Chemoselective Cascade Synthesis of N‐Fused Heterocycles via Silver(I) Triflate‐Catalyzed Friedel–Crafts/N‐C Bond Formation Sequence

Abstract

An efficient cascade methodology toward chemoselective synthesis of N-fused heterocycles in-indole derivatives has been developed. This transformation proceeds via a silver(I) triflate-catalyzed consecutive FriedelCrafts reaction/N À C bond formation sequence between readily available propargyl alcohols and 3-substituted 1H-indoles. Not only is excellent chemoselectivity observed according to the substitution patterns of propargyl alcohols, but also the Lewis acid-catalyzed N À C bond formation process can be carried out under base-and ligand-free conditions.

Synthesis and Some Biological Properties of Pyrrolo[1,2‐a]indoles

“…The interaction of N ‐acetyl indole manganate 118 with dimethyl acetylenedicarboxylate 101a or diphenylacetylene 119 resulted in the formation of pyrroindoles 120 and byproducts of simple demetalation 121 . Similar transformation in the presence of silver trifluoromethanesulfonate in nonpolar solvents such as petroleum ether and heptane was described in . The process is initiated from thermal or oxidating activation by trimethylamine oxide.…”

Synthesis and Applications of 9H‐Pyrrolo[1,2‐a]indole and 9H‐Pyrrolo[1,2‐a]indol‐9‐one Derivatives

“…In 2010, a new cascade silver(I) triflate‐catalyzed Friedel‐Crafts/N–C bond formation protocol was developed by Zhan et al for the synthesis of N‐fused heterocycles 101 (Scheme ) . This highly chemoselective transformation occurs between propargyl alcohols 99 and 3‐substituted 1 H ‐indoles 100 , with AgOTf as Lewis Acid.…”

“…In 2010, a new cascade silver(I) triflate-catalyzed Friedel-Crafts/N-C bond formation protocol was developed by Zhan et al for the synthesis of N-fused heterocycles 101 (Scheme 22). [36] This highly chemoselective transformation occurs between propargyl alcohols 99 and 3-substituted 1H-indoles 100, with AgOTf as Lewis Acid. Unlike to other additions of unprotected 1H-indoles to alkynes displayed in the literature, the present process was developed with base-and ligand-free conditions.…”

Transition Metal-Mediated Synthesis of Monocyclic Aromatic Heterocycles

“…In case of nonaromatic substituent at the acetylene 3-449 (R 3 = TMS or n- Bu), a complete isomerization to pyrrole did not occur, and N-fused indoles 3-452 were formed exlusively (Scheme 291). 450 …”