24264-08-2Relevant academic research and scientific papers
Enantioselective staudinger synthesis of β-lactams catalyzed by a planar-chiral nucleophile
Hodous, Brian L.,Fu, Gregory C.
, p. 1578 - 1579 (2002)
The development of efficient methods for the stereoselective generation of β-lactams is an important goal, due to their biological activity and their utility as synthetic intermediates. The Staudinger reaction, an overall [2 + 2] cycloaddition of a ketene
Lewis acid-promoted ketene-alkene [2 + 2] cycloadditions
Rasik, Christopher M.,Brown, M. Kevin
supporting information, p. 1673 - 1676 (2013/04/10)
Described are the first examples of ketene-alkene [2 + 2] cycloadditions promoted by Lewis acids. Notable features of this method include (1) substantial rate acceleration relative to traditional thermal reactions, (2) good diastereoselectivities and yields for the formation of the cyclobutanone products, and (3) inverse diastereoselectivity compared with related thermal cycloadditions for many examples. These studies not only provide access to synthetically versatile cyclobutanones that cannot be prepared by traditional thermal cycloadditions but also address important mechanistic questions regarding ketene-alkene [2 + 2] cycloaddition reactions.
Asymmetric synthesis of highly substituted β-lactones by nucleophile-catalyzed [2+2] cycloadditions of disubstituted ketenes with aldehydes
Wilson, Jonathan E.,Fu, Gregory C.
, p. 6358 - 6360 (2007/10/03)
α,α-Disubstituted β-lactones can be obtained by the cycloaddition of the corresponding ketenes with aldehydes (see scheme). For the first time, a chiral PPY derivative, 1, serves as an efficient catalyst for the asymmetric synthesis of β-lactones (PPY = 4-pyrrolidin-1-ylpyridine). To date, this is the only catalyst that is effective for enantioselective cycloadditions of disubstituted ketenes with aldehydes. (Chemical equation presented).
Kinetics and Mechanism of Hydration of Alkylketenes
Allen, Annette D.,Tidwell, Thomas T.
, p. 2774 - 2780 (2007/10/02)
The hydration reactivities of CH2=C=O (1), t-Bu2C=C=O (5), Et2C=C=O (7), (CH2)4C=C=O (8), (CH2)5C=C=O (9), and t-BuCH=C=O (10) in H2O or H2O/CH3CN mixtures have been examined, including acid and base catalysis and solvent and structural isotope effects.These results provide the first systematic comparison of structural effects on the hydration of aliphatic ketenes, as well as the first measurements of base-induced hydration and pH-rate profiles for this process.The significant steric and electronic effects of the substituents observed lead to the interpretation that the acid-catalyzed reaction involves rate-limiting proton transfer to Cβ perpendicular to the ketene plane, while the H2O- and OH--induced reactions involve nucleophilic attack in the ketene plane.These results resolve the many conflicting previous reports and interpretations regarding ketene hydration.
Generation, Alkylation, and Silylation of Directed Enolates Formed by Reaction of Ketenes and Organolithium Reagents
Baigrie, Lynn M.,Lenoir, Dieter,Seikaly, Hani R.,Tidwell, Thomas T.
, p. 2105 - 2109 (2007/10/02)
Symmetrical ketenes R2C=C=O R2=t-Bu2(1), Et2(2),(CH2)4(3),(CH2)5(4) were reacted with organolithium reagents R'Li to give directed enolates R2C=C(OLi)R' which were alkylated with MeI or silylated with Me3SiCl.The silylation results for 2-4 were compared to those for reaction of ketones R2CHCO-n-Bu (16-18) with Me3SiCl and either i-Pr2NLi, KH, or Et3N.These latter conditions usually favored different regioisomers from the ketene route.Reaction of 1 with t-BuLi gave the previously inaccessible enolate t-Bu2C=C(OLi)-t-Bu (25), which on reaction with MeI gave a mixtureof the O-methylation product 27 along with some C-methylation product and with Me3SiCl gave the silyl enol ether 26.The vinyl ethers 26 and 27 are among the first substituted tri-tert-butylethylenes which have been reported.
