Experimental and computational study of the intramolecular reactivity of free tert-butylphenylmethylene.: Modification of the chemistry of tert-butylmethylene by the introduction of a phenyl group

The chemistry of tert-butylphenylmethylene, 2, has been investigated experimentally and computationally. Free carbene 2 was generated by the thermal rearrangement of p-tert-butylphenylmethylene and observed to rearrange by C-H insertion to give 1,1-dimethyl-2-phenylcyclopropane, 3, and by C-C insertion to yield 2-methyl-3-phenyl-2-butene, 4. An examination of the 3:4 ratio led to the conclusion that C-H insertion is favored over C-C insertion by 1.6 +/- 0.1 kcal/mol in good agreement with a calculated (PMP2/6-31G(d)//MP2/6-31G(d)+ZPC/6-31(d)) value of 2.0 kcal/mol. The S-T gap in 2 is estimated to be 5-6 kcal/mol.