Bishomobenzene

TV-Substituted l,4-dihydro-l,4-diazocines 6 can be obtained by [TC2S + 2S + 2S] cycloreversion from. mi-benzene diimine (cA-bisazirinofa. c]benzene, diaza-c-bishomobenzene) derivatives 5 at room temperature or slightly elevated temperatures.2 - 5 The syn-benzene diimines (3,8-dia-zatricyclo[5.1.0.02,4]oet-5-enes), which are required for the valence isomerization, are available by two methods from benzene oxide derivatives. 

A range of variously substituted cis- and fram -cr-bishomobenzenes has been isolated or prepared as reactive intermediates (see, for example, Prinzbach and Stusche, 1970 Dalrymple and Taylor, 1971 Prinzbach et al., 1971 Whitlock and Schatz, 1971 Prinzbach and Schwesinger, 1972 Hashem and Weyerstahl, 1981) and none of these systems were proposed to be homoaromatics. Similarly, homoaromaticity is not considered to be of any significance in the cyclooctadienyne [110] (Meier et al., 1985). 

Dai et al. (1990) have reported direct spectroscopic measurements on a similar bishomobenzene radical cation. The system they studied was the bicyclo[3.3.0]octa-2,6-diene-4,8-diyl radical cation [159] generated by radiolytic oxidation of semibullvalene [83] in Freon matrices. The hydrogen... 

Several bishomobenzene and trishomobenzene derivatives rearrange on thermolysis to yield cyclooctatriene and cyclononatriene derivatives, respectively. Thus, the c/s-oxabishomobenzene diester 14 exists in equilibrium with the corresponding oxacyclooctadiene diester 15 at 100 °C. ... 

Substituent perturbation of the 3,3-shift equilibrium in SB has been studied, but there has been more of a focus on lowering the barrier so that the transition state for the 3,3-shift might be made more stable than the SB itself. Grohmann made the dimethyl tetraester of Scheme 9.10, which is bright yellow and has a 1.78 A C2-C8 bond distance in the solid state suggesting that the delocalized transition state was accessible.Subsequently Quast provided more examples, and calculations agreed that the bishomobenzene structure for the dimethyl-2,6-dicyano-4,8-diphenylsemibullvalene (Scheme 9.10), gives rise to the blue color in... 

Lithiation of (425) results in carbene insertion and formation of bicyclobutane (426). This latter compound proves to be a valuable synthetic intermediate, affording trans-bishomobenzene (in 30-40 % yield, on a multigram scale) and homotropilidene (Scheme 66). Whereas (427), with no suitable C—H bond available for insertion,... 

A simple conversion of 3-norcarene into trans-bishomobenzene has been discovered. The method involves reaction of (693), itself obtained in two standard steps from 3-norcarene, with Bp3,OEt2. Silver perchlorate-catalysed decomposition of (693) gave 2,3-homotropilidene quantitatively. 

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