Unpredictable cycloisomerization of 1,11-dien-6-ynes by a common cobalt catalyst

• Abdusalom A. Suleymanov,
• Dmitry V. Vasilyev,
• Valentin V. Novikov,
• Yulia V. Nelyubina and
• Dmitry S. Perekalin

Beilstein J. Org. Chem. 2017, 13, 639–643, doi:10.3762/bjoc.13.62

• development of well-defined catalysts is desirable for further progress. Keywords: catalysis; cobalt; cyclization; enynes; ligands; Introduction Metal-catalyzed reactions of enynes represent an atom- and step-economical route to complex organic molecules with a broad range of functionalities [1][2][3][4

• ]. In particular, cycloisomerization of enynes allows one to prepare compounds with exocyclic double bonds and cyclopropanes in a highly selective manner [5][6][7]. While catalytic transformations of enynes have been investigated in detail, there are only a few examples of similar reactions of dienynes

Chiral cyclopentadienylruthenium sulfoxide catalysts for asymmetric redox bicycloisomerization

• Barry M. Trost,
• Michael C. Ryan and
• Meera Rao

Beilstein J. Org. Chem. 2016, 12, 1136–1152, doi:10.3762/bjoc.12.110

• asymmetric redox bicycloisomerization of 1,6- and 1,7-enynes. This complex was used to synthesize a broad array of [3.1.0] and [4.1.0] bicycles. Sulfonamide- and phosphoramidate-containing products could be deprotected under reducing conditions. Catalysis performed with enantiomerically enriched propargyl

• reactions [8]. They serendipitously discovered that palladium(II) salts catalyzed the cyclization of 1,6-enynes at much lower temperatures compared to the thermal process [9], which normally requires temperatures in excess of 200 °C (Scheme 1, path a). More recently, the same research group disclosed a CpRu

• simple 1,6-enynes displayed a broader scope than Mikami’s palladium system, although none of the examples contained a quaternary stereocenter [25]. Asymmetric enyne cycloisomerization reactions can be extended beyond the construction of 1,4-dienes, depending on the transition metal used and the adjacent

Recent advances in metathesis-derived polymers containing transition metals in the side chain

• Ileana Dragutan,
• Valerian Dragutan,
• Bogdan C. Simionescu,
• Albert Demonceau and
• Helmut Fischer

Beilstein J. Org. Chem. 2015, 11, 2747–2762, doi:10.3762/bjoc.11.296

• allowed the intramolecular cycloisomerization of enynes with high yields and turnover numbers. Copper-containing polymers A copper(I) complex containing a norbornene substituted with the 2-(pyridin-2-yl)-1H-benzimidazole ligand, 44, developed by Il'icheva et al. [64], came to the attention of the

Enantioselective additions of copper acetylides to cyclic iminium and oxocarbenium ions

• Jixin Liu,
• Srimoyee Dasgupta and
• Mary P. Watson

Beilstein J. Org. Chem. 2015, 11, 2696–2706, doi:10.3762/bjoc.11.290

• subsequent trapping by either EtOH or H2O. With respect to the substrate scope, addition of arylalkynes proceeds in high yields and ee’s, including those with some heteroaryl groups (37). Enynes can also be added, but result in lower yields and ee’s, as do octyne and methyl propriolate. A variety of

Recent advances in copper-catalyzed asymmetric coupling reactions

• Fengtao Zhou and
• Qian Cai

Beilstein J. Org. Chem. 2015, 11, 2600–2615, doi:10.3762/bjoc.11.280

• terminal alkynes The catalytic enantioselective allylic alkylation of alkynyl nucleophiles is a powerful tool for the preparation of 1,4-enynes, which are versatile synthetic intermediates in asymmetric organic synthesis [82]. In 2014, Sawamura et al. [83] successfully developed a highly enantioselective

• allylic alkylation of terminal alkynes with primary allylic phosphates through a copper/NHC chiral catalyst system. The authors obtained chiral enynes with a tertiary stereocenter at the allylic propargylic position in good yield and with excellent enantioselectivity (Scheme 35). Conclusion Copper

Copper-catalyzed asymmetric conjugate addition of organometallic reagents to extended Michael acceptors

• Thibault E. Schmid,
• Sammy Drissi-Amraoui,
• Christophe Crévisy,
• Olivier Baslé and
• Marc Mauduit

