The reaction of some indoles with acetic‐formic anhydride

Bis- and Trisindolylmethanes (BIMs and TIMs)

“…430 Indole in acetic-trifluoroacetic anhydride in ether at 20 °C gave crystals of BIM 204 in modest yield (Scheme 75). 431 The mechanism for this reaction is not straightforward, but it appears that the same type of mechanism for indole addition to a double bond occurs. The C-N bond in the indole that is attacked is destabilized by formation of the amide, while a new double bond is formed upon cleavage of the C-N bond.…”

“…As such, orthoformates were widely used with indoles in the presence of a catalyst such as AcOH, 570,571 PTSA, 572 H 2 SO 4 , 264,476 5-sulfosalicylic acid, 573 clay K-10, 574 or I 2 (Scheme 127). 575 TIMs are also obtained from the reaction of indoles and acetic-formic anhydride 413 431 or diethoxycarbenium salts 414 355,576 and diethyl carbonate (Figure 22). 577 Slice and Stanovnik synthesized tris(2-methyl-1-H-indol-3-yl)methane 416 via addition of 2-methylindole to com-pound 415.…”

“…Indole in acetic-trifluoroacetic anhydride in ether at 20 °C gave crystals of BIM 204 in modest yield (Scheme ) . The mechanism for this reaction is not straightforward, but it appears that the same type of mechanism for indole addition to a double bond occurs.…”

Access to Tetrasubstituted Tri(indolyl)methanes through Copper-Catalyzed Addition/Substitution Sequence

“…[4] As a consequence, development of new and practical methods to access tri(indolyl)methanes is of great significance. To this end, some related synthetic methodologies have been well established, mainly involving the cascade reactions of indoles with active carbonyls or their surrogates, such as orthoformates, [5] acetic-formic anhydride, [6] N,N-dimethylformaide dimethyl acetal, [7] 3-formylindole [8] and in situ generated 3-formylindole from indolylglycine [9] . Although these elegant cascade methodologies have the merits of operation simplification and step-economy, they often suffered from one or more intrinsic shortcomings, including the use of costly reagents, requirement of hazardous or corrosive promoters and limited substrate scope, etc.…”

NH4Cl-Promoted Synthesis of Symmetrical and Unsymmetrical Triindolylmethanes Under Solvent-Free Conditions

“…The formation of triindolylmethane from indole and ethyl orthoformate in the presence of ethanolic HCl first appeared in the literature in 1952. 6 Bergman 7 has reported the synthesis of TRIMs by using substituted indoles and acetic formic anhydride. The preparation of symmetrical TRIMs by the condensation of indoles with orthoformate in presence of p-TSA was reported by Akgün et al 8 Chakraborty and coworkers 9 have proposed a useful variation of this reaction using acid-washed montmorillonite clay as catalyst.…”