Tetrabenzo carbonization

A difference CD method can be used to determine the absolute configuration of the allylic position in polyols. The difference CD spectrum between the allylic tetrabenzoate 12 and saturated tetrabenzoate 13 displays a negative Cotton effect, Ae —4.9 (224 nm), thus establishing R configuration of the allylic carbon atom (Figure 18)154. 

Very efficient reaction occurs when phenyl 1 -thio-/ -D-glucopyranoside and -D-galactopyranoside tetrabenzoates (94 and 95) are treated in refluxing carbon tetrachloride with JV-bromosuccinimide under a heat lamp, and, within 15 minutes, they are converted into products from which the enones 96 and 97 have been obtained by direct crystallization in 76 and 83% yield, respectively (see Scheme 15).20... 

In another metal-mediated coupling reaction, the highly functionalized dienes 136a and 136b were allowed to react with Ni(PPh3)4 in the presence of excess zinc/copper couple at 50 ""C and 1 atm of carbon monoxide to provide the octakis(methoxycarbonyl) 137a and the tetrabenzo derivatives 137b in excellent yields (77 and 84%, respectively), (see Scheme 17 compare also Scheme 12 for the formation of the related [4]radialene 10686-88) 373 s treated with excess LiBr H2O in HMPA at temperatures... 

Boese, R Matzger, A.J Volhardt, K.P.C. Synthesis, crystal structure, and explosive decomposition of 1,2 5,6 11,12 15,16-tetrabenzo-3,7,9,13,17,19-hexa-dehydro[20]annulene formation of onion- and tube-like closed-shell carbon particles. J. Am. Chem. Soc. 1997, 119, 2052-2053. 

Replacing one heptagon in 21 with a pentagon leads to tetrabenzo[5,7] fulvalene (31), as shown in Figure 4.9, which was studied by the Mills group for the examination of aromaticity/antiaromaticity within the same carbon framework [34,35]. Oxidation of 31 with SbFj in SO2CIF yielded the dication (31 " ), which was found to contain an antiaromatic fluorenyl cation as indicated by a paratropic shift in the NMR spectrum and an aromatic dibenzotropylium cation. Reduction of31 with lithium resulted in the dianion (31 ), which was characterized with NMR... 

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