Beilstein J. Org. Chem. 2015, 11, 2418–2434, doi:10.3762/bjoc.11.263

• cuprates was investigated onto different Michael acceptors [7]. The reaction of dienones such as 6 (Miginiac) [8], enynones of the type 8 (Hulce) [9] or polarized enynes 10 (Krause) [10] consistently proceeded with a 1,6-selectivity, as compounds 7, 9 and 11 were respectively identified as the major

Recent developments in copper-catalyzed radical alkylations of electron-rich π-systems

• Kirk W. Shimkin and
• Donald A. Watson

Beilstein J. Org. Chem. 2015, 11, 2278–2288, doi:10.3762/bjoc.11.248

• -pot procedure, enynes could be synthesized by introducing a second alkyne and a palladium catalyst to perform a tandem carbohalogenation/Sonagashira coupling. Conclusion Copper catalysis has recently emerged as a new means of harnessing the potential of alkyl radicals in catalytic alkylation chemistry

Evidencing an inner-sphere mechanism for NHC-Au(I)-catalyzed carbene-transfer reactions from ethyl diazoacetate

• Manuel R. Fructos,
• Juan Urbano,
• M. Mar Díaz-Requejo and
• Pedro J. Pérez

Beilstein J. Org. Chem. 2015, 11, 2254–2260, doi:10.3762/bjoc.11.245

• skeletal rearrangement of the [2 + 2] cycloaddition of 1,6-enynes [4] is shown in Scheme 1, where three different gold–carbene intermediates are involved in the possible transformations. A different reaction in which the formation of gold–carbene intermediates has been proposed arises from the interaction

• -enynes that involves gold–carbene intermediates. The catalytic activity of IPrAuCl + NaBArF4 in the carbene-transfer reaction to styrene or methanol. The gold-promoted decarbenation reaction described by Echavarren and co-workers. (a) General representation of the metal-catalyzed carbene-transfer

Latent ruthenium–indenylidene catalysts bearing a N-heterocyclic carbene and a bidentate picolinate ligand

• Thibault E. Schmid,
• Florian Modicom,
• Adrien Dumas,
• Etienne Borré,
• Loic Toupet,
• Olivier Baslé and
• Marc Mauduit

Beilstein J. Org. Chem. 2015, 11, 1541–1546, doi:10.3762/bjoc.11.169

• 96% yields, respectively. Interestingly, the more sterically-demanding diene 10 afforded the trisubstituted olefin cyclized product with high 93% isolated yield. Catalyst 4a was also efficient regarding the cyclization of enynes 12 and 14 and the desired diene products were obtained with 89 and 90

Selected synthetic strategies to cyclophanes

• Sambasivarao Kotha,
• Mukesh E. Shirbhate and
• Gopalkrushna T. Waghule

Beilstein J. Org. Chem. 2015, 11, 1274–1331, doi:10.3762/bjoc.11.142

• ) using the McMurry coupling (Figure 8). Pd(0)-catalyzed cross-coupling reaction: In 1997, Yamamoto and co-workers [122] have synthesized the exomethylene paracyclophane 108 via intramolecular benzannulation of conjugated enynes in the presence of palladium(0). In this regard, dibromoalkane 103 was

Relay cross metathesis reactions of vinylphosphonates

• Raj K. Malla,
• Jeremy N. Ridenour and
• Christopher D. Spilling

Beilstein J. Org. Chem. 2014, 10, 1933–1941, doi:10.3762/bjoc.10.201

• intermediacy of an additional terminal alkene 11 (Scheme 3) [19][20][21]. Similarly, Hansen and Lee employed an allyl ether to activate enynes toward cross metathesis [22]. Furthermore, there are several examples of vinylphosphonates participating in ring closing metathesis (RCM) reactions [23][24][25

Preparation of phosphines through C–P bond formation

• Iris Wauters,
• Wouter Debrouwer and
• Christian V. Stevens

Beilstein J. Org. Chem. 2014, 10, 1064–1096, doi:10.3762/bjoc.10.106

• was obtained. Several butadiene derivatives were synthesized by hydrophosphination of the triple bond in enynes in the presence of yttriumcomplexes [247]. An ytterbium–imine complex 145 [Yb(η2-Ph2CNPh)(hmpa)3] has also been applied for the synthesis of alkenylphosphines [245][248][249][250][251]. The

Recent applications of the divinylcyclopropane–cycloheptadiene rearrangement in organic synthesis

