Oxazoline Cyanocuprate: A New Approach to β-Carboxymethyl Functionalization of Enones

Abstract

This paper describes the preparation of a series of oxazoline cuprates by reaction of an oxazoline lithium anion with copper(I) salts: CuBr˙DMS, CuI and CuCN in THF solution. The oxazoline cyanocuprate showed the best reactivity using enones as electrophiles.

cuprate - Michael addition - enones - 2-oxazolines - δ-keto-oxazolines

References

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General Procedure for the Preparation of Oxazoline Cyanocuprate ( 1f): To a solution of 2,4,4-trimethyl-2-oxazoline (0.452 g, 4 mmol) in THF (8 mL) at -78 ºC was added n-BuLi in hexanes (1.8 mL, 4.2 mmol). After stirring for 30 min at -78 ºC, a solution of CuCN˙2LiCl (0.348 g, 2 mmol, LiCl was dried in an oil bath heating (180 ºC) under 0.05 mmHg vacuum during 3 h immediately before use) , at -78 ºC in THF (2 mL) was added to the oxazoline anion and the resulting solution was stirred at -78 ºC for an additional 30 min, yielding a reddish-brown solution. The solution of enone (2 mmol) in dry THF was slowly added and stirred for 2 h at -78 ºC. The reaction mixture was quenched with MeOH (0.5 mL) and a 10% NH₄OH solution in a sat. NH₄Cl solution (3 mL). The mixture was extracted with Et₂O (10 mL), the phases were separated and the aqueous phase was extracted with Et₂O (3 × 5 mL). The combined organic extracts were washed with sat. NaCl solution (1 × 5 mL) and dried over MgSO₄. The filtrate was concentrated under reduced pressure and the crude product was purified by flash chromatography.

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