Abstract
Dimethyl (β-substituted) vinylphosphonates do not readily undergo cross metathesis reactions with Grubbs catalyst and terminal alkenes. However, the corresponding mono- or diallyl vinylphosphonate esters undergo facile cross metathesis reactions. The improved reactivity is attributed to a relay step in the cross metathesis reaction mechanism.
Highlights
Over the last two decades, we have developed reactions for the formation of chiral non-racemic γ-substituted vinylphosphonates [1,2,3,4,5,6,7,8,9]
We recently described a method for the formal synthesis of centrolobine (8) [9], an antileishmananial compound isolated from the heartwood of various Centrolobium species [12,13,14,15,16] (Scheme 2)
When vinylphosphonate 12a was subjected to a cross metathesis reaction with methyl acrylate, the cross metathesis product 16a was formed in low yield
Summary
Over the last two decades, we have developed reactions for the formation of chiral non-racemic γ-substituted vinylphosphonates [1,2,3,4,5,6,7,8,9]. A solution of the vinylphosphonate 12b, 1.1 equivalents of allyl bromide and 5 mol % TBAI in toluene was heated at reflux for 7 hours to give a 53% conversion to both the mono- and diallyl vinylphosphonates 14a and 14b in a 10:1 ratio. A subsequent reaction of vinylphosphonate 12b employing 5 equivalents of allyl bromide, 5 mol % TBAI and 18 hours at reflux resulted in 87% conversion with 1.2:1 ratio of mono- to diallyl ester (14a and 14b). THF-substituted vinylphosphonate 19 was treated with 5 equivalents of allyl bromide and 5 mol % TBAI in refluxing toluene for 36 hours to give a 76% conversion with 1.8:1 ratio of mono- to diallylated vinyl phosphonates 20a and
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