A Homo-Proline Tetrazole as an Improved Organocatalyst for the Asymmetric Michael Addition of Carbonyl Compounds to Nitro-Olefins

Abstract

A new homo-proline tetrazole derivative 7 has been prepared and shown to have improved properties for achieving asymmetric Michael addition of carbonyl compounds to nitro-olefins.

asymmetric - nitro-Michael - organocatalysis - homo-proline - tetrazole

References

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<A NAME="RD38604ST-9">9</A>

Typical Experimental Procedure.
To a suspension of catalyst (15 mol%) and nitro-olefin (0.5 mmol) in an i-PrOH-EtOH mix (1:1, 2 mL) was added ketone (0.75 mmol, 1.5 equiv) and the resulting mixture stirred at 20 °C for 24 h. After this time the reaction was quenched with sat. NH₄Cl (2 × 20 mL) and the aqueous phase extracted with EtOAc (2 × 25 mL). The combined organic layers were dried (MgSO₄), filtered and evaporated to give a residue which was further purified by flash column chromatography using EtOAc and petroleum ether 40-60 as eluent.

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<A NAME="RD38604ST-12">12</A>

This was proven by comparison of chiral HPLC retention times and also by an inversion of sign in the optical rotation as compared to literature.