Organocerium: A New Contender for Halogen–Metal Exchanges

Abstract

In the context of our current research on dependable and sustainable methods for C–C bond-forming reactions, we have recently developed new strategies to generate organocerium reagents through simple bromide–cerium exchanges. n-Bu3Ce enabled a fast and general access to functionalized triaryl- and alkenyl cerium species from the corresponding aryl- and alkenyl bromides. A broad range of these new organocerium species was engaged in Zweifel’s olefination, allowing for the synthesis of widely substituted alkene derivatives in a stereospecific way. Herein, we place the formation of organocerium species in the context of known organometallic reagents (Li, Mg, Zn, Cu, Ca, La, and Sm) generated through halogen–metal exchange reactions and their application in further transformations.

CeCl3/n‐BuLi: Enträtselung von Imamotos Organocer‐Reagenz

“…[12] Im Gegensatz hierzu wurde den heterobimetallischen Organometall-Reagenzien der Hauptgruppenelemente deutlich mehr Aufmerksamkeit geschenkt und legitimierte damit die moderne Chemie der At-Komplexe. [13] Imamoto-artige Seltenerdmetallverbindungen, wie sie kürzlich fürd ie Halogen-Seltenerdmetall-Austauschreaktion [14] oder die Zweifel-Olefinierung [15] eingesetzt wurden, werden üblicherweise in situ erzeugt und wurden mit "n-Bu 2 LaCl•4 LiCl", [16] "n-Bu 3 Sm•5 LiCl" [17] oder einfach "n-Bu 3 Ce" bezeichnet. [15] Diese Formeln wurden mithilfe von EXAFS- [18] oder Raman-Spektoskopie abgeleitet.…”

Recent progress toward the asymmetric synthesis of carbon-substituted piperazine pharmacophores and oxidative related heterocycles

“…On the other hand, exposure of 51 to TBSCl and chloroacetyl chloride followed by cesium carbonate in DMF at 65 °C and sodium hydride at 0 °C to reflux produced imino ketopiperazine 55 through the intermediacy of 54 . Finally, addition of an allyl organocerium reagent to 55 35 gave rise to homochiral trisubstituted piperazinone 56 in 87% yield ( Scheme 8 ).…”

CeCl3/n‐BuLi: Unraveling Imamoto's Organocerium Reagent

“…Imamoto‐type rare‐earth‐metal reagents, more recently employed for halogen‐rare‐earth‐metal exchange reactions [14] or Zweifel olefinations, [15] are as a rule generated in situ and have been designated “ n ‐Bu 2 LaCl⋅4 LiCl”, [16] “ n ‐Bu 3 Sm⋅5 LiCl”, [17] or simply “ n ‐Bu 3 Ce”. [15] The formulas were derived from X‐ray absorption fine structure (EXAFS) studies [18] or Raman spectroscopy.…”