Studies in Condensation Reactions

[摘要] The mechanism of the Thermal Michael reaction, i.e., the condensation of a Mannich base with a compound containing an activated methylene group, has been studied and evidence has been obtained which corroborates the postulated reaction steps. The Mannich bases of both phenyl acetylene and beta-naphthol have been prepared and their condensation with cyclohexanone attempted. The former compound fails to react, while a dihydropyran, the hemiketal of (1-[2'-oxocyclohexylmethyl])-(2-hydroxy)-naphthalene is isolated in 85% yield from the reaction of the latter compound. The structures of the isomeric diMannich bases of acetone, [1,5-bis(dimethylamino)]-pentan-3-one and (1-dimethylamino)-(2-dimethylaminomethyl)-butan-3-one, and of the diMannich base of methyl ethyl ketone, [1,5-bis-(dimethylamino)]-(4-methyl)-pentan-3-one, have been corroborated using N.M.R. evidence and the synthesis of bridged bicyclic ketones has been attempted by their condensation with cyclopentanone. This method was only successful in the case of the gem-diMannich base, (1-dimethylamino)-(2-dimethylaminomethyl)-butan-3-one. The condensation product,(3-acetyl)-bicyclo[3,2,1]-octan-8-one, was identified by its physical data and the results of deuteration studies. The two (1,5)-diMannich bases condensed with two molecules of cyclo-pentanone to give [1,5-bis(2'-oxocyclopentyl)]-pentan-3-ones. The use of a solvent, ethylene glycol, in the Thermal Michael reaction has also been investigated. Unless there is a particular need for such a condition, it was concluded that the use of excess ketone as solvent is advisable. The mass-spectral fragmentation patterns of a series of ethylene ketals of 2[beta-benzyl-ethyl ]-cyclopentanones have been examined to determine the positions of substitution in the cyclopentanone rings. This may be applied as a general method to determine the orientation of attack, which this work confirmed to take place invariably at the least substituted position.

[发布机构] University:University of Glasgow

[关键词] Organic chemistry