Indole-3-carboxylic acid, 1-methoxy reactions

Beccalli et al. reported a synthesis of carbazomycin B (261) by a Diels-Alder cycloaddition using the 3-vinylindole 831 as diene, analogous to Pindur s synthesis of 4-deoxycarbazomycin B (619). The required 3-vinylindole, (Z)-ethyl 3-[(l-ethoxy-carbonyloxy-2-methoxy)ethenyl]-2-(ethoxy-carbonyloxy)indole-l-carboxylate (831), was synthesized starting from indol-2(3H)one (830) (620). The Diels-Alder reaction of the diene 831 with dimethyl acetylene dicarboxylate (DMAD) (535) gave the tetrasubstituted carbazole 832. Compound 832 was transformed to the acid 833 by alkaline hydrolysis. Finally, reduction of 833 with Red-Al afforded carbazomycin B (261) (621) (Scheme 5.99). 

Cyclization of the anilide 213 using TiCU produced the 3-chloro-substituted oxindole 214 (Equation 69), whereas a similar reaction induced by BF3-OEt2 gave the corresponding methoxy-substituted derivative <1998T4889>. Lewis acids have also been used in an approach to indole-2-carboxylates based on cyclization of (Z)-A(A -dimethyl-aminopropenoates derived by exposure of A -arylglycinates to DMEDMA <2006SL749>. 

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