Two-fold extrusion reactions of 1, 3, 4-thiadiazolines 1 provide a convenient stereoselective route to unhindered 2-olefins. An improved preparation of the thiadiazolines involves reaction of an aldehyde with HS-hydrazine, followed by in situ oxidation of the intermediate predominantly trans thiadiazolidine 2. Stereospecific extrusion of nitrogen yields the cis- thiirane which upon treatment with triphenylphosphine affords the corresponding 2-alkene ...
