Two‐Step Access toβ‐Substitutedo‐Hydroxyphenyl Ethyl Ketones from 4‐Chromanone and its Application in Preparation of a Silica‐Supported Cobalt(II) Salen Complex

Abstract

The o‐hydroxyphenyl ethyl ketone skeleton is prevalent in many biologically active natural products and active pharmaceutical ingredients. Herein, a two‐step protocol has been developed for synthesis of various β‐substituted o‐hydroxyphenyl ethyl ketones. A base‐mediated ring opening of 4‐chromanone was used to introduce the β‐ethoxyl o‐hydroxyphenyl ethyl ketone intermediary, followed by nucleophile substitution under BF3 ⋅ Et2O assisted conditions to give the desired β‐carbon, nitrogen, or thiol substituted o‐hydroxyphenyl ethyl ketones. With the aid of this protocol, a silica‐supported cobalt(II) salen complex was successfully prepared and its structure was confirmed by FTIR, 13C MAS NMR, UV‐Vis absorption, and XPS spectra. The immobilized cobalt(II) salen catalyst not only displayed comparable catalytic activity in the synthesis of several heterocycles including 1,3‐oxazolidine, benzimidazole, and benzoxazole as compared with their homogeneous counterparts, but also could be recycled for several times without obvious loss of its catalytic activity.