Alternative General Synthetic Routes to [2.2]Cyclophanes and [3.2]Cyclophanes from [3.3]yclophane-2,11-diones by Photodecarbonylation, and a Structural Study of [3.2]Metacyclophanes

摘要

Photodecarbonylation of [3.3]cyclophenae-2,11-diones, which are readily prepared by TosMIC coupling, affords [2.2]cyclophanes in high yield. This method also provides a general synthetic method for [3.2]cyclophan-2-ones by taking advantage of the fact that this photochemical reactionproceeds in a stepwise manner through [3.2]cyclophan-2-ones. A series of [2.2]cyclophanes, [3.2]cyclophanes, and [3.3]cyclophanes can thus be made available fromthe dommonprecursor [3.3]cyclophane-2,11-diones. In sharp contrast to the preferred syn geometry of [3.3]methacyclophanes, [3.2]metacyclophanes adopt anti geometries and the aryl ring inversion process is observed by variable-temperature ~1H NMR spectroscopy. In the crystalline state, the two aryl rings of anti-[3.2]metacyclophanes are almost parallel inspite of the unsymmetrical bridge length; they overlap only at the C-9 and C-17 positions, and the transannular distances are shorter than the corresponding distances in [3.3]metacyclophane-2,11-dione.