65424-93-3Relevant 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
Stereoselektivitaet intermolekularer Radikalreaktionen
Giese, Bernd
, p. 993 - 1004 (2007/10/02)
Regio- und Chemoselektivitaeten von Radikalreaktionen sind haeufig hoch und weitgehend vorhersagbar.Systematische Studien haben nun gezeigt, dass auch die Stereoselektivitaet von Radikalen gelenkt werden kann.Anhand von Fuenfring- und Sechsring-Radikalen wird demonstriert, wie sterische und stereoelektronische Effekte die Diastereoselektivitaet der Reaktionen cyclischer Radikale mit Alkenen beeinflussen.Dabei spielen Temperatur und Loesungsmittel sowie die Reaktivitaet der Radikalfaenger eine Rolle; bei geeigneter Wahl der Reaktionsbedingungen kann die Stereoselektivitaet bei cyclischen Reaktanten sehr hoch sein.Nur geringe Stereoselektivitaeten werden haeufig bei Reaktionen zwischen acyclischen Radikalen und acyclischen Alkenen beobachtet.Erste Experimente zeigen, unter welchen Bedingungen auch diese Systeme stereoselektiv reagieren koennen.
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).
