Rearrangement of 1-noradamantyl and 1-adamantylcarbene to bridgehead alkenes: Lifetimes of two bridgehead carbenes in solution

B3LYP density functional calculations with the 6-31G* basis set predict tha t 3-noradamantylcarbene 7 rearranges to adamantene 9 and protoadmant-3-ene 10 over barriers of 0.35 and 7.84 kcal/mol, respectively, after zero-point energy correction. The same level of theory predicts that 1-adamantylcarben e 8 rearranges to homoadamantene 11 over a barrier of 6.06 kcal/mol after z ero-point energy correction. To test these predictions, the photochemistry of 3-noradamantyldiazirine 5 and 1-adamantyldiazirine 6 was studied. Photol ysis of 5 and 6 in cyclohexane produces the known dimers of the strained al kenes. 1-Adamantylcarbene 8 can be trapped in solution with cyclohexane and piperidine. 1-Adamantylcarbene 8 can be trapped with pyridine to form an y lide upon laser flash photolysis (LFP) of 6. 3-Noradamantylcarbene 7 cannot be intercepted with pyridine in LFP experiments. 3-Noradamantylcarbene 7 i s not trapped with cyclohexane and is trapped with piperidine in only minis cule yield. The data indicates that 1-adamantylcarbene 8 is formed more eff iciently from its diazirine precursor than is 3-noradamantylcarbene 7 and t hat the solution-phase lifetime of 1-adamantylcarbene 8 is at least 10 time s longer than that of 3-noradamantylcarbene 7.