Polystyrene A PHB

The Wang support is the most widely used resin for attaching carboxylic acids for further functionalisation. Cleavage conditions for the ester anchor involve concentrated TFA or TFA/CH₂CI₂ mixtures to provide carboxylic acids or cyclization-cleavage under acidic or basic conditions. Release of an amide function by treatment with an amine in the presence of a Lewis acid was also reported. Wang resin was used to add vinyl and iodobenzoic acids via carbodiimide coupling and the products subjected to Heck conditions with alkenes or with alkynes or to Suzuki coupling with boron reagents. The Ugi multicomponent condensation reaction was conducted on Wang resin with the carboxylic acid, amine or isonitrile as the anchored functional group. On a Wang resin primary, secondary, and tertiary alcohols have been converted to 4-methoxy-benzyl ethers. As well as anchoring carboxylic acids to this resin, phenols were attached under Mitsunobu conditions, subjected to further transformations and cleaved under acidic conditions.These resins are alternatives to the traditional Wang resins and ideal for the attachment of carboxylic acids by esterification. The phenethyl ether bond is more stable than the benzyl ether bond towards acid treatments.