Lithium Malonate Enolates as Precursors for Radical Reactions − Convenient Induction of Radical Cyclizations with either Radical or Cationic Termination
✍ Scribed by Ullrich Jahn; Philip Hartmann; Ina Dix; Peter G. Jones
- Publisher
- John Wiley and Sons
- Year
- 2001
- Tongue
- English
- Weight
- 796 KB
- Volume
- 2001
- Category
- Article
- ISSN
- 1434-193X
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✦ Synopsis
Lithium malonate enolates 4 or 13 are oxidized to the corresponding radicals by ferrocenium hexafluorophosphate (1) or CuCl 2 (2). Trapping by TEMPO (5) to produce 6, dimerization to 7, or radical 5-exo cyclizations are possible subsequent reaction steps following radical generation. The structure of the radical cyclization acceptor determines the outcome of the overall reaction sequence. Tertiary benzylic, alkyl, and α-alkoxy radicals are oxidized by 1. The carbenium ions are stabilized by nucleophilic trapping or deprotonation to give compounds 14 and 18. Secondary alkyl and vinyl radicals are not oxidized and, in the absence of trapping reagents, form radical-derived products. Radical 5-exo cyclization of 13 in-
Consequently, reaction sequences in which multiple intermediates of different oxidation states may be selectively generated and allowed to react are potentially much more attractive [Equation ( 2 )]. [2] This process amplifies the applicability of these intermediates and opens up complementary reaction channels in reaction sequences. Moreover, such