- An Amine-Assisted Ionic Monohydride Mechanism Enables Selective Alkyne cis-Semihydrogenation with Ethanol: From Elementary Steps to Catalysis
-
The selective synthesis of Z-alkenes in alkyne semihydrogenation relies on the reactivity difference of the catalysts toward the starting materials and the products. Here we report Z-selective semihydrogenation of alkynes with ethanol via a coordination-induced ionic monohydride mechanism. The EtOH-coordination-driven Cl- dissociation in a pincer Ir(III) hydridochloride complex (NCP)IrHCl (1) forms a cationic monohydride, [(NCP)IrH(EtOH)]+Cl-, that reacts selectively with alkynes over the corresponding Z-alkenes, thereby overcoming competing thermodynamically dominant alkene Z-E isomerization and overreduction. The challenge for establishing a catalytic cycle, however, lies in the alcoholysis step; the reaction of the alkyne insertion product (NCP)IrCl(vinyl) with EtOH does occur, but very slowly. Surprisingly, the alcoholysis does not proceed via direct protonolysis of the Ir-C(vinyl) bond. Instead, mechanistic data are consistent with an anion-involved alcoholysis pathway involving ionization of (NCP)IrCl(vinyl) via EtOH-for-Cl substitution and reversible protonation of Cl- ion with an Ir(III)-bound EtOH, followed by β-H elimination of the ethoxy ligand and C(vinyl)-H reductive elimination. The use of an amine is key to the monohydride mechanism by promoting the alcoholysis. The 1-amine-EtOH catalytic system exhibits an unprecedented level of substrate scope, generality, and compatibility, as demonstrated by Z-selective reduction of all alkyne classes, including challenging enynes and complex polyfunctionalized molecules. Comparison with a cationic monohydride complex bearing a noncoordinating BArF- ion elucidates the beneficial role of the Cl- ion in controlling the stereoselectivity, and comparison between 1-amine-EtOH and 1-NaOtBu-EtOH underscores the fact that this base variable, albeit in catalytic amounts, leads to different mechanisms and consequently different stereoselectivity.
- Huang, Zhidao,Wang, Yulei,Leng, Xuebing,Huang, Zheng
-
supporting information
p. 4824 - 4836
(2021/04/07)
-
- A highly tunable stereoselective olefination of semistabilized triphenylphosphonium ylides with N -Sulfonyl imines
-
The Wittig reaction involving direct olefination of triphenylphosphonium ylides (Ph3PCHR) with aldehydes is arguably the most often used method for alkene synthesis, but in general it yields mixtures of Z- and E-alkenes for semistabilized triphenylphosphonium ylides (R = aryl or vinyl). We have developed a simple and efficient protocol to improve the stereoselectivity significantly by replacing the aldehydes used in the Wittig reaction with N-sulfonyl imines, which possess distinct electronic and steric properties relative to aldehydes. A broad range of aromatic, α,β-unsaturated, and aliphatic imines bearing appropriate N-sulfonyl groups smoothly undergo olefination reaction 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. Moreover, this tunable protocol has been successfully applied to the highly stereoselective synthesis of two anticancer agents, DMU-212 and its Z-isomer.
- Dong, De-Jun,Li, Hai-Hua,Tian, Shi-Kai
-
supporting information; experimental part
p. 5018 - 5020
(2010/06/13)
-
- 1,2- vs 1,4-Addition of acylbenzotriazoles to α,β-unsaturated aldehydes and ketones. A novel route to 3-alkyl-4,6-diaryl-3,4-dihydropyran-2-ones
-
Lithiation of aliphatic 1-acylbenzotriazoles with subsequent reaction with α,β-unsaturated ketones and aldehydes affords either 3,4,6-trisubstituted 3,4-dihydropyran-2-ones or 1,3-dienes depending on the carbonyl reagent used. Substituent effects on product yield and isomer ratio are discussed.
- Katritzky, Alan R.,Denisko, Olga V.
-
p. 3104 - 3108
(2007/10/03)
-
- Ruthenium-catalyzed coupling of unactivated olefins with unactivated alkynes
-
A new ruthenium-catalyzed coupling reaction of an olefin with an alkyne is presented. The C-H bond of the olefin formally undergoes trans addition to the C-C triple bond to produce conjugated dienes.
- Murakami, Masahiro,Ubukata, Minoru,Ito, Yoshihiko
-
p. 7361 - 7364
(2007/10/03)
-
- Palladium-catalysed Arylation of 1,3-Dienes: A Highly Chemo, Regio and Stereoselective Synthesis of (E,E) Conjugated Dienic Aromatics.
-
(E,E) conjugated aromatic dienes can be efficiently prepared from aromatic halides and 1,3-dienes with high chemo, regio and stereoselectivities. Key words: Palladium; arylation; dienes; silver(I) salt; thallium(I) salt; (E,E) conjugated dienic aromatics.
- Jeffery, Tuyet
-
p. 1989 - 1992
(2007/10/02)
-