Bis-2-hydroxy-3-methylcarbazole

Scheme 25 Synthesis of the 2-oxygenated tricyclic carbazole alkaloids 66-69 and l,r-bis(2-hydroxy-3-methylcarbazole) 70...

Scheme 2.11) indicating a similar carbazole unit. The EI-MS spectrum showed a molecular ion peak at m/z 392, and a peak at m/z 196, suggesting a symmetrical dimeric carbazole with two, 2-hydroxy-3-methylcarbazole units. The H-NMR spectrum was also similar to that of 2-hydroxy-3-methylcarbazole (52), except for the lack of the signal for H-1 (H-1 ), indicating a C-1/C-T-linkage between the two 2-hydroxy-3-methylcarbazole units. Based on the spectroscopic data and additional support by NOE experiments, structure 213 was assigned to bis-2-hydroxy-3-methylcarbazole (82). 

Similarly, 1-hydroxy-3-methylcarbazole (23) and 2-hydroxy-3-methylcarbazole (52) could lead to bis(0-demethylmurrayafoline A) (204) and bis-2-hydroxy-3-methylcarbazole [l,l-bis(2-hydroxy-3-methylcarbazole)] (213), respectively, as shown in Scheme 3.9. Although bis(0-demethylmurrayafoline A) (204) is a non-natural carbazole derivative, the isolation of 2-hydroxy-3-methylcarbazole (52) and bis-2-hydroxy-3-methylcarbazole [l,l-bis(2-hydroxy-3-methylcarbazole)] (213) from M. komigii supports the oxidative dimerization of 2-hydroxy-3-methylcarbazole (52) (Scheme 3.9). 

We reported the first total synthesis of l,T-bis(2-hydroxy-3-methylcarbazole) (213) using our molybdenum-mediated construction of the carbazole framework (560). The required monomer, 2-hydroxy-3-methylcarbazole (52), was obtained in three steps, and 22% overall yield, starting from dicarbonyl(ri -cyclohexa-l,3-diene)(ri -cyclopentadienyl)molybdenum hexafluorophosphate (663) and 3-meth-oxy-4-methylaniline (655) (560) (see Scheme 5.52). Finally, oxidative coupling of the monomer 52 using p-chloranil afforded l,T-bis(2-hydroxy-3-methylcarbazole) (213) in 38% yield (560) (Scheme 5.167). 

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