A General Base Condensation of Diynes to a Spirocyclopropenyl System.

: When a cold (200 K) THF solution of 1,6-heptadiyne is exposed to potassium tert-butoxide, in the presence of 18-crown-6, a green, EPR active solution is spontaneously formed. The intensity of the EPR signal can be augmented by exposure to alkali metal. Analysis of the EPR splitting pattern indicates that the signal originates from the anion radical of 7,14-di-trans-1,5- [14]annuldiyne. Allowing the green-colored solution to warm to ambient temperatures causes an immediate color change (to deep purple) and loss of the EPR activity. Reduced pressure distillation of the solution affords a colorless THF solution containing (spiro[2.6]nona-2,6,8-triene), which is only the second spirocyclopropene compound reported. The base condensation of the diyne is of a general nature as the same spirocyclopropenyl system is obtained from 1,6-heptadiyne, 1,7-octadiyne, and 1,8-nonadiyne. Laser irradiation (337 nm) of tungsten hexacarbonyl in the presence of the spirocyclopropenyl compound yields the stable organometallic: eta2-olefin pentacarbonyl complex.