Spiro[4.4]nonatetraene and spiro[4.4]nona-1,3,7-triene. Synthesis and properties. Effects of spiroconjugation

Spiro[4.4]nonatetraene (1) was prepared for the first time by a relatively direct synthesis starting from allyl bromide and diethyl malonate. Spiro[4.4]nona-l,3,7-triene (2) was obtained by a new route, starting from cyclopentadienide anion and 4,5-di(bromomethyl)-2,2-dimethyl-l,3-dioxolane (16). Comparison of the spectral and chemical properties of 1, 2, and spiro[4.4]nona-l,3-diene (10) revealed significant effects of spiroconjugation. The uv spectrum of 1 showed a red shift of 22 nm and lowered extinction coefficient compared to 2 and 10, com-pletely consistent with earlier theoretical predictions.