TOTAL SYNTHESES OF CARAZOSTATIN, HYELLAZOLE, AND CARBAZOQUINOCINS B-F

Total syntheses of carazostatin (1), hyellazole (2a), and carbazoquino cins B-F (3b-f) have been completed. The cross-coupling reaction betwe en 3-iodoindole 8 and vinylstannane 11b gave the 3-alkenylindole 7. Tr eatment of 7 with ethynylmagnesium bromide, followed by etherification of the resulting alcohol 12 with MOMCl, yielded the 3-alkenyl-2-propa rgylindole 6. The compound 6 was treated with t-BuOK in t-BuOH at 90 d egrees C to obtain the desired carbazoles 4 together with the N-deprot ected carbazole 13 through an allene-mediated electrocyclic reaction. The carbazole 13a, derived from 4a or 4c, was converted into the trifl ate 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 b y O-methylation gave hyellazole (2a). Oxidation of carazostatin (1) wi th benzene seleninic anhydride afforded carbazoquinocin C (3c). In a s imilar way, carbazoquinocins B and D-F (3b, d-f) were synthesized, res pectively.