Stereoelectronic Effects in Vinyl Sulfoxides

Though vinyl sulfoxides behave in some respects like alpha,beta-unsaturated carbonyl compounds, the mode of stabilization is significantly different. Interaction of the C=C double bond (acting as a donor) with the electron-withdrawing S=O bond is only possible when the p orbitals of the double bond are collinear with the S-O sigma* orbital. The maximum UV absorbance wavelengths in conformationally constrained substrates bearing an S=O bond collinear with the p orbitals of a C=C double bond are 2-14 nm higher than those in analogous compounds with a roughly orthogonal sulfoxide moiety. Similarly, a lone pair evolving during nucleophilic attack on vinyl sulfoxides is stabilized only if it is oriented anti to a S=O bond, which has significant impact on the stereoselectivities and reaction rates for nucleophilic attack on vinyl sulfoxides. The differing reaction rates of differently configured vinyl sulfoxides were measured in a competition experiment.