Reaction of an Enantiomerically Pure Phosphaalkene-Oxazoline with MeM Nucleophiles (M = Li and MgBr): Stereoselectivity and Noninnocence of the P‑Mesityl Substituent

• Published in: Organometallics Vol. 33; no. 24; pp. 7215 - 7222
• Main Authors: Serin, Spencer C, Patrick, Brian O, Dake, Gregory R, Gates, Derek P
• Format: Journal Article
• Language: English
• Published: American Chemical Society 22-12-2014
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om501008m

The addition of alkyl nucleophiles (MeM, M = Li, MgBr) across the PC bond of an enantiomerically pure phosphaalkene-oxazoline followed by protonation of the C anion affords phosphines with three chirality centers. The formation of palladium(II) complexes of the resultant phosphines permitted structural characterization of the products by X-ray diffraction. The choice of nucleophile has a profound effect on the product distributions. For instance, the Grignard reagent adds in a diastereoselective manner to give one major phosphine product with P- and C-stereocenters. In contrast, addition of methyllithium has proven not only to be less stereoselective but also affords a fascinating cyclic phosphine product. Both the Grignard and RLi reactions involve proton transfer from the o-Me of the P-Mes substituent even though the products are quite different in each case.