Rapid Vinyl Shifts in Spiro[4.4]polyenes: Verification of the Rate-Determining Step and the Identity of the Migrating Group

Pyrolysis studies of 1, 2, 3, 4-tetradeuteriospiro[4.4]nona-1, 3, 6-triene (10) show that the 1, 5-sigmatropic shift proceeds with negligible primary deuterium isotope effect, eliminating a rate-determining H shift in this multistep rearrangement. Pyrolysis of 1, 2, 3, 4-tetramethylspiro[4.4]-nona-1, 3, 6-triene leads to specific vinyl migration, thereby establishing preferential vinyl as opposed to alkyl migration. The structure of the pyrolysis product was determined by an X-ray diffraction structure determination on a crystalline adduct with dimethyl 3, 6-dicarboxy-1, 2, 4, 5-tetraazabenzene; the adduct is the result of an unprecedented reaction of the tetrazine.