Dialkylboron trifluoromethanesulfonates

Boron enolates can be prepared by reaction of the ketone with a dialkylboron trifluoromethanesulfonate (triflate) and a tertiary amine.16 Use of boron triflates and a bulky amine favors the Z-enolate. The resulting aldol products are predominantly the syn stereoisomers. 

Dialkylboron trifluoromethanesulfonates (Inflates) are particularly useful reagents for the preparation of boron enolates from carbonyl compounds, including ketones, thioesters and acyloxazoiidinones. Recentiy, the combination of dicylohexyiboron trifluoromethanesulfonate and triethyiamine was found to effect the enolization of carboxyiic esters. The boron-mediated asymmetric aldoi reaction of carboxyiic esters is particuiariy usefui for the construction of anti p-hydroxy-a-melhyl carbonyl units. The present procedure is a siight modification of that reported by Brown, et ai. ... 

In the case of cyclohexanone the cyclopentylthexyl boron enolate must be employed to achieve high diastereoselectivity. See also Dialkylboron trifluoromethanesulfonates, this volume. 

Dialkylboron trifluoromethanesulfonates, RaBOTf. These triflates are prepared by reaction of trialkylboranes with triflic anhydride. 

Excellent results have been obtained by using boron enolates (alkenyloxyboranes or enol borinates), in what is commonly known as a boron-mediated aldol reaction. The boron enolates are prepared easily from the corresponding ketone and a dialkylboron trifluoromethanesulfonate (dialkylboron triflate, R2BOTf) or chloride (R2BCI) and a tertiary amine base. Boron enolates react readily with aldehydes to give, after oxidative work-up of the resulting borinate species, high yields of the desired aldol product (1.58). 

ALDOL CONDENSATION Cesium fluoride. Dialkylboron trifluoromethane-sulfonates. Dichlorobis(cyclopentadi-enyl)zirconium. Diisobutylaluminum phenoxide. 2,5-Dimethylphenylpropi-onate. DimetIiyl(phenyllhio)aIuminum. Lithium iodide. Triethylborane. Tri-methylsilyl trifluoromethanesulfonate. Triphenyltin chloride. TrisCdiethyI-amino)sulfonium difluorotrimethyl-siliconate. 

ALDOL CONDENSATION (+)-(R)-l-Amino-2- methoxymethyl)pyrrolidine. Boron trichloride. Dialkylboron tri-fluoromethanesulfonates. Dibenzyl-ammonium trifluoroacetate. Di- -butylboryl trifluoromethanesulfonate. Dichlorodiethylaminoborane. Diiso-propylaluminum phenoxide. Diisopropyl-aminomagnesium bromide. Lithium diisopropylamide. Morpholine-Camphoric acid. Proline. 

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