PHOTOEQUILIBRATION OF 2-NAPHTHYLCARBENE AND 2,3-BENZOBICYCLO[4.1.0]HEPTA-2,4,6-TRIENE

Irradiation (lambda > 300 nm or lambda = 480 +/- 6 nm) of 2-naphthyldiazomethane (4), matrix-isolated in argon at 10 K, gives a mixture of 2-naphthylcarbene (1) and 2,3-benzobicyclo[4.1.0]hepta-2,4,6-triene (2). 2-Naphthylcarbene (1) is characterized by infrared, UV/visible, and ESR spectroscopy and by chemical trapping with CO. 2,3-Benzobicyclo[4.1.0]hepta-2,4,6-triene (2) is characterized by infrared and UV/visible spectroscopy. A photoequilibrium exists between carbene 1 and bicyclic compound 2. Photolysis (lambda = 290 +/- 6 nm) of bicyclic compound 2 results exclusively in ring-opening to carbene 1. Similarly, photolysis (lambda = 560 +/- 6 nm, 360 +/- 6 nm, >360 nm) of carbene 1 results exclusively in cyclization to bicyclic compound 2. Thus, the photochemistry of 2-naphthylcarbene contrasts with that of phenylcarbene; 2-naphthylcarbene (1) cyclizes to bicyclic compound 2, while phenylcarbene ring-expands to give 1,2,4,6-cycloheptatetraene.