Y. Tobe et al., [2+2] cycloreversion of [4.3.2]propella-1,3,11-trienes: An approach to cyclo[n]carbons from propellane-annelated dehydro[n]annulenes, J AM CHEM S, 122(8), 2000, pp. 1762-1775
As a method to generate all-carbon molecules having highly reactive polyyne
units from stable precursors, the [2 + 2] cycloreversion of [4.3.2]propell
a-1,3,11-triene derivatives was developed, To test the efficiency of this m
ethod, the reaction was first applied to simple diethynyl- and dibutadiynyl
-substituted propellatrienes, which produced upon UV-irradiation linear hex
atriyne and decapentayne derivatives, respectively. Next, dehydro[12]-, [16
]-, [18]-, [20]-, and [24]annulene derivatives annelated by the [4.3.2]prop
ellatriene units were prepared as precursors to the corresponding cyclo[n]c
arbons, a monocyclic form of carbon clusters. Laser-desorption mass spectra
of the dehydroannulenes exhibited, in the negative mode, peaks due to the
corresponding cyclo[n]carbon anions (n = 12, 16, 18, 20, and 24) formed by
successive losses of aromatic indane fragments. Solution photolysis of the
dehydro[16]annulene and dehydro[18]annulene derivatives formed reactive pol
yyne intermediates by [2 + 2] cycloreversion which were intercepted by fura
n to give the corresponding Diels-Alder adducts. The structures and spectro
scopic properties of the dehydroannulenes annelated by the [4.3.2]propellat
riene units, the precursors to cyclo[n]carbons, and those annelated by the
oxanorbornadiene units, the products of the photolysis in furan, are discus
sed.