p-Toluenesulfonic acid → Dipyrromethane

Participants

Reaction Steps

As illustrated in Reaction Scheme 2, Step 1, an equimolar amount or a slight excess of a 2-(2-cyano 2-ethoxycarbonyl-ethen-1-yl)pyrrole derivative, shown as a compound of formula 201, is reacted with a 2-acetoxymethyl-5-benzyloxycarbonylpyrrole derivative of formula 202 in an organic solvent, preferably toluene, in the presence of a catalytic amount of p-toluenesulfonic acid to give the dipyrromethane of formula 203. The benzyl protecting group of the dipyrromethane 203 is then removed by palladium-catalyzed hydrogenation, as shown in Step 2, to give the corresponding dipyrromethane-2-carboxylate derivative of formula 204. As shown in Step 3, compound 204 is then decarboxylated in the presence of trifluoroacetic acid (“TFA”) to form the unstable dipyrromethane of formula 205. This compound is then reacted in situ (Step 4) with ah excess amount of a 2-chloromethyl-5-(2-cyano 2-ethoxycarbonyl-ethen-1-yl)pyrrole of formula 206, in an organic solvent in the presence of a catalytic amount of tin(IV) chloride, to form the non-symmetric tripyrrane of formula 207. The ethylcyanoacrylate groups are then cleaved with alkali to give the non-symmetric tripyrrane α,α′-dialdehyde of Formula I.

Provenance & Evidence