3c-g, while 4b is photostable under the same conditions. The photochemical 4-3 rearrangement is completely reversible: infrared irradiation or visible light irradiation (A> 470 nm) of the cyclopropenea 3 lead back to triplet carbenea 4 quantitatively. In addition, several of the 1, Sbridged cyclopropenea 3 undergo a thermal rearrangement to give carbenes 4. This indicates that the highly strained cyclopropenes 3 are thermodynamically lese stable ...
