Generation and Characterization of Transient 3 H ‐Indolium‐methanides

Transient 3 H ‐indolium‐methanides 3a – d have been generated from the corresponding 2‐substituted 3 H ‐indoles 1a – d by the N ‐(trimethylsilyl)methylation/desilylation method. 3a,b were trapped by dimethyl maleate and dimethyl fumarate stereospecifically. All ylides add dimethyl ethynedicarboxylate to form 9,9a‐dihydro‐3 H ‐pyrrolo[1,2‐ a ]indoles 11a – d , out of which 11c,d (R = 9a‐alkoxy) readily eliminate the corresponding alkanols to form 12 . In the absence of dipolarophiles, 1a is predominantly transformed into Fischer base 14 , whereas 3b gives rise to an unsymmetrical dimer 16 .