Synthesis of substituted enones
The palladium-catalyzed reaction of aryl bromides and iodides with acrolein diethyl acetal and subsequent hydrolysis by addition of 2 M HCl to the reaction mixture affords (E)-cinnamaldehydes in good yields. Various functional groups are tolerated.
G. Battistuzzi, S. Cacchi, G. Fabrizi, Org. Lett., 2003, 5, 777-780.
N-Vinylpyridinium and -trialkylammonium tetrafluoroborate salts represent a new class of electrophilic coupling partner for Pd(0)-catalyzed Suzuki cross-coupling reactions with various boronic acids in high yields. The crystalline, air-stable, and nonhygroscopic salts are easily prepared from activated acetylenes and pyridinium or trialkylammonium tetrafluoroborates.
K. R. Buszek, N. Brown, Org. Lett., 2007, 9, 707-710.
A Pd-catalyzed oxidative cross-coupling reaction of arylboronic acids with α-diazoesters using molecular oxygen as the reoxidant gives E-α,β-diarylacrylates in good yields and very high E-to-Z selectivity.
Y.-T. Tsoi, Z. Zhou, A. S. C. Chan, W.-Y. Yu, Org. Lett., 2010, 12, 4506-4509.
Conjugate addition of organozinc reagents to readily available 2,3-allenals enables a unique and practical method for the preparation of stereodefined, fully substituted olefins bearing an extremely versatile aldehyde functionality. The geometry of the newly formed double bond is controlled by unique regiospecific oxygen-protonation of the enolate intermediates, generating 1,3-alkadienols, followed by 1,5-H-transfer.
J. Dai, N. Wang, G. Chai, C. Fu, S. Ma, J. Am. Chem. Soc., 2016, 138, 2532-2535.
A mild and practically-convenient one-pot procedure for the direct β-substitution of enones has been developed using a conjugate addition-oxidation strategy with a full range of copper-based reagents (R2CuLi, RCu.SMe, RCu, R(2-thienyl)Cu(CN)Li2) and N-tert-butylphenylsulfinimidoyl chloride. Cyclic and acyclic, alkyl- and aryl-substituted enones are delivered in good to excellent yields.
W. J. Kerr, C. M. Person, G. J. Thurston, Org. Biomol. Chem., 2006, 4, 47-50.
Silyloxyallenes serve as highly useful α-acylvinyl anion equivalents, that undergo conjugate additions to alkylidene malonates in the presence of Sc(OTf)3 as catalyst. The reaction delivers intermolecular Rauhut-Currier products in excellent yields and regioselectivities for a wide scope of substrates.
T. E. Reynolds, M. S. Binkley, K. A. Scheidt, Org. Lett., 2008, 10, 2449-2452.
Silylated cyanohydrins of iodo-substituted aryl, heteroaryl, or cycloalkenyl ketones undergo an I/Mg-exchange using i-PrMgCl·LiCl. After subsequent reactions with electrophiles, a facile deprotection produces polyfunctional ketones in good overall yiels. An extension to aromatic iodoaldehydes is described.
C.-Y. Liu, H. Ren, P. Knochel, Org. Lett., 2006, 8, 617-629.
A bifunctional organocatalyst enables a 1,3-addition of silyl-dienol ethers to nitroalkenes to provide Rauhut-Currier type products with tri- and tetrasubstituted double bonds. The process takes place under smooth, nonanionic conditions, and with high enantiomeric excess. A rational mechanistic pathway is presented based on DFT and mechanistic experiments.
M. Frias, R. Mas-Ballesté, S. Arias, C. Alvarado, J. Alemán, J. Am. Chem. Soc., 2017, 139, 672-679.
An organocatalytic highly enantioselective formation of vinyl-substituted all-carbon quaternary stereocenters proceeds in good yield via nucleophilic vinylic substitution of various α-substituted-α-cyanoacetates with α-chloroalkenones using a dimeric cinchona alkaloid phase-transfer catalyst.
M. Bell, T. B. Poulsen, K. A. Jørgensen, J. Org. Chem., 2007, 72, 3053-3056.
An entrapped Rh catalyst derived by a sol-gel process, has been used in a Pauson-Khand reaction under mild conditions. The catalyst can be reused at least 10 times without losing activity. This catalytic system is not effective for intermolecular reactions.
K. H. Park, S. U. Song, Y. K. Chung, Tetrahedron Letters, 2003, 44, 2827-2830.
The Rh(I)-catalyzed [3 + 2] cycloaddition of cyclopropenones and alkynes provides a highly efficient and regioselective route to cyclopentadienones (CPDs) that would be otherwise difficult to obtain. The versatility of the method is explored with a wide range of alkynes and diaryl- as well as arylalkylcyclopropenones.
P. A. Wender, T. J. Paxton, T. J. Williams, J. Am. Chem. Soc., 2006, 128, 14814-14815.
Various arylallenes and alkenylallenes were prepared via coupling of allenylstannanes with aryl iodides or alkenyl iodides in the presence of Pd(PPh3)4 as catalyst, LiCl, and DMF as solvent.
C.-W. Huang, M. Shanmugasundaram, H.-M. Chang, C.-H. Cheng, Tetrahedron, 2003, 59, 3635-3641.
|Copper-Catalyzed Conjugate Addition to α,β-Unsaturated Carbonyl Compounds|