Novel syntheses of murrayaquinone A and furostifoline through 4-oxygenatedcarbazoles by allene-mediated electrocyclic reactions starting from 2-chloroindole-3-carbaldehyde

The formal total synthesis of murrayaquinone A (1) and the total synthesis of furostifoline (5) were completed by the construction of 4-oxygenated 3-m ethylcarbazoles 7 based on a new type of electrocyclic reaction through 2-a lkenyl-3-allenylindole intermediates 8 derived from the 2-alkenyl-3-proparg ylindoles 9, starting from 2-chloroindole-3-carbaldehyde (11). The N,O-bisb enzyloxymethyl group of 16c and 22 underwent a Birch reduction followed by treatment with Triton B to produce the known 4-hydroxy-3-methylcarbazole (7 a) and 4-hydroxy-3-methylfuro[3,2-a]carbazole (7b) as precursors of murraya quinone A (1) and furostifoline (5), respectively, The trifluoromethanesulf onyloxy-3-methylfuro[3,2-a]carbazole (24), prepared from 7b, was subjected to reductive cleavage to provide furostifoline (5).