Categories: C=C Bond Formation >
Synthesis of (Z)-alkenes
N-sulfonyl imines undergo olefination reactions with various benzylidenetriphenylphosphoranes or allylidenetriphenylphosphoranes under mild reaction conditions to afford an array of both Z- and E-isomers of conjugated alkenes in good to excellent yields and with greater than 99:1 stereoselectivity depending on the N-sulfonyl group.
D.-J. Dong, H.-H. Li, S.-K. Tian, J. Am. Chem. Soc., 2010, 132, 5018-5020.
Deprotonation of 3,3,3-trichloropropyl-1-triphenylphosphonium chloride generates the corresponding phosphorane, which reacts with aldehydes to give trichloromethylated (Z)-olefins, which are useful for the synthesis of (Z)-1,3-enynes, (Z,Z)-1-chloro-1,3-dienes, and 1,3-diynes in high yields and stereospecificities.
M. S. Karatholuvhu, P. L. Fuchs, J. Am. Chem. Soc., 2004, 126, 14314-14315.
Fe(0) is cost-effective, environmentally friendly alternative to Cr(II) for the olefination of carbonyls by activated polyhalides. Fe(0) proved compatible with a wide range of functionality, such as unprotected phenol, aryl nitro, carboxylic acid, and alkyl nitrile.
J. R. Falck, R. Bejot, D. K. Barma, A. Bandyopadhyay, S. Joseph, C. Mioskowski, J. Org. Chem., 2006, 71, 8178-8182.
Peterson reagents, in which alkyloxy groups on the silicon atom fix the conformation of the anion after treatment with Li-base, were reacted with a variety of aldehydes to give Z-α,β-unsaturated sulfones with high Z-selectivity in very good yields. For the reaction with aliphatic aldehydes, cyclopentyl methyl ether is the solvent of choice, while 1,2-dimethoxyethane gave higher selectivity for the reaction with aromatic aldehydes.
K. Ando, T. Wada, M. Okumura, H. Sumida, Org. Lett., 2015, 17, 6026-6029.
Catalytic access to thermodynamically less stable Z-alkenes have relied upon kinetic control of the reaction. A mild and simple orthogonal approach proceeds via photochemically catalyzed isomerization of the thermodynamic E-alkene to the less stable Z-isomer via a photochemical pumping mechanism.
K. Singh, S. J. Staig, J. D. Weaver, J. Am. Chem. Soc., 2014, 136, 5275-5278.