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Updated: Mar 2, 2026

A Two-Step Protocol for Umpolung Functionalization of Ketones Via Enolonium Species
Published on: August 16, 2018
Metal-free Hydroalkoxylation-Formal [4+2] Cycloaddition Cascade for the Synthesis of Ketals
Santosh J Gharpure1, Santosh K Nanda1, Padmaja1
1Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, 400076, India.
Abstract:
A transition metal free, acid promoted cascade hydroalkoxylation-formal [4+2] cycloaddition of various alkynols with salicylaldehyde is demonstrated for the synthesis of tetrahydrofurano/pyrano-chromenes and spiroketals. In general, alkynols underwent hydroalkoxylations in an endo-dig manner when internal alkynes were used to furnish the heteroannular ketals, whereas terminal alkynes proceeded in an exo-dig fashion leading to spiroketals. The study revealed that intramolecular hydroalkoxylation of alkynols is a preferred path over a generation of oxonium ions when coupling partner is salicylaldehyde. This metal-free transformation provides a new avenue for the stereoselective synthesis of tetrahydrofurano- and pyrano-chromenes in an expeditious manner.
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