What is it about?
The first “green” asymmetric organocatalytic reaction in a supercritical carbon dioxide medium has been elaborated. Under the proposed conditions (100 bar, 35oC), nitroolefins enantioselectively accept diphenylphosphite in the presence of bifunctional squaramide organocatalysts affording corresponding -nitrophosphonates in high yields and with enantioselectivities of up to 94% ee. Both enantiomers of the products are accessible by this methodology. A significant potential of the supercritical extraction for product isolation and catalyst recovery has been demonstrated.
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Why is it important?
In the developed procedure, the supercritical carbon dioxide serves not only as a prospective green medium for the asymmetric Michael reaction. It has a significant potential as a substitute of organic solvents, undesirable in terms of green chemistry, during workup. In particular, it is useful for isolation of the products by supercritical fractional extraction from the reaction mixture. Moreover, supercritical chromatography may be applied for their purification in reactions where reagents and products have similar solubility in supercritical carbon dioxide.
Perspectives
The obtained results contribute to Green Chemistry as they eliminate toxic organic solvents (in particular, CH2Cl2) originated from exhausting hydrocarbon resources and facilitate separation and purification steps that usually have the highest environmental impact in chemical processes. Furthermore, the availability and recyclability of CO2 and recoverability of precious chiral catalysts under proposed conditions along with anticipated reduction of production costs per product unit in the large-scale industrial processes would hopefully make sc-CO2-based catalytic technologies economically beneficial in spite of the need of using special equipment and additional energy costs.
Sergei Zlotin
N.D. Zelinsky Institute of Organic Chemistry RAS
Read the Original
This page is a summary of: Stereodivergent Michael addition of diphenylphosphite to α-nitroalkenes in the presence of squaramide-derived tertiary amines: an enantioselective organocatalytic reaction in supercritical carbon dioxide, Green Chemistry, January 2014, Royal Society of Chemistry,
DOI: 10.1039/c3gc41647j.
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