From over-stoichiometric to sub-stoichiometric enantioselective protonation with 2-sulfinyl alcohols: A view in perspective
A general study of the enantioselective protonation of prochiral enolates with 2-sulfinyl alcohols is reported. The modification of reaction conditions to reduce drastically the amount of chiral proton source needed to obtain a good enantiomeric excess is reported. The effects of the different factors controlling the stereoselectivity are clearly established. Different protocols for enolate generation are compared. Medio Simon, Mercedes, Mercedes.Medio@uv.es ; Aleman Lopez, Pedro Antonio, Pedro.Aleman@uv.es ; Gil Tomas, Jesus Javier, Jesus.J.Gil@uv.es ; Asensio, Aguilar Gregorio, Gregorio.Asensio@uv.es
NHC-Stabilized Gold(I) Complexes: Suitable Catalysts for 6-exo-dig Heterocyclization of 1-(o-Ethynylaryl)ureas
3-Substituted 1-(o-ethynylaryl)ureas 1 selectively undergo either 6-exo-dig or 5-endo-dig cyclization (to give 4-methylene-3,4-quinazolin-2-ones 2 or indoles 3, respectively) depending on the choice of the metal, ligand, and reaction conditions. The best results (up to 96% yield) in the preparation of the hydroamination products 2 are achieved with the highly bulky NHC-stabilized cationic gold(I) complex [Au(IPr)](+). Conversely, ureas bearing an internal alkyne lead to the 5-endo-dig cyclization mode regardless of the gold(I) complex employed. Whereas the nature of the substituent at N-3 does not have any influence on the regiochemistry observed, it does, in some cases, affect the efficien…
Efficient synthesis of racemic and chiral alkenyl sulfoxides by palladium-catalyzed Suzuki coupling
Alkenyl sulfoxide derivatives are obtained in high yields through a palladium-catalyzed Suzuki/Miyaura cross-coupling reaction of racemic and chiral 1-halo sulfoxides with aryl and alkenyl boronic acids. Chiral substrates react with no loss of optical purity and high optical yields. The reaction takes place with different palladium catalysts, such as Pd(PPh 3 ) 4 or Pd(OAc) 2 /DABCO. Although nitrogen ligands like DABCO lead to an active palladium catalyst, they are less effective than the phosphine ones.
Gold(I)-Catalyzed Reactions of 1-(ortho-Alkynylaryl)ureas: Highly Selective Heterocyclization and Synthesis of MixedN,O-Acetals
Treatment of alkynylureas (I) with trifluoroethanol in the presence of a Au/Ag catalytic system provides N-6-exo-dig heterocyclization products (III) and in some cases open chain acetals as side products.
Osmium(III) Complexes with POP Pincer Ligands: Preparation from Commercially Available OsCl3·3H2O and Their X-ray Structures
Complexes OsCl3{dbf(PiPr2)2} [1; dbf(PiPr2)2 = 4,6-bis(diisopropylphosphino)dibenzofuran], OsCl3{xant(PiPr2)2} [2; xant(PiPr2)2 = 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene], and OsCl3{xant(PPh2)2} [3; xant(PPh2)2 = 9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene] have been obtained in high yield by the reaction of the corresponding diphosphine with OsCl3·3H2O. The ruthenium(III) counterparts RuCl3{dbf(PiPr2)2} (4), RuCl3{xant(PiPr2)2} (5), and RuCl3{xant(PPh2)2} (6) are similarly obtained from RuCl3·3H2O in moderate yields. The X-ray structures of dbf(PiPr2)2 and complexes 1−3 are also reported.
FeCl3·6H2O-catalyzed Mukaiyama-aldol type reactions of enolizable aldehydes and acetals.
Mukaiyama-aldol type reactions of acetals derived from enolizable aldehydes with FeCl3·6H2O, an eco-friendly, low-cost, and stable catalyst, lead to β-methoxycarbonyl compounds with nearly quantitative yields. The methodology is extended to the parent aldehydes as starting materials, leading to the corresponding aldols with lower yields, but efficiently. Different alkyl and aryl substituted acetals and aldehydes have been tested in the reaction with linear and cyclic silyl enol ethers. Reactions are carried out in an open air atmosphere, and additives are not required. Acetals can be considered activating groups of the carbonyl moiety rather than a protecting group in this type of FeCl3·6H2…
Water compatible gold(III)-catalysed synthesis of unsymmetrical ethers from alcohols.
An efficient and broad-scoped method for the preparation of unsymmetrical ethers from alcohols catalysed by the simplest and least expensive gold catalyst, NaAuCl 4 , is described for the first time. The procedure enables the etherification of benzylic and tertiary alcohols with moderate to good yields under mild conditions with low catalyst loading. Symmetrical ethers, the usual side products in the etherification of alcohols, were not detected in this case. The formation of the racemic ether from a chiral benzyl alcohol suggests the intermediacy of a carbocation, which has not previously been postulated for gold-catalysed reactions involving alcohols.