McMurry Coupling of 2-Acylphosphacymantrenes: E- vs Z-Stereochemistry of the 1,2-Bis(phosphacymantrenyl) Alkenes
摘要:
The McMurry coupling of a 2-acetylphosphacymantrene with the TiCl4/Zn couple preferentially provides the Z-alkene as a mixture of the rac and meso, diastereomers. The coupling of the 2-benzoylphosphacymantrene mainly gives the E-alkene together with the 2-benzyl reduction product. The alkene stereochemistries have been established by X-ray crystal structure analyses. A titanium-carbene intermediate is suggested in the second case.