Petasis polymer-supported

Finn also showed the formation of 2H-chromenes under the same reaction conditions, using alkenylboronic acids and morpholine in dioxane at 90 °C. A more convenient route to the 2H-chromenes was then developed using a catalytic amount of dibenzylamine in the presence of alkenylboronic adds and salicylaldehyde (42, Scheme 7.11) [30]. Chromenes 43 were reported to arise from the initial Petasis borono-Mannich adducts 44 via an add promoted intramolecular S 2 attack of the ortho-hydroxyl group onto the protonated allylic amine of intermediate 45. A more likely mechanism involves elimination from 45 to intermediate 46, followed by 6n-electrocychzation to the product The reaction is tolerant of various functional groups and substitution patterns on the salicylaldehyde, and could also be promoted using a polymer-supported base, such as Merrifield resin-supported dibenzylamine (40-50 mol%) [30]. 

Polymer-supported Petasis Borono-Mannich Reactions... 

Scheme 7.13 Application of polymer-supported amines in the Petasis borono-Mannich reaction.

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