31247-59-3Relevant academic research and scientific papers
The Schmidt reaction of dialkyl acylphosphonates
Sprecher, Milon,Kost, Daniel
, p. 1016 - 1026 (2007/10/02)
The scope of the Schmidt rearrangement of ketones has been extended to dialkyl acylphosphonates (11a-11l). Surprisingly, it was found that 11a-11d and 11g, in which the acyl moiety was benzoyl alone or benzoyl bearing an electron-attracting or mildly electron-releasing substituent, yielded an overwhelming portion of products resulting from C-to-N migration of the aryl group (N-arylcarbamoylphosphonates, 12, and N-arylformamides, 15). Contrariwise, the arenecarbonylphosphonates, which carry a powerful electron-releasing p-alkoxy group, yielded products resulting from phosphonate group migration from C to N or elimination (dialkyl N-arenecarbonylphosphoramidates, 13, and arenecarbonitriles, 17, respectively). These counterintuitive results are rationalized by application of the concept of "degree of electron demand" to this area of intramolecular rearrangements. The possible existence of an additional pathway for the Schmidt rearrangement, involving protonation of the iminodiazonium ion, is proposed.
Vinyl Cation Intermediates in Solvolytic and Electrophilic Reactions. 1. Solvolysis of α-Arylvinyl Derivatives
Yates, Keith,Mandrapilias, George
, p. 3892 - 3902 (2007/10/02)
The solvolysis of 16 α-arylvinyl tosylates, bromides, and chlorides has been investigated in various alcohol-water mixtures and in acetic acid at several temperatures.All substrates were substituted with either 2-methyl or 2,6-dimethyl groups to accelerate the rates of reaction.The major or exclusive product isolated in most cases was the acetophenone arising from hydrolysis of the expected enol ethers or acetates during workup.The kinetics were simple first order in the vast majority of cases, with excess base added to prevent side reactions.Leaving group effects, Winstein-Grunwald m values, Schleyer Q values, and effects of solvent nucleophilicity all point to a limiting SN1 ionization generating a vinyl cation intermediate, in which there is little rear-side nucleophilic assistance by solvent.Substituent effects led to ρ values in the range -3.9 to -5.3 vs. ?+.Activation parameters are typical for an SN1 process, and ΔS% is insensitive to the presence of zero, one, or two o-methyl groups, as are the effects of solvent polarity on the rates.The results should therefore be directly comparable with other solvolytic or electrophilic reactions generating formally similar vinyl cation intermediates.
