Cyclooct‐1‐en‐5‐yne. Preparation, spectroscopic characteristics and chemical reactivity

Abstract

Cyclooct-1-en-5-yne (3) has been obtained as an isolable, but highly reactive hydrocarbon by oxidation of cyclooct-5-ene-1,2-dihydrazone with lead tetraacetate (Scheme 2). Information regarding the structure and conformational mobility of 3 has been gained from the analysis of its 'Hand I3C-NMR. spectra and was found to agree with the results of force field calculations. Photolysis (206 nm) of 3 in solution has induced cleavage to butatriene and butadiene. The first band in the photoelectron spectrum of 3 (I, 9.10 eV) is attributed to ionization from a rather delocalized orbital with predominant weight of the double bond p-AO's. Nevertheless, the high reactivity of 3 stems from the strained triple bond as evidenced by the reaction products obtained by pyrolysis, oxidation, Diels-A lder addition, and 1,3-dipolar addition (Scheme 4).

The planar dehydro[8]annulenes

“…Wirz triene. Cyclooct-l-en-5-yne (5) has also been reported, 17 and it is less stable than 4. Moreover, Meier and his co-workers have recently observed that cycloocta-1,5dien-3-yne (6)18 is sufficiently stable for it to be isolated as a crystalline compound.…”