• Sebastian Krüger and
• Tanja Gaich

Beilstein J. Org. Chem. 2014, 10, 163–193, doi:10.3762/bjoc.10.14

• , see Scheme 34) catalyzed by in situ formed W(CO)5(tol) upon irradiation to give annulated tricycle 275. The common mechanism for this type of reaction proceeds via endo-dig cyclization of enynes like 266 to give zwitterionic intermediate 267. Metal-carbenoid formation with subsequent cyclopropane

• 278) could be accessed. The selective formation of annulated bicycle 278 in preference of the possible bridged variant underlined the prefered reactivity of their enyne system. Gagosz and coworkers [211] recently showed that the cycloisomerization of enynes can be catalyzed by gold(I) catalysts. In a

• and Smith [219][220]. The synthesis of the cyclization precursors started from enynes like 297, beginning with cis-selective Rieke-Zn reduction. Epoxidation followed by oxidation furnished cis-vinylketone-epoxide 298. Enolate formation and acetate trapping afforded an intermediate enol-acetate, which

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

• 11d (R1 = H and R2 = Me) were converted to benzothiophenes 12c and 12d in 82% and 95% yield, respectively. The synthesis of substituted hydrindene 12e was also achieved in 85% yield from monosubstituted enyne 11e (R1 = Ph, R2 = H). Substituted enynes bearing heterocycles such as indole 11f (R1 and R2

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

• and co-workers demonstrated that 1,6-enynes like 24 when treated with appropriated gold complexes lead to related 1,4-zwitterionic homologs that can be efficiently intercepted by nitrones in a formal [4 + 3] cycloaddition reaction. The resulting 1,2-oxazepane derivatives 25 are isolated as single

Gold(I)-catalyzed 6-endo hydroxycyclization of 7-substituted-1,6-enynes

• Ana M. Sanjuán,
• Alberto Martínez,
• Patricia García-García,
• Manuel A. Fernández-Rodríguez and
• Roberto Sanz

Beilstein J. Org. Chem. 2013, 9, 2242–2249, doi:10.3762/bjoc.9.263

• )-3-(methylbut-2-enyl)benzenes, 1,6-enynes having a condensed aromatic ring at C3–C4 positions, has been studied under the catalysis of cationic gold(I) complexes. The selective 6-endo-dig mode of cyclization observed for the 7-substituted substrates in the presence of water or methanol giving rise to

• hydroxy(methoxy)-functionalized dihydronaphthalene derivatives is highly remarkable in the context of the observed reaction pathways for the cycloisomerizations of 1,6-enynes bearing a trisubstituted olefin. Keywords: catalysis; dihydronaphthalenes; gold; gold catalysis; hydroxycyclization; selectivity

• ; Introduction The cycloisomerization reactions of enynes catalyzed by gold complexes are a powerful tool for accessing complex products from rather simple starting materials under soft and straightforward conditions [1][2][3][4]. In this context, 1,6-enynes have been extensively studied, mainly by Echavarren

Gold(I)-catalyzed formation of furans from γ-acyloxyalkynyl ketones

• Marie Hoffmann,
• Solène Miaskiewicz,
• Jean-Marc Weibel,
• Patrick Pale and
• Aurélien Blanc

Beilstein J. Org. Chem. 2013, 9, 1774–1780, doi:10.3762/bjoc.9.206

• catalysts with their carbophilic character have emerged as a new tool for furan preparation. As summarized in Scheme 1, furans could now be obtained by either gold(I) or gold(III) catalysis from various types of substrates such as allenyl ketones [8][9][10][11][12][13][14], enynes or diynes [15][16][17

A reductive coupling strategy towards ripostatin A

• Kristin D. Schleicher and
• Timothy F. Jamison

Beilstein J. Org. Chem. 2013, 9, 1533–1550, doi:10.3762/bjoc.9.175

• laboratory [42][43], it is believed that epoxide oxidative addition precedes alkyne addition, as opposed to concerted oxidative coupling. At least when dimethylphenylphosphine is used as ligand, this may proceed via the intermediacy of a betaine species. In the reductive coupling reaction of enynes and

• epoxides, the olefin coordinates to nickel and directs alkyne insertion. Because of this directing effect, formation of the regioisomeric diene product is atypical for reductive coupling reactions of enynes and epoxides. However, in reactions of 1-phenyl-1-propyne and epoxides with oxygenation in the 3

• -dienes. Synthesis of cyclopropyl enyne. Synthesis of model epoxide for investigation of the nickel-catalyzed coupling reaction. Nickel-catalyzed enyne–epoxide reductive coupling reaction. Proposed mechanism for the nickel-catalyzed coupling reaction of alkynes or enynes with epoxides. Regioselectivity

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