MODE OF ATTACK OF ATOMIC CARBON ON BENZENE RINGS

Reaction of are generated carbon atoms with tert-butylbenzene, 4, give s 3-methyl-3-phenyl-1-butene, 5, and 1,1-dimethylindane, 6. Labeling s tudies and isotope effects demonstrate that 5 results from an insertio n into a methyl C-H bond followed by 1,2 hydrogen shift while 6 arises from initial ortho C-H insertion followed by intramolecular insertion into a methyl C-H bond. When fluoroboric acid is added to the 77 K ma trix of 4 + C, tert-butyltropylium fluoroborate, 18, is formed. Labeli ng studies indicate that 18 results from initial insertion of C into m eta and para C-H bonds of 4 followed by ring expansion to cycloheptate traenes which are subsequently protonated. The reaction of C with benz ene gives similar results, indicating that initial C-H insertion is th e preferred mode of attack of atomic carbon on benzene rings.