Propylene Oxide Assisted Sonogashira Coupling Reaction

Abstract

A propylene oxide assisted base-free Sonogashira cross-coupling reaction has been developed. The unique feature of the current protocol has extended the scope of Sonogashira reaction to some base-sensitive substrates.

base-free - propylene oxide - Sonogashira reaction

References and Notes

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4 To the best of our knowledge, PO has not been used in C-C bond formation. For the sole relevant precedent (in C-S bond formation), see: Moreau X. Campagne J.-M.
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5a For an example of Sonogashira reaction with Et₃N as both the solvent and the base in preparing diphenylacetylene, see: Perner RJ. Gu Y.-G. Lee C.-H. Bayburt EK. McKie J. Alexander KM. Kohlhaas KL. Wismer CT. Mikusa J. Jarvis MF. Kowaluk EA. Bhagwat SS. J. Med. Chem.  2003,  46:  5249 

5b

General Procedure: The Batey Pd-carbene complex 1 (2.5 mol%), CuI (5 mol%), Ph₃P (2.5 mol%) and DMF (2 mL) were added to a dry 10-mL septum-capped round-bottomed flask under a nitrogen atmosphere. Aryl iodide (2 mmol), alkyne (110 mol%), and PO (5 equiv) were then added to the above mixture. While the mixture was stirred, the flask was cooled to -78 ˚C, vacuumed, and charged with nitrogen. This process was repeated for three times. After the mixture was warmed to 25 ˚C, stirring was continued at that temperature for 48 h. The mixture was diluted with H₂O and extracted with E₂O. The organic extracts were combined, washed with brine, dried (MgSO₄), filtered, and concentrated to give a residue, which was purified by flash column chromatography on silica gel.

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