Bishomoaromatic compounds

A valence bond isomer of pentakis-(trifluoromethyl)-l, 3-diazepine (44) was prepared from (43) (81TL1113) (44) can be transformed thermally or photochemically to a 2,4-diazabicyclo(3.2.0)hepta-2,6 diene (45), which was subsequently photolysed to an imidazole in an anionic process. Compound (45) is highly acidic arising out of the bishomoaromaticity of the anion and forms a salt with Et3N (81TL1369). 

Bishomoaromatic stabilization energies [(35) -> (36)] were obtained by computational methods this study was part of a paper describing the experimental preparation of a zwitterionic analogue of such compounds (i.e. where X is boron).76... 

A number of studies of a-elimination have employed 9,9-dibromobicyclo[6,l,0]-nonyl derivatives and one has led to optically active cyclonona-2,3-dienone. Loozen and his group have found that whereas endo-a ky atior of the 9,9-dibromo-bicyclo[6,l,0]-nonanes and -nona-2,4,6-triene can be effected, compounds (398) and (399) afford allenes under the same reaction conditions. This has been ascribed to bishomoaromatic interaction favouring facile disrotatory cleavage of the carbenoid as depicted by (400). Under different conditions, Baird and Reese have found that the A -isomer of (398), the 3,5-diene, and (401) yield allenes and not carbene re-... 

The dication 29 could be considered a sandwich bishomoaromatic dication or a 4 jr-electron longicyclic aromatic system or as the alternative homoaromatic species 30. To resolve this problem, Olah and Prakash et al. undertook a theoretical study of these compounds and also, for comparison, monocation 31. Using HF/6-31G and B3LYP/6-31G methods, they obtained optimized structures for 29—31. There is no evidence for longicyclic stabilization in 29, and both... 

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