New aspects of the thio-Wittig-reaction

Treatment of phosphorus ylides with elemental sulfur, selenium or tellurium ("Staudinger-chalcogenation") leads to the formation of the respective cha lcogenacarbonyls. The reaction of Ph3P=CH2 with thiobenzophenone gives a re active thio-Wittig intermediate that exhibits a pronounced thio-betaine cha racter in polar solvents. A thio-betaine is isolated from the reaction of E t3P=CHCH3 with S=G(C6H4OCH3)(2) and characterized by an X-ray crystal struc ture analysis. The S...P separation in this gauche-betaine is 3.109(5) Angs trom and the S-C-C-P dihedral angle amounts to 47.7(5)degrees.