Stereoselective synthesis of C-fused pyranoindoles, pyranobenzofurans and pyranobenzothiophene scaffolds using oxa-Pictet–Spengler type reaction of vinylogous carbonates

Abstract

C-fused pyranoheterocycles can be readily assembled using an intramolecular oxa-Pictet-Spengler type reaction of vinylogous carbonates in a highly stereoselective manner. Required indole and benzofuran rings tethered to vinylogous carbonates are prepared by a tandem Sonogashira coupling-nucleopalladation reaction. The entire process can also be carried out in a 'one-pot' manner starting from homopropargyl alcohol. The C-fused pyranoindoles could be converted to spirooxindoles as well as to ring expanded products under oxidative conditions.

Synthesis of 2,9-dihydropyrano[2,3-b]-indoles via intramolecular oxa-6π-electrocyclization reaction from synthesized 3-allylideneindolin-2-one intermediates

“…All chemicals were used and purchased from Sigma-Aldrich without puri cation unless otherwise commented. The products were characterized by NMR data that were acquired for 1 H at 500 MHz and for 13 Then, 0.6 mL solution of NH4Cl were added drop by drop to the mixture within 1-2 min. After that, 0.1 mmol Zn powder was added and stirred for 3 h. The progress of reaction was monitored by Thin Layer Chromatography (TLC) using n-hexane/ethyl acetate (1:5) as eluent.…”

A Comprehensive Review on Pyranoindole-containing Agents

“…Gharpure and Prasath explored the oxa-Pictet-Spengler type reaction of vinylogous carbonates for the stereoselective synthesis of tetrahydropyrano [3,4b]indoles (series 4) [77]. Xie et al reported the Rh(II)catalyzed intramolecular annulation of N-sulfonyl-1,2,3-triazoles towards the highly stereoselective synthesis of series 4 pyranoindoles (Scheme 13) [78].…”

(3 + 3) Annulation of acetoxy allenoates with enolisable carbonyl substrates leading to fused pyrans

“…Among the products, pyrano-pyrazole 12 and indolo-pyran frameworks 13 show a wide variety of pharmaceutical activities; some important scaffolds with the pyrano-benzofuran moiety 14 are also known. Selected examples of pharmaceutically relevant fused-pyrans are depicted in Fig.…”