Rack-mounted chemistry IV: the thermal rearrangement of 7-oxabenzonorbornadienes into benzo[b]oxepines on and off the polycyclic rack |
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Authors: | Muhong Shang Douglas N Butler Ronald N Warrener Davor Margeti? |
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Institution: | 1. Centre for Molecular Architecture, Central Queensland University, North Rockhampton, 4701 Queensland, Australia;2. Division of Organic Chemistry and Biochemistry, Ru?er Boškovi? Institute, Bijeni?ka c. 54, 10000 Zagreb, Croatia |
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Abstract: | The thermal rearrangement of 3]polynorbornane bis-imide rack-mounted 7-oxabenzonorbornadienes has been conducted using flash vacuum pyrolysis (FVP) at 520 °C and is compared with the FVP of similar 7-oxabenzonorbornadienes off the rack. The isomerisation is considered to involve (a) C–O bond cleavage to a vinylogous 1,5-dipole, (b) formation of a benzene epoxide by nucleophilic ring-closure and (c) valence-isomerisation of the benzene epoxide to the oxepine. Competing fragmentation to the isobenzofuran by ejection of acetylene and other rearrangements become prominent pathways off the rack, whereas isomerisation to the oxepine is highly favored on the rack. |
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Keywords: | Retro-Diels&ndash Alder Pyrolysis Isobenzofurans Molecular racks Rearrangement |
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