PHOTOCHEMICAL FUNCTIONALIZATION OF CUBANES

A wide range of cubanecarboxylic acids has been prepared by a simple a nd efficient photochemical process. Chlorocarbonylation of cubanecarbo xylic acid with oxalyl chloride under UV irradiation produced polysubs tituted cubanes with chlorocarbonyl groups predominantly on the remote sites (beta or gamma). The T-d-tetraacid chloride 6b, in which chloro carbonyl groups are in alternate positions, was the major product. Irr adiation of 1,2,3,7-tetrasubstituted cubane 9 with oxalyl chloride gav e pentasubstituted cubane 10. Other isomers, 1,3,5,7-tetrasubstituted cubane 6 and 1,2,4,7-tetrasubstituted cubane 8, in which chlorocarbony lation would occur at positions ortho to three or two carbonyl groups, gave only chlorinated products. Photochemical reaction of oxalyl chlo ride with nitrocubanes gave chlorocarbonylated and chlorinated nitrocu banes. Ab initio calculations show carbon-hydrogen bond strength at di fferent 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.