Preparation of Functional Benzofurans, Benzothiophenes, and Indoles Using Ester, Thioester, and Amide via Intramolecular Wittig Reactions

Abstract

Preparation of new types of highly functional benzofurans, benzothiophenes, and indoles is realized via intramolecular Wittig reactions with the corresponding ester, thioester, and amide functionalities. The key intermediates, phosphorus ylides, presumably result from the addition of Bu(3)P toward aldehydes followed by acylation and deprotonation. Synthesis of functional benzofurans directly starting from salicylic aldehyde derivatives with acid chlorides in a one-step procedure is also developed.

Bench‐Stable Electrophilic Indole and Pyrrole Reagents: Serendipitous Discovery and Use in C–H Functionalization

“…However, extensive NMR analysis performed on the product obtained from indole 14 were not in agreement with this assignment, and fitted better with structure 17 still containing a hypervalent iodine atom ( Figure ). First, the expected proton and carbon chemical shifts around the iodine atom were estimated for both envisaged structure 15 and 17 based on the reported values for 1‐(1,1,1,3,3,3‐hexafluoro‐2‐methoxypropan‐2‐yl)‐2‐iodobenzene, indoles bearing an oxygen substituent on the C(3) position, [ ][ ] hexafluoroisopropanol‐derived hypervalent iodine reagents and indole iodonium salts . The observed indole C(2) 1 H signal at 7.51 ppm is in lower field than expected for a compound such as 15 , but this fact alone was not sufficient to support the hypervalent structure.…”

Aerobic C–C Bond Cleavage of Indoles by Visible‐Light Photoredox Catalysis with Ru(bpy)32+

“…N ‐(2‐Formylphenyl)‐ N ‐methylbenzamide (2w): Colorless oil (54.5 mg, 76 % yield). 1 H NMR (400 MHz, CDCl 3 ): δ = 10.10 (s, 1.0 H), 7.73 (d, J = 6.8 Hz, 1.0 H), 7.52 (t, J = 6.6 Hz, 1.0 H), 7.34 (t, J = 6.6 Hz, 1.0 H), 7.20–7.10 (m, 6.0 H), 3.50 (s, 3.0 H) ppm.…”

Last Decade of Unconventional Methodologies for the Synthesis of Substituted Benzofurans

“…The key phosphorus ylide intermediate presumably resulted from the addition of Bu 3 P toward salicylaldehydes followed by acylation and deprotonation. The umpolung reactivity of carbonyl carbon of the aldehyde allowed the synthesis of functional benzofurans [125] (Scheme 38).…”