title: Total Syntheses of Carazostatin, Hyellazole, and Carbazoquinocins B-F.
abstract: Total syntheses of carazostatin (1), hyellazole (2a), and carbazoquinocins B-F (3b-f) have been completed. The cross-coupling reaction between 3-iodoindole 8 and vinylstannane 11b gave the 3-alkenylindole 7. Treatment of 7 with ethynylmagnesium bromide, followed by etherification of the resulting alcohol 12 with MOMCl, yielded the 3-alkenyl-2-propargylindole 6. The compound 6 was treated with t-BuOK in t-BuOH at 90 degrees C to obtain the desired carbazoles 4 together with the N-deprotected carbazole 13 through an allene-mediated electrocyclic reaction. The carbazole 13a, derived from 4a or 4c, was converted into the triflate 24 in two steps. The triflate 24 was subjected to the Suzuki cross-coupling reaction with either 9-heptyl-9-BBN or phenylboronic acid in the presence of a palladium catalyst to produce the 1-heptylcarbazole 25a and the 1-phenylcarbazole 25b. Cleavage of the ether bond of 25a yielded carazostatin (1). Cleavage of the ether bond of 25b followed by O-methylation gave hyellazole (2a). Oxidation of carazostatin (1) with benzene seleninic anhydride afforded carbazoquinocin C (3c). In a similar way, carbazoquinocins B and D-F (3b,d-f) were synthesized, respectively.
authors.affiliation: Faculty of Pharmacy and Pharmaceutical Sciences, Fukuyama University, Fukuyama, Hiroshima 729-02, Japan.
authors.forename: Tominari
authors.initials: T
authors.lastname: Choshi
authors.forename: Takuya
authors.initials: T
authors.lastname: Sada
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Fujimoto
authors.forename: Chizu
authors.initials: C
authors.lastname: Nagayama
authors.forename: Eiichi
authors.initials: E
authors.lastname: Sugino
authors.forename: Satoshi
authors.initials: S
authors.lastname: Hibino