Synthesis of spiro(2.4)hepta-1,4,6-triene

A two-step synthesis of spiro(2.4) hepta-1,4,6-triene 1 is described. The starting material 2 was synthesized by irradiation of diazocyclopentadiene in the presence of (2-bromovinyl)trimethylsilane. The predominant formation of the trans isomer probably reflects the isomeric composition of the starting alkene (cis:trans ratio {dollar}approx{dollar} 10:90). Elimination of 2 using CsF in dimethyl sulfoxide yielded 1.(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE MAI); Spiro (2.4) hepta-1,4,6-triene is remarkably stable. {dollar}rmsp1H{dollar} and {dollar}rmsp{lcub}13{rcub}C{dollar} NMR data could be obtained at room temperature. The infrared spectrum exhibits a moderately strong absorption at 1713 {dollar}rm cmsp{lcub}-1{rcub}{dollar} characteristic of cyclopropenes.; The ultraviolet spectrum of spiro (2.4) hepta-1,4,6-triene recorded in methanol has {dollar}lambdasb{lcub}rm max{rcub}{dollar} = 254 nm, very close to that reported (257 nm) for 3. This observation is in conflict with theoretical predictions which claim that 1 will experience a small hypsochromic shift resulting from spiroconjugation.(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE MAI)...