PHOTOCHEMICAL FUNCTIONALIZATION OF CUBANES

A wide range of cubanecarboxylic acids has been prepared by a simple and efficient photochemical process. Chlorocarbonylation of cubanecarboxylic acid with oxalyl chloride under UV irradiation produced polysubstituted cubanes with chlorocarbonyl groups predominantly on the remote sites (beta or gamma). The T-d-tetraacid chloride 6b, in which chlorocarbonyl groups are in alternate positions, was the major product. Irradiation of 1,2,3,7-tetrasubstituted cubane 9 with oxalyl chloride gave pentasubstituted cubane 10. Other isomers, 1,3,5,7-tetrasubstituted cubane 6 and 1,2,4,7-tetrasubstituted cubane 8, in which chlorocarbonylation would occur at positions ortho to three or two carbonyl groups, gave only chlorinated products. Photochemical reaction of oxalyl chloride with nitrocubanes gave chlorocarbonylated and chlorinated nitrocubanes. Ab initio calculations show carbon-hydrogen bond strength at different positions of the cubane is not the major factor in determining the regioselectivity of the chlorocarbonylation. A polar effect might be the key factor in site selectivity.