Major Effect of the Leaving Group in Dialkylboron Chlorides and Triflates in Controlling the Stereospecific Conversion of Ketones into Either (E)- or (Z)- Enol Borinatesxxb
PURDUE UNIV LAFAYETTE IN RICHARD B WETHERILL LAB
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The ready synthesis and ease of dialkylboron chlorides, R2BCI, compared to triflates, R2BOTf, give the chlorides a significant advantage as reagents to achieve the conversion of ketones into enol borinates, regiospecifically and quantitatively. This made possible the first study of the effect of changes in the leaving group on the ratios of E-Z-enol borinates produced. Indeed, a systematic study of the effect of the steric requirement of the R group R9BBN vsChx2, the amine Et3N vs i-Pr2EtN, and the leaving group CL vs OTf, with two representative ketones, propiophenone and diethyl ketone, revealed a controlled shift from preferential formation of the Z-enol borinates to the E-enol borinates. The technique was applied to other representative ketones and selective conversion to both E-enol borinates approx. 99 and Z- enol borinates approx. 80-99 and Z-enol borinates 97-99 has been achieved. Enol borinates are valuable intermediates in organic synthesis.
- Organic Chemistry