COMPLETELY SPIROCYCLOPROPANATED MACROCYCLIC OLIGODIACETYLENES - THE FAMILY OF EXPLODING [N]ROTANES

A general approach to the family of completely spirocyclopropanated macrocyclic polydiacetylenes, that is, cyclic dehydrooligomers of 1,1-diethynylcyclopropane 4, is reported. The characterized examples of these ''exploding'' [n]rotanes are for n = 5, 6, 7, 8, 9, 10, and 12. X-ray crystal structure analyses for the hydrocarbons with n = 5, 6, 7, and 8 disclose a strong electronic interaction between the cyclopropane and the acetylene units leading to a significant shortening of the distal and lengthening of the proximal cyclopropane bonds. While the five-sided compound 18 can occur as a planar or envelope-shaped molecule, depending on the solvent from which crystals are grown, the six- (19), seven- (20), and eight-sided (21) molecules al have chair conformations. While the butadiyne units in 18 and 19 are bent slightly outwards, those in the seven- and eight-sided molecules 20 and 21, respectively, are bent distinctly inward. All these compounds are extremely high-energy molecules: when struck with a spatula or a pestle, they go off with a puff to yield black soot.