Chirality Control in Planar Chiral Cobalt Oxazoline Palladacycles

详细信息    查看全文

• 作者：Doyle J. Cassar ; Hemin Roghzai ; Didier Villemin ; Peter N. Horton ; Simon J. Coles ; Christopher J. Richards
• 刊名：Organometallics
• 出版年：2015
• 出版时间：June 22, 2015
• 年：2015
• 卷：34
• 期：12
• 页码：2953-2961
• 全文大小：472K
• ISSN：1520-6041

文摘

Palladation of (畏⁵-(S)-2-(4-R-substituted)oxazolinylcyclopentadienyl)(畏⁴-tetraphenylcyclobutadiene)cobalt(I) with Pd(OAc)₂ (R = Me, CH₂Cy, CH₂i-Pr, CH₂Ph) resulted exclusively in formation of the (S,S_p)-palladacycle with R = CH₂Cy (acetic acid solvent) and up to 13:1 selectivity in favor of the (S,S_p)-palladacycle with R = CH₂i-Pr (CH₂Cl₂ solvent). In the latter case diastereomeric purity was achieved by recrystallization, and the absolute configuration of the new element of planar chirality was established by X-ray crystallography. These outcomes contrast with the opposite sense of diastereoselectivity observed for the corresponding R = i-Pr-substituted oxazoline, which results in the palladacycle (S,R_p)-COP-OAc (acetic acid solvent), these palladation reactions being under either kinetic (S,S_p) or thermodynamic (S,R_p) control. Following conversion to the chloride-bridged (S,S_p)-palladacycle dimer (R = CH₂Cy), this was employed as a catalyst for the rearrangement of allylic trichloroacetimidates (0.25 mol % catalyst loading, up to 80% ee).