The Preparation of Helical Cyclophanes Containing Five-membered Rings

Abstract

Cycloadditions between the indenone derivatives prepared in situ from the bromides 12a and 12b and 4-vinyl[2.2]paracyclophane (11) yielded the Diels−Alder adducts 13a and 13b in acceptable yields. When these were heated in the presence of DDQ in toluene, the fluorenophanes 14a and 14b were produced in good yields. The diol 17 obtained from the tetralonophane 15 on treatment with POCl3/pyridine was dehydrated to the diene 18, which could be trapped by p-benzoquinone (19) to provide the cycloadducts 20 and 21; the former was oxidized to the latter by DDQ treatment. Although the even more highly annelated helical phane system 22 could be prepared from 17 and 12a, its aromatization to the ketone 24 or the hydrocarbon 25 failed. All new compounds were characterized by their spectroscopic data, in particular by extensive NMR investigations. A single-crystal X-ray structure analysis for the parent hydrocarbon phenanthreno[2.2]paracyclophane (5) is reported.