Michael reaction of indoles with 3-(2′-nitrovinyl)indole under solvent-free conditions and in solution. An efficient synthesis of 2,2-bis(indolyl)nitroethanes and studies on their reduction

An analytical perspective on favoured synthetic routes to the psychoactive tryptamines

“…When nitrovinylindole 28 was refluxed with N-acetyltryptamine 32 under similar conditions a dimeric compound 33 was obtained ( Fig. 3D) [39]. These findings suggest that formation of similar compounds as by-products cannot be completely excluded under similar reaction conditions.…”

“…(D) N-acetyltryptamine (32) was found to dimerise when refluxed with 28 under similar conditions. (E) A reduction of 2,2-bis(3 -indolyl)nitroethane 34 to its ethylamine counterpart 35[38,39].…”

Functionalization of Indole and Pyrrole Cores via Michael-Type Additions

“…Although all indoles gave the expected unsymmetrical bis(indolyl)nitroethanes, 1-acetylindole (235) Scheme 51 did not provide the expected product. Interestingly, 1-alkylindoles 14 and 228-230 furnished both the expected products (52-63%) and the symmetrical bis(indolyl)nitroethanes as minor products (20-27%) (Scheme 52) [174,177]. The formation mechanism for the unexpected symmetrical product 237 is shown in Scheme 51.…”

“…Recently, the use of 3-(2 -nitrovinyl)indole (227) as a Michael acceptor with indoles as nucleophile have been reported [174,177]. Michael reaction of 227 with eight 3-unsubstituted indoles (2, 14, 19, 228-235 silica gel, which acts as a mild acidic catalyst, under microwave irradiation or room temperature gave unsymmetrical bis(indolyl)nitroethanes (236a-h) in excellent yields (69-86%) (Scheme 51 and Table 6).…”

“…Furthermore, the symmetrical bis(indolyl)nitroethane 236a, as a model structure, could be reduced to the corresponding amine, isolated as its N-acetyl derivative 241 (Scheme 53) [174,177].…”