Abstract
2,6-Dimethyl-2,7-octadienal (1) undergoes a BF3-catalyzed reaction to give exo-4,8-dimethyl-2-oxabicyclo- [3.3.1]non-3-ene (4) in 49% yield. Adduct 4 is probably formed by a Lewis acid catalyzed inverse-electron-demand Diels-Alder reaction in which the ,/3-unsaturated aldehyde functions as the diene. Upon pyrolysis of 1 at moderate temperatures (~370 °C), a 1:4:1 kinetically controlled mixture of Diels-Alder adduct 2 and cis substituted ene adducts 14 and 15 are formed. At higher temperatures (405 °C), complex mixtures of Diels-Alder adducts 2, 4, and 9 and ene adducts 14-18 are formed.