Synthesis of substituted 1,3-enynes
The cross-coupling reaction of (E)- and (Z)-alk-1-enyldialkylborane with (trimethylsilyl)ethynyl bromide proceeds in the presence of a catalytic amount of copper(II) acetylacetonate and a base under extremely mild conditions to provide conjugated enynes with a distal carbon-carbon triple bond.
M. Hoshi, N. Kawamura, K. Shirakawa, Synthesis, 2006, 1961-1970.
Cross-coupling of 1-alkynes with vinyl iodides catalyzed by CuI/N,N-dimethylglycine affords conjugated enynes in good to excellent yields. Heating a mixture of 2-bromotrifluoroacetanilide, 1-alkyne in the presence of CuI/L-proline leads to the formation of the corresponding indole.
F. Liu, D. Ma, J. Org. Chem., 2007, 72, 4844-4850.
A palladium(II) complex based on N,N-dimethylethanolamine can be used as a catalyst in copper-free Sonogashira couplings of (E)- or (Z)-bromostyrenes with alkynes to produce conjugated enynes at room temperature in good yields with retention of the configuration.
X. Mi, M. Huang, Y. Feng, Y. Wu, Synlett, 2012, 1257-1261.
A copper(I)-catalyzed coupling of alkynes with vinyl iodides affords various enynes in good to excellent yields, tolerates a variety of functional groups, and does not require the use of expensive additives.
C. G. Bates, P. Saejueng, D. Venkataraman, Org. Lett., 2004, 6, 1441-1444.
Multifunctional palladium catalysis allows a one-pot stereocontrolled synthesis of tetrasubstituted methyl ketones and enynes. The homogeneous palladium dihalide catalyst is used for the bromo-/chloroallylation of alkynes and in situ for subsequent Wacker-Tsuji oxidation or Sonogashira cross-coupling.
A. N. Thadani, V. H. Rawal, Org. Lett., 2002, 4, 4321-4323.
Alkynyl Grignard reagents, prepared from the corresponding alkynes and methylmagnesium bromide, react with alkenyl bromides or triflates in the presence of FeCl3 as catalyst and lithium bromide as additive to give the corresponding conjugated enynes in high to excellent yields. The reaction shows wide applicability to various terminal alkynes and alkenyl electrophiles.
T. Hatakeyama, Y. Yoshimoto, T. Gabriel, M. Nakamura, Org. Lett., 2008, 10, 5341-5344.
A simple procedure for the synthesis of substituted (E)-2-alkene-4-ynecarboxylic esters has been achieved using hydroxyapatite-supported palladium as efficient catalyst surface. The highly efficient catalyst can be recycled.
B. C. Ranu, L. Adak, K. Chattopadhyay, J. Org. Chem., 2008, 73, 5609-5612.
An efficient, palladium-catalyzed synthesis of 2-alkene-4-ynoates and -nitriles by a simple reaction of vic-diiodo-(E)-alkenes with acrylic esters and nitriles in water leads to (E)-isomers from acrylic esters exclusively, whereas (Z)-isomers are obtained in high stereoselectivity from reactions of acrylonitrile. The in situ prepared Pd(0) nanoparticles can be recycled.
B. C. Ranu, K. Chattopadhyay, Org. Lett., 2007, 9, 2409-2412.
A straightforward one-pot approach to highly diverse conjugated enynes, starting from carbonyl precursors has been developed. The low nucleophilic phosphazene bases, which are used for the generation of the alkenyl nonaflates and the terminal alkynes, are compatible with NfF and do not impede the subsequent Sonogashira reaction.
I. M. Lyapkalo, M. A. K. Vogel, Angew. Chem. Int. Ed., 2006, 45, 4019-4023.
An efficient synthesis of structurally diverse fused furans in good yields from 2-alkynylcycloalk-2-enols via gold(III) bromide catalyzed cycloisomerization was achieved under moderate reaction conditions.
C. Praveen, P. Kiruthiga, P. T. Perumal, Synlett, 2009, 1990-1996.
2-Alkynyl esters are stereo- and regioselectively converted to E-β-chloro-α-iodo-α,β-unsaturated esters by exposure to Bu4NI in refluxing dichloroethane. Single-isomer tetrasubstituted olefins bearing four different carbon substituents are then synthesized by sequential palladium-catalyzed coupling reactions.
A. B. Lemay, K. S. Vulic, W. W. Ogilvie, J. Org. Chem., 2006, 71, 3615-3618.
Dinuclear and mononuclear palladium complexes with N,N'-bis[2-(diphenylphosphino)phenyl]amidinate (DPFAM) as a ligand catalyzed the cross-addition of triisopropylsilylacetylene (TIPSA) to unactivated internal alkynes, giving enynes selectively. The reactions of TIPSA with several terminal alkynes also gave cross-adducts selectively, although the yields were moderate.
N. Tsukada, S. Ninomiya, Y. Aoyama, Y. Inoue, Org. Lett., 2007, 9, 2919-2921.
Alkynylboration of alkynes with alkynyl(pinacol)boranes in the presence of nickel catalysts gave cis-1-borylbut-1-en-3-yne derivatives. Some boryl-substituted enynes were reacted with sp2 halides under Suzuki-Miyaura coupling conditions.
M. Suginome, M. Shirakura, A. Yamamoto, J. Am. Chem. Soc., 2006, 128, 14438-14439.