Radikalische CC-Verknüpfung nach der „Zinnmethode” – ein breit anwendbares Verfahren

Abstract

Das vielfältig nutzbare Tributylzinnhydrid bewirkt als Katalysator (in Gegenwart von NaBH4) die radikalische Kettenverlängerung von Alkyliodiden mit Acrylonitril oder Alkenen, die z. B. Keton‐, Aldehyd‐, Ester‐ oder Phenylsubstituenten enthalten. Als Reagens ermöglicht Tributylzinnhydrid eine bequeme Synthese C‐verzweigter Desoxyzucker. Dazu wird ein Zucker wie 1, Y = OH, in ein Xanthogenat oder Thiourethan umgewandelt, das z. B. mit Acrylonitril zu 2, R = CH2CH2CN, reagiert.

The use of free radical initiators bearing metal–metal, metal–hydrogen and non-metal–hydrogen bonds in synthesis

“…)-NaBH 4 (Scheme 30). 154 The use of only 0.2 equivalents of Bu 3 SnCl ensures a low concentration of Bu 3 SnH is generated (from reduction 155 using NaBH 4 ), which in turn, minimises the amount of simple reduction leading to cyclohexane (which has a rate constant of around 10 6 dm 3 mol Ϫ1 s Ϫ1 at rt). Hence, radical addition to the double bond (k ≈ 10 5 dm 3 mol Ϫ1 s Ϫ1 at rt) occurs followed by hydrogen-atom abstraction (∼10 5 dm 3 mol Ϫ1 s Ϫ1 at rt) in preference to slower radical addition to another molecule of the alkene (∼10 3 dm 3 mol Ϫ1 s Ϫ1 at rt) leading to a polymer.…”

Radical Amination with Sulfonyl Azides: A Powerful Method for the Formation of CN Bonds

“…The use of free‐radical reactions in multistep synthesis has steadily increased over the last years, mainly because of their compatibility with a large number of functional groups and their high potential for performing sequential transformations 1. A lot of effort has been concentrated on the development of chain reactions for the formation of carbon– carbon bonds under reducing (Giese reaction)2 or atom transfer (Kharasch–Curran)3, 4 conditions. Formation of carbon–nitrogen bonds by means of a radical pathway is highly attractive for the synthesis of alkaloids and related heterocyclic compounds.…”

Temperature Dependence of the Radical Addition to Alkenes

“…The radicals were generated from alkyl mercuric salts with NaBH 4 [7] and from alkyl iodides with Bu~nH [8] . The radicals were generated from alkyl mercuric salts with NaBH 4 [7] and from alkyl iodides with Bu~nH [8] .…”

“…• Author to whom correspondence should be addressed. The radicals were generated from alkyl mercuric salts with NaBH 4 [7] and from alkyl iodides with Bu~nH [8] . In both reactions a radical chain reaction is carried out in which alkyl radicals 2 attack alkenes 3 to give adduct radicals 4 that yield products 7 by quantitative trapping with hydrogen donors Sand 6.…”