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Metal‐free Hydroalkoxylation‐Formal [4+2] Cycloaddition Cascade for the Synthesis of Ketals
Author(s) -
Gharpure Santosh J.,
Nanda Santosh K.,
Shelke Yogesh G.
Publication year - 2017
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201701659
Subject(s) - salicylaldehyde , chemistry , cycloaddition , intramolecular force , stereoselectivity , oxonium ion , combinatorial chemistry , stereochemistry , catalysis , organic chemistry , ion , schiff base
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.