Oxidation with barium manganate of the enol of dicyanobenzoquinone of meso-17 yields (E)-7b and an isomer (77:23) which was assigned structure (Z)-7b on the tetraacetylethane (10) affords tetraacetylethylene (7a) in good yield. Treatment of the 1,3-diketones 15a and b with basis of spectroscopic evidence. -Tetraacetylethylene (7a) reacts with 1,2-dimethylenecyclohexane to afford two iodosobenzene in the presence of boron trifluoride does not result in oxidative coupling yielding 10 and diacetyl-different [4+2]cycloadducts, viz. the spirocyclic dihydropyran 25 (30 %) and the tetraacetyloctalin 27. Whereas the latter is dibenzoylethane 17, respectively, as has been reported by Moriarty et al. Instead the known difluoroborylenolates 16 stable, the former isomerises to the latter on heating. Formation of both [4+2]cycloadducts and the isomerisation are formed. Oxidative coupling of the sodium enolate of 15b with iodine affords the meso-tetraketone meso-17 and 25 Ǟ 27 are interpreted by invoking the zwitterion 26 as common intermediate. Monoolefines that cannot generate diacetyldibenzoylethylene (E)-7b besides small amounts of rac-17 and the bisenol 19. In the presence of 1,4-stable carbenium ions don't give [4+2]cycloadducts with 7a. In contrast, α-methylstyrene yields the oxa Diels-Alder diazabicyclo[2.2.2]octane, meso-17 and 19 tautomerise yielding identical equilibrium mixtures of meso-17, rac-17, product 30. The structures of (E)-7b, 19, 25, and 27 are established by X-ray diffraction analyses. and 19 (26:29:45). Dehydrogenation with 5,6-dichloro-2,3-