DIYNE CYCLIZATION IN CAMPHOR DERIVATIVES - EXPERIMENTAL AND THEORETICAL INVESTIGATION

Derivatives of 3-oxo-camphorsulfonimide (1) with two phenylethynyl gro ups in the endo positions at the carbons C-2 and C-3 were prepared, an d their reactivity towards halogenes and titanium chloride was studied . In every case, the two ethynyl groups led to the annulation of a fiv e-membered ring to the bicyclo[2.2.1] system in an orientation which d epends on the bulkiness of the additional substituent in position 3. N MR studies show that cationic species like 6 and 8 are the first detec table intermediates. They not only contain the fused five-membered rin g but also a bond between its exocyclic methylene carbon and an oxygen atom of the sulfonyl group, thus transferring the positive charge mai nly to sulfur. Semiempirical calculations (PM3) suggest two intermedia tes in the formation of such cations.