82. “The Influence of the Axial Chirality of Dibenzo[a,c]cyclooctene on the Configuration of Its Photo-Diels-Alder Adducts”
    Burger, U.; Lottaz, P.-A.; Millasson, P.; Bernardinelli, G.
    Helv. Chim. Acta 1994, 77, 850-858.

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.

DOI : 10.1002/hlca.19940770324 

archive ouverte unige:130492