Direct Configurational Correlation of Sulfoxides and Phosphine Oxides by Intersystem Matching of Cotton Effects.

摘要

In the course of studies on the circular dichroism (CD) of phosphine oxides prepared by the Grignard synthesis, it was discovered that there exists a striking overall correspondence between the two sets of spectra consisting of the CD curves of three isomeric anisyl p-tolyl sulfoxides and anisylmethylphenylphosphine oxides in isooctane. All six compounds were prepared by the Grignard displacement reaction, the sulfoxides from menthyl(S)-p-toluenesulfinate, the phosphine oxides from menthyl(S)-methylphenylphosphinate; the sulfoxides and phosphine oxides therefore have the S configuration at sulfur and phosphorus, respectively. This finding is a spectacular confirmation of the independently arrived at absolute configurational assignments. This intersystem matching of Cotton effects also provides striking evidence that the lone pair on sulfur in the anisyl p-tolyl sulfoxides is not significantly implicated in the generation of the optically active transitions, since the transition energy of the P-CH3 sigma-bond pair in the analogous phosphine oxides is expected to be quite high compared to that of n or pi electrons in the molecule.