Polystyrene PHB (Wang resin)

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/DCM 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. Solid-phase lactam syntheses were also achieved by reaction of the resin-bound isonitrile with an amine and an ω-keto-acid as well as other synthetic transformations such as the Biginelli reaction and construction of heterocycles such as quinolones, imidazoles, hydantoins, and 1,4-benzodiazepine-2,5-diones.