Sulfuranes Lacking Benzoannelation. Sulfuranes and Other Hypervalent Molecules Studied by (17)O-NMR

The rates of hydrolysis of benzoannelated vs nonbenzoannelated sulfuranes, viz. 5 vs 3 or 5 vs 4, were compared. Benzoannelation was found to provide very modest kinetic stabilization. Crystal structures of sulfuranes 3 and 4 were obtained and compared with each other, with a dibenzoannelated sulfurane, 17, and with a non-sulfurane analogue of 4. Bond length variations could be understood in the context of simple resonance arguments. (17)O NMR studies of 3-5 showed that this technique was indeed sensitive to sulfurane structure. For example, the chemical shifts of the two carbonyl oxygens of 4 differed by over 20 ppm. Other hypervalent systems, mainly iodinanes, were studied by (17)O NMR. A variety of theoretical methods were surveyed to test how well they could reproduce the geometry of 3. Density functional theory calculation outperformed ab initio geometry optimization at the MP2/3-21G() level. Finally, a cis-trans isomerization of the double bond of 11 and one of the two double bonds of 10 was studied.