Bicyclo octene cations

The stable radical cation of terthiophene end-capped by bicyclo [2.2.2] octene units has been generated by one-electron oxidation, and its crystal structure determined <2006JA14470>. Dimerization of several one-end-blocked l,3-dithienylbenzo[f]thiophenes by chemical oxidation has been reported <2007TL779>. 

Protonation of the hydroxyl and trimethylsilyloxy groups of A and D, respectively, generates carbocations B and E. In B, attack of the methyl-substituted triple bond leads to formation of the preferred linear vinyl cation. Its trapping by the formate ion furnishes the substituted bicyclo[2.2.2]octene C. On the other hand, attack of the silicon-substituted triple bond in E occurs to form the silicon-stabilized p-carbocation, which, on trapping by formate ion, yields the substituted bicyclo[3.2.2]nonene F. 

Cationic cycloadditions. Ionization of p-benzoquinone monoacetals is induced by MejSiOTf in highly polar media (LiClO /EtOAc) and the carbocations are captured in situ by alkenes to give bicyclo[3.2.1]octene derivatives. A synthesis of 2-(l -phenylethoxy)-8-oxabicyclo[3.2.1]oct-6-en-3-one in good enantiomeric purity from furan and a mixed acetal of 2-(triethylsiloxy)acrolein (prepared from pyruvaldehyde dimethylacetal in three steps) is promoted by MejSiOTf. 

Synthesis and properties of cationic -conjugated systems stabilized by bicyclo[2.2.2]octene units including annulated silatropilium ion, thiophene, 1,2-dithiine, 1,4-dithiine, and oligothiophenes 05SL187. 

Other a,co-disubstituted oligothiophenes such as 31 [24], 32 [103], 33 [104], 34 [105], 35 [106] and 36 [98] were characterized by cyclic voltammetry (Scheme 9.23). In 35, bulky bicyclo[2.2.2]octene substituents were introduced to prevent dimerization. Indeed, all oligomers derived from 35 (n = 0, 1, 2, 4) show stable radical cations and dications. In the case of the hexamer derived from 35 with n = 4, the two first one-electron reversible oxidation waves are nearly coalesced ( ox 0. 19, = 0.28 V vs FC/FC+)... 

The polymer had primarily trans configuration and contained the cyclohexane ring in the boat form. On the other side, polymerization of 5-methyl-substituted bicyclo[2.2.2]octene has been carried out with cationic and Ziegler-Natta systems [146] leading to low yields in polymers, probably of mainly vinylic structures. 

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