Synthesis of α,β-unsaturated compounds
A copper(I)-catalyzed carboxylation reaction of aryl- and alkenylboronic esters under CO2 showed wide generality with higher functional group tolerance compared to the corresponding Rh(I)-catalyzed reaction.
J. Takaya, K. Ukai, N. Iwasawa, Org. Lett., 2008, 10, 2697-2700.
Treatment of 2,2-dimethylpropan-1,3-diol esters of aryl- and alkenylboronic acids with a catalytic amount of [Rh(OH)(cod)]2 in the presence of 1,3-bis(diphenylphosphino)propane and CsF in dioxane at 60°C under carbon dioxide atmosphere gave carboxylic acids in good yields.
K. Ukai, M. Aoki, J. Takaya, N. Iwasawa, J. Am. Chem. Soc., 2006, 128, 8706-8707.
A Cs2CO3-promoted carboxylation of N-tosylhydrazones and CO2 proceeded efficiently at 80°C under atmospheric CO2 and gave the corresponding α-arylacrylic acids in good yields.
S. Sun, J.-T. Yu, Y. Jiang, J. Cheng, J. Org. Chem., 2015, 80, 2855-2860.
Cp2TiCl2-catalyzed exchange of alkenes with Grignard reagents and subsequent reaction with CO2 provides carboxylic acids in high yields. The reaction proceeds with a wide range of alkenes under mild conditions. Styrenes can be transformed to α-aryl carboxylic acids, and aliphatic alkenes give linear alkanoic acids.
P. Shao, S. Wang, C. Chen, C. Xi, Org. Lett., 2016, 18, 2050-2053.
A mild and user-friendly Ni-catalyzed regioselective hydrocarboxylation enables a regioselective conversion of a broad range of alkynes with CO2 (1 bar) while obviating the need for sensitive organometallic species and using simple alcohols as proton sources.
X. Wang, M. Nakajima, R. Martin, J. Am. Chem. Soc., 2015, 137, 8924-8927.
Various alkenylzirconocenes, prepared in situ by a carbozirconation of alkynes, were efficiently carboxylated in the presence of CO2 using (IMes)CuCl as catalyst at room temperature to provide the corresponding α,β-unsaturated carboxylic acids in good yields.
S. Wang, P. Shao, C. Chen, C. Xi, Org. Lett., 2015, 17, 5112-5115.
An enantioselective alkoxycarbonylation-amination cascade process of terminal allenes with CO, methanol, and arylamines proceeds under mild conditions (r.t., ambient pressure CO) via oxidative Pd(II) catalysis using a chiral aromatic spiroketal-based diphosphine ligand and a Cu(II) salt as an oxidant to afford various α-methylene-β-arylamino acid esters in good yields with excellent enantioselectivity and high regioselectivity.
J. Liu, Z. Han, X. Wang, Z. Wang, K. Ding, J. Am. Chem. Soc., 2015, 137, 15346-15349.
The use of Mo(CO)6 and an amine enables a regiospecific, Pd-free aminocarbonylation of various terminal alkynes. The Mo(CO)6-amine system played a dual role as complexing agent and as CO donor.
A. Nagarsenkar, S. K. Prajapti, S. D. Guggilapu, B. N. Babu, Org. Lett., 2015, 17, 4592-4595.
Formamides undergo addition reactions across alkynes and 1,3-dienes by nickel/Lewis acid catalysis to give stereo- and regioselectively various α,β- and β,γ-unsaturated amides. The presence of Lewis acid cocatalysts is crucial, and formamide coordination to the Lewis acid is considered to be responsible for the activation of their formyl C-H bonds probably through oxidative addition to nickel(0).
Y. Nakao, H. Idei, K. S. Kanyiva, T. Hiyama, J. Am. Chem. Soc., 2009, 131, 5070-5071.
A palladium-catalyzed cross-coupling reaction between organoboronic acids and commercially available N-methoxy-N-methylcarbamoyl chloride allows the synthesis of Weinreb benzamides and heteroaromatic analogues, as well as α,β-unsaturated Weinreb amides. This simple protocol is also applicable to the use of potassium organotrifluoroborates.
R. Krishnamoorthy, S. Q. Lam, C. M. Manley, R. J. Herr, J. Org. Chem., 2010, 75, 1251-1258.
A convenient approach to selectively prepare a wide range of functionalized propiolic acids was developed by AgI-catalyzed carboxylation of terminal alkynes using carbon dioxide as carboxylative agent under ligand-free conditions.
X. Zhang, W.-Z. Zhang, X. Ren, L.-L. Zhang, X.-B. Lu, Org. Lett., 2011, 13, 2402-2405.
A simple, chemoselective Ni-catalyzed reductive cyclization/carboxylation of unactivated alkyl halides with CO2 operates under mild conditions.
X. Wang, Y. Liu, R. Martin, J. Am. Chem. Soc., 2015, 137, 6476-6479.
A nickel-catalyzed double carboxylation of internal alkynes proceeds under CO2 (1 atm) at room temperature in the presence of a nickel catalyst, Zn powder as a reducing reagent, and MgBr2 as an indispensable additive. Various internal alkynes could be converted to the corresponding maleic anhydrides in good to high yields.
T. Fujihara, Y. Horimoto, T. Mizoe, F. B. Sayyed, Y. Tani, J. Terao, S. Sakaki, S. Tsuji, Org. Lett., 2014, 16, 4960-4963.
The combination of [(π-allyl)PdCl]2 with [(R)-ECNU-Phos], a new chiral bisphosphine ligand based on a biphenyl skeleton, demonstrates high enantioselectivity in a catalytic asymmetric carbonylation of readily available racemic propargylic carbonates to access optically active 2,3-allenoates.
Y. Wang, W. Zhang, S. Ma, J. Am. Chem. Soc., 2013, 135, 11517-11520.
Palladium-catalyzed alkoxycarbonylation of 2,4-enyne carbonates proceeds in an alcohol and under balloon pressure of CO through 1,5-substitution. The olefin geometry controls the overall stereochemistry of this alkoxycarbonylation method.
E. Ş. Karagöz, M. Kuş, G. E. Akpınar, L. Artok, J. Org. Chem., 2014, 79, 9222-9230.
Pd(0)-catalyzed carbonylation of (Z)-2-en-4-yn carbonates in the presence of CO and an alcohol gives vinylallenyl esters with an exclusively E-configuration in high yields. The unreactivity of E-configured enyne carbonates may indicate that the reaction is promoted via the cooperative coordination of palladium with both alkynyl and carbonate moieties.
G. E. Akpınar, M. Kuş, M. Uçncu, E. Karakuş, L. Artok, Org. Lett., 2011, 13, 748-751.