The Influence of the Axial Chirality of Dibenzo[a,c]cyclooctene on the Configuration of Its Photo-Diels-Alder Adducts

Triazole-diones and naphthoquinone are shown to add in a photochemical [4+2] reaction to the strongly twisted title diene 1 . With 1, 4-naphthoquione, the process is also accompanied by a [2+2] cycloaddition. When the pure atropisomer (?)- 1 is irradiated in presence of 2, 3-dichloro- 1, 4-naphthoquinone ( 9 ), the axial chirality of the diene is preserved. Moreover, it is found to exert complete control over the chirality induced in the resulting spiro-dihydropyrane 10 . Absolute configuration are determined by X-ray crystallography. In absence of a photo-dienophile, the axially chiral, dextrorotatory 6-phenyldibenzo[a,ccyclootene] ((++)- 11 ) undergoes a stereospecific electrocyclization to give levorotatory 4b,6a-dihydro-5-phenylcyclobuta[l]phenanthrene ((?)- 13 ). Thus, only one out of two possible, disrotatory modes of ring closure is preferred.