94368-07-7Relevant academic research and scientific papers
Stereoselectivity of the Transfer of Hydrogen Atoms to Cyclic Alkyl Radicals
Metzger, Juergen O.,Schwarzkopf, Kay,Saak, Wolfgang,Pohl, Siegfried
, p. 1069 - 1074 (2007/10/02)
The addition of cyclohexane to alkylmaleic anhydrides 1a-f via cyclic radicals 2a-f gave a mixture of (Z)- and (E)-2,3-dialkylsuccinic anhydrides 3a-f.The stereoselectivity of the hydrogen transfer from cyclohexane to radicals 2a-d was measured in the temperature range of 200-260 deg C, and the relative activation parameters of the formation of (Z)- and (E)-3 were determined.The stereoselectivity of the hydrogen transfer from cyclohexylmercuric hydride at 25 deg C was measured as well.The results are rationalized assuming steric interactions in the transition state of H donor and β substituent and of α and β substituent, respectively.An X-ray structure analysis of the highly strained addition product (Z)-3d was performed. - Key Words: Free-radical additions / Alkyl radicals / Stereoselectivity / Hydrogen transfer
Radical Chain Reactions with Maleic Anhydrides - Contrathermodynamic Stereoselectivity
Giese, Bernd,Kretzschmar, Gerhard
, p. 3175 - 3182 (2007/10/02)
The reactions of cyclohexylmercuric chloride with NaBH4 and alkenes 1a-g yield 60-84percent of products 3, 4 and 6 in a radical chain process (table 1).Caused by steric effects of substituents Z at least 97percent of the radical attack occurs at the unsubstituted carbon atom of maleic anhydrides 1c-g.Only fluoromaleic anhydride 1b is attacked by cyclohexyl radicals predominantly at the substituted carbon atom, because fluorine is a tiny, electron releasing substituent.Radicals 2 are trapped predominantly from the anti-direction by the H-donor (figure 1), yielding cis-compounds 3as main products.This "contrathermodynamic" stereoselectivity ranges between 2.3 and 19 (table 1).
