The selective oxidation of thiols to disulfides and sulfides to sulfoxides using graphite oxide (GO), a heterogeneous carbocatalyst obtained from low cost, commercial starting materials is described. The aforementioned oxidation reactions were found to proceed rapidly (as short as 10 min in some cases) and in good yield (51-100%) (19 examples). No over-oxidation of the substrates was observed, and GO's heterogeneous nature facilitated isolation and purification of the target products.
Graphite oxide (GO) was found to function as an auto-tandem oxidation-hydration-aldol coupling catalyst for the formation of chalcones in a single reaction vessel. Various alkynes or alcohols were hydrated or oxidized in situ to their corresponding methyl ketones or aldehydes, respectively, which underwent a subsequent Claisen-Schmidt condensation. Each of the aforementioned reactions proceeded in the absence of metals (confirmed by inductively coupled plasma mass spectrometry, ICP-MS) and afforded a range of chalcone products in good to excellent yields from commercially available starting materials.Keywords: chalcones; Claisen-Schmidt condensation; graphite oxide; heterogeneous catalysis; hydration; oxidation Building on the recent discovery that graphite oxide [1] (GO) -a carbon-based material rich with oxygencontaining functional groups -and graphene oxide (its exfoliated counterpart) effectively facilitate the oxidation of alcohols and hydration of alkynes, [2] we describe herein new methods for harnessing such broad reactivity to synthesize chalcones. As a motif commonly found in many natural products and often used as precursors in the preparation of flavonoids and isoflavonoids, [3] chalcones are typically prepared via the Claisen-Schmidt coupling of methyl ketones and aldehydes. However, recent efforts have focused on combining multiple transition metal-based catalysts to expedite the synthesis of new derivatives, particularly by expanding the range of amenable starting materials.
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