 3-sila-1,7-enynes underwent cycloisomerisation instead of the cycloaddition (Scheme 1).[7] Saigo's work showed that this cycloisomersiation was only applicable to 3-sila-1,7-enynes and any other chain length would undergo decomposition