Heterocyclic polymer catalyzed synthesis

Abstract An overview on the microwave-enhanced synthesis and decoration of the 2(lH)-pyrazinone system is presented. Scaffold decoration using microwave-enhanced transition-metal-catalyzed reactions for generating structural diversity, as well as the conversion of the 2(lH)-pyrazinone skeleton applying Diels-Alder reactions to generate novel heterocyclic moieties are discussed. The transfer of the solution phase to polymer-supported chemistry (SPOS) is also described in detail. 

The synthesis of poly(vinyl acetals) (252) represents another example of generating a heterocycle, in this case the 1,3-dioxane nucleus, by application of a polymer modification reaction. Generally, the polymer modified is poly(vinyl alcohol) (180) or one of its copolymers. The 1,3-dioxane ring is generated (Scheme 122) by an acid-catalyzed acetalization reaction with an aldehyde, although ketones have also been reacted. A review (71MI11102) is available covering synthesis, properties and applications of the two most common and industrially important poly(vinyl acetals), poly(vinyl butyral) and poly(vinyl formal), as well as many other functional aldehydes that have been attached. 

Generation of a diene from a polymer-bound benzocyclobutane [320] The polymer-bound benzocyclobutene (358) can be converted into a very reactive diene upon thermal 47r-conrotatory ring opening. The resulting diene (359) can react with a series of dienophiles containing heteroatoms to afford a series of heterocycles (Scheme 75). Lewis acid-catalyzed reductive alkylation concluded the synthesis to give 363. 

The synthesis of chiral poly(depsipeptides), polymers with alternating amide and ester bonds, by lipase-catalyzed ring opening of 3-isopropyl morpholino-2,5-dione (19) was shown by Hocker and coworkers (Scheme 11.5) [26], Various lipases were tested for the bulk polymerization of these heterocyclic monomers at temperatures of 100 °C or above. PPL and lipase type III from a pseudomonas species were shown to be effective catalysts. The isolated polymers showed Mn values of 3.5-17.5 kgmol-1. The influence of reaction temperature, the amount of enzyme and the presence of water in the reaction medium were shown to be important factors on the high molecular weight fraction and were investigated in detail [26b]. Comparison of optical rotation values for polymers prepared by... 

Ni(0)-catalyzed polymerization by the Colon or Yamamoto