Olefin synthesis by two-fold extrusion processes. Part II. Synthesis of some very hindered olefins

Reaction of hindered thiones with hindered diazo-compounds affords Δ3-1,3,4-thiadiazolines, which by two-fold extrusion afford in good yield very hindered olefins. In this way 2-diphenylmethylenebornane (VI), 2-diphenylmethylene-1,3,3-trimethylnorbornane (VIII), 1,1-di-t-butyl-2,2-diphenylethylene (XII), and 2-di-t-butylmethylenebornane have been prepared. The latter is probably the most hindered olefin prepared to date. The steric limitations of this approach have been explored. It was not possible to obtain in this way tetra-t-butylethylene (XIV) or 2-di-t-butylmethylene-1,3,3-trimethylnorbornane (XV).