Carbomer of Benzene - A Tour de Force

Significance

Chauvin and co-workers report the first synthesis of hexaalkynyl [6]pericyclyne and carbobenzene. The selected method involves an [8+10] ring formation that proved to be efficient for the preparation of other [6]pericyclynes. The final step in the synthesis is a reductive aromatization that was achieved by the use of only two equivalents of Co₂(CO)₈. Subsequent treatment with SnCl₂/HCl and direct oxidative decomplexation with ceric ammonium nitrate (CAN) afforded the hexaalkynyl carbobenzene in 12% yield over three steps. The ¹H NMR spectrum showed that the triethylsilyl groups are particularly deshielded as a result of a remote ring-current effect. The attempted desilylation of hexa(trialkylsilyl) carbobenzene with tetrabutylammonium fluoride afforded only insoluble black material.