Mechanism and optimisation of the homoboroproline bifunctional catalytic asymmetric aldol reaction: Lewis acid tuning through in situ esterification.
The use of homoboroproline as a bifunctional catalyst in the asymmetric aldol reaction has been investigated mechanistically, particularly with respect to tuning the Lewis acidity of boron by in situ esterification with mildly sigma-electron withdrawing diols such as hydrobenzoin and tartrate esters. The stability of simple cyclohexyl and cyclopentyl boronate diol esters shows that the 5-ring boronate esters are more stable, which sheds light on the mode of action of esterified homoboroproline catalyst in the enamine-mediated aldol reaction, which is also studied by NMR. The result is reaction optimisation to provide an efficient aldol reaction and a proposed mechanistic proposal.
Centre for Sustainable Chemical Processes, Department of Chemistry, Durham University, Science Laboratories, South Road, Durham DH1 3LE, UK.
Irene
I
Georgiou
Andrew
A
Whiting
D000447:Aldehydes / Q000737:chemistry; D002384:Catalysis; D004951:Esterification; D058116:Lewis Acids / Q000737:chemistry*; D015394:Molecular Structure; D011392:Proline / Q000031:analogs & derivatives* / Q000737:chemistry; D013237:Stereoisomerism
D000447:Aldehydes; D058116:Lewis Acids; C116609:3-hydroxybutanal; D011392:Proline; C010983:homoproline