Homoaromatic trishomoaromatic

Monohomoaromatic neutral species 296 Bishomoaromatic neutral systems 299 Trishomoaromatic neutral systems 308 Higher homoaromatic neutral systems 311 Homoaromaticity in the bridged annulenes 312 Other neutral homoaromatic systems 313... 

The trishomoaromatic 1,3-dehydro-5-adamantyl cation [52] has been invoked to explain the extremely high reactivity of the bromide [53] (Scott and Pincock, 1973). Recent calculations suggest that [52] does indeed enjoy homoaromatic stabilization to the extent of 25.4 kcal mol1 relative to the 1-adamantyl cation and 1,3-dehydroadamantane (Bremer et al., 1987). 

Sakurai et al. (1984) prepared a series of silyl substituted potentially trishomoaromatic acetylenes [120]-[123], However, no evidence supporting homoaromaticity was reported. 

There are no neutral molecules with trishomoaromatic character. This is not surprising, given the small size of the resonance energies associated with neutral homoaromatic molecules and the magnitude of the strain effects associated with a potential trishomoaromatic system. 

Cyclic organoboranes containing mnltiple boron atoms within the ring stracture have been extensively stndied as precursors to (multidecker) transition-metal complexes and to nonclassical organoboranes (see Boron Metallacarbabo-ranes and Boron Polyhedral Carboranes). Earlier efforts have been thoroughly reviewed. Recently, a series of triboracyclopentane derivatives were reported by Bemdt and Schleyer (Scheme 6). " Reduction of these boracy-cles gave the nonclassical bishomoaromatic anions (28) and homoaromatic dianions (29). Related trishomoaromatic dianions obtained via reduction of 1,3,5-triboracyclohexane derivatives with lithium were studied by Siebert and Schleyer. i 5> ... 

For further discussion of homoaromatic systems, see (a) McEwen, A. B., Schleyer, P. v. R. (1986). In-plane aromaticity and trishomoaromaticity a computational evaluation. Journal of Organic Chemistry, 51,4357-4368. (b) Allan, C. S. M., Rzepa, H. S. (2008). Chiral Aromaticities. A Topological Exploration of Mobius Homoaromaticity. Journal of Chemical Theory and Computation, 4, 1841-1848. (c) Allan, C. S. M., Rzepa, H. S. (2008). Chiral Aromaticities. AIM and ELF Critical Point and NICS Magnetic Analyses of Mobius-Type Aromaticity and Homoaromaticity in Lemniscular Annulenes and Hexaphyrins. Journal of Organic Chemistry, 73, 6615-6622. 

Monohomoaromatic Bishomoaromatic Trishomoaromatic Fig. 4.3 Cationic, anionic, and neutral homoaromatic molecules... 

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