Tuning of Vinylborane Dienophilicity. Optimization of Reactivity, Regioselectivity, endo-Stereoselectivity, and Reagent Stability
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Simple syntheses of some vinylboranes are reported, and their properties in Diels-Alder reactions are compared. Vinyl-3,6-dimethylborepane was the most stable simple vinylborane examined, and appears to be indefinitely stable at 25°C. Surprisingly, trivinylborane is the most reactive, and reacts about 18 times faster than the vinyldialkylboranes with cyclopentadiene. Vinyl-9-BBN is the most regioselective dienophile, in keeping with principally steric control of regioselectivity in Diels-Alder reactions of vinylboranes. All the dienophiles display high endo-stereoselectivity with piperylene, but vinyl-3,6-dimethylborepane displays significantly improved stereoselectivity with cyclopentadiene. In general, by choice of alkyl-substituents on boron, the reactivity, regioselectivity, endo-stereoselectivity, and stability of vinylboranes can be optimized. © 1992.
author list (cited authors)
Singleton, D. A., Martinez, J. P., Watson, J. V., & Ndip, G. M.