19980-35-9Relevant articles and documents
Enolate-Based Regioselective Anti-Beckmann C-C Bond Cleavage of Ketones
Jahn, Ullrich,Ma?ek, Tomá?
, p. 11608 - 11632 (2021/09/02)
The Baeyer-Villiger or Beckmann rearrangements are established methods for the cleavage of ketone derivatives under acidic conditions, proceeding for unsymmetrical precursors selectively at the more substituted site. However, the fragmentation regioselectivity cannot be switched and fragmentation at the less-substituted terminus is so far not possible. We report here that the reaction of ketone enolates with commercial alkyl nitrites provides a direct and regioselective way of fragmenting ketones into esters and oximes or ω-hydroxyimino esters, respectively. A comprehensive study of the scope of this reaction with respect to ketone classes and alkyl nitrites is presented. Control over the site of cleavage is gained through regioselective enolate formation by various bases. Oxidation of kinetic enolates of unsymmetrical ketones leads to the otherwise unavailable "anti-Beckmann"cleavage at the less-substituted side chain, while cleavage of thermodynamic enolates of the same ketones represents an alternative to the Baeyer-Villiger oxidation or the Beckmann rearrangement under basic conditions. The method is suited for the transformation of natural products and enables access to orthogonally reactive dicarbonyl compounds.
Facile isomerization of silyl enol ethers catalyzed by triflic imide and its application to one-pot isomerization-(2 + 2) cycloaddition
Inanaga, Kazato,Ogawa, Yu,Nagamoto, Yuuki,Daigaku, Akihiro,Tokuyama, Hidetoshi,Takemoto, Yoshiji,Takasu, Kiyosei
supporting information; experimental part, p. 658 - 661 (2012/06/01)
A triflic imide (Tf2NH) catalyzed isomerization of kinetically favourable silyl enol ethers into thermodynamically stable ones was developed. We also demonstrated a one-pot catalytic reaction consisting of (2 + 2) cycloaddition and isomerization. In the reaction sequence, Tf2NH catalyzes both of the reactions.
Enantioselective decarboxylative alkylation reactions: Catalyst development, substrate scope, and mechanistic studies
Behenna, Douglas C.,Mohr, Justin T.,Sherden, Nathaniel H.,Marinescu, Smaranda C.,Harned, Andrew M.,Tani, Kousuke,Seto, Masaki,Ma, Sandy,Novak, Zoltan,Krout, Michael R.,McFadden, Ryan M.,Roizen, Jennifer L.,Enquist Jr., John A.,White, David E.,Levine, Samantha R.,Petrova, Krastina V.,Iwashita, Akihiko,Virgil, Scott C.,Stoltz, Brian M.
supporting information; experimental part, p. 14199 - 14223 (2012/02/01)
α-Quaternary ketones are accessed through novel enantioselective alkylations of allyl and propargyl electrophiles by unstabilized prochiral enolate nucleophiles in the presence of palladium complexes with various phosphinooxazoline (PHOX) ligands. Excellent yields and high enantiomeric excesses are obtained from three classes of enolate precursor: enol carbonates, enol silanes, and racemic β-ketoesters. Each of these substrate classes functions with nearly identical efficiency in terms of yield and enantioselectivity. Catalyst discovery and development, the optimization of reaction conditions, the exploration of reaction scope, and applications in target-directed synthesis are reported. Experimental observations suggest that these alkylation reactions occur through an unusual inner-sphere mechanism involving binding of the prochiral enolate nucleophile directly to the palladium center. Sly as a PHOX: The development of an enantioselective decarboxylative palladium-catalyzed allylic alkylation reaction, utilizing phosphinooxazoline ligands, is described. The catalyst is applied to a range of allyl enol carbonate, silyl enol ether, and allyl β-ketoester substrates to provide alkylated ketone products in excellent yield and good ee (see scheme). The utility of these products is demonstrated by their use in several asymmetric syntheses. Mechanistic studies are reported suggesting an unusual inner-sphere mechanism. Copyright
