| Popis: |
The canthine derivative 1b was synthesized efficiently by treatment of N a -(4,4-diethoxybutyl)-N b -allyloxytryptamine 9b with TFA/H 2 O in chloroform. This result demonstrates that PS cyclization can indeed occur by direct attack of the indole 2-position at the intermediate iminium ion under mild conditions. With N a -propanal chains, only dimeric and oligomeric compounds were isolated. With the N a -pentanal chain (unidentified) oligomeric compounds were formed as well. The monomeric canthine-like products have not been detected in these cases, probably because formation has to proceed via conformationally disfavored intermediate cyclic iminium ions. Cyclization of N a -butanal functionalized N b -formyl- or N b -benzyltryptamines 9c and 9d , which are known rate enhancing substituents in the PS condensation, unexpectedly gave the 3,4-dihydro pyrimidino[1,2- a ]indoles 16c,d in high yields. The products 16c,d were formed by a direct electrophilic attack of the protonated aldehydes on the indole 2-position. |
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