SEQUENTIAL PERICYCLIC-REACTIONS OF CYCLOPENTADIENONE WITH NONCONJUGATED DIENES, INTRAMOLECULAR CYCLOADDITION REACTIVITY OF THE DECARBONYLATED PRIMARY CYCLOADDUCTS AND X-RAY STRUCTURE OF DDA ADDUCT

Pericyclic reactions of 2-oxo-1,3-bis(ethoxycarbonyl)-2H-cyclopenta[a]acenaphthylene (Ib) with nonconjugated dienes (2c-k) were investigated. The cyclopentadienone (1b) reacted readily with 2c-k to give [4+2]phi cycloadducts (3c-k) that spontaneously lost carbon monoxide to afford the dihydrohexadiene derivatives (4), some of which underwent intramolecular cycloaddition reaction to give the double Diels-Alder reaction (DDA) cyclodducts (5). The structures of 4 and 5 were determined from spectral data, The intramolecular cycloaddition reactivity of 4 are discussed on the basis of the MNDO-PM3 calculated transition states. The structure of the DDA cycloadduct from 1 and dibenzo[a,c]cyclooctadiene was determined by single crystal X-ray analysis, indicating the presence of moderate bond elongations due to through-bond interaction. The observed data were compared with those derived from the MM and MO-calculated structures.