133658-79-4Relevant academic research and scientific papers
Cyclopropylketenes: preparation and nucleophilic additions
Allen, Annette D.,Baigrie, Lynn M.,Gong, Leyi,Tidwell, Thomas T.
, p. 138 - 145 (2007/10/02)
Phenylcyclopropylketene (4), tert-butylcyclopropylketene (5), and dicyclopropylketene (6) were formed by dehydrochlorination of the corresponding acyl chlorides by Et3N in THF, and are the first cyclopropylketenes to be isolated and purified.Reaction of 4 with n-BuLi and capture of the intermediate enolates with Me3SiCl gave the stereoisomeric silyl enol ethers c-PrCPh=C(OSiMe3)-n-Bu with a 79:21 preference for formation of the Z isomer resulting from nucleophilic attack syn to cyclopropyl, whereas the corresponding reaction of t-BuLi gave 9:91 preference for attackanti to cyclopropyl.Some isopropyl-, cyclopentyl-, and cyclohexylketenes gave comparable results.Analyses of the relative sizes of the ketene substituents in the ground state by steric parameters, and of the product stabilities by molecular mechanics, both fail to predict the observed similarities in the results with different secondary alkyl groups.The hydration reactivities of 4 and 6 show that, in neutral H2O/CH3CN, c-PrCPh=C=O is more reactive than i-PrCPh=C=O, a result ascribed as mainly due to the smaller size of cyclopropyl. c-Pr2C=C=O has the same reactivity in neutral water as Et2C=C=O, but is 22 times less reactive with acid, a result attributed to the inability of the β-cyclopropyl groups to directly stabilize the cationic transition state for protonation. Key words: cyclopropylketenes, ketenes, nucleophilic addition, hydration kinetics.
Ring and C-O Bond Fragmentation as Tools for Fingerprinting the Extent of Homolysis during Base-Catalyzed Carbon-Carbon Bond Cleavages of the Haller-Bauer, Cram, and Gilday Types
Paquette, Leo A.,Maynard, George D.
, p. 5054 - 5063 (2007/10/02)
The mechanisms of the base-catalyzed cleavage of non-enolizable ketones (Haller-Bauer reaction), fragmentation of the alkali-metal salts of diphenylcarbinols (Cram cleavage), and decarboxylative elimination of methyllithium-carboxylic acid adducts (Gilday process) are probed by attaching a small ring or a carbon-oxygen bond proximal to the ultimate seat of reaction.Particular attention is given to whether product formation in the first case is accompanied by fission of the cyclopropane or cyclobutane subunit.The product distributions constitute a serviceable diagnostic of the relative extent to which carbanion and radical pathways operate concurrently.This distinction is also possible in the oxa analogues since the homolysis/heterolysis dichtomy is matched by retention of an intact C-O bond and the extent of its cleavage, respectively.A key feature of the Haller-Bauer process is its ability to deliver debenzoylated products having intact cyclopropane or cyclobutane rings because of its strong predilection for the generation of carbanions during C-C bond fragmentation.Counterion influences are minimal.The Cram cleavages show a very different product distribution profile.The results can be plausibly fitted to the involvement of free radicals, although the distinction between direct C-C bond hemolysis or heterolysis followed by rapid black-electron transfer cannot be made at this time.Because the Gilday reaction leads directly to styrenes and these products suffer destruction under the reaction conditions, this transformation lacks synthetic value in this particular context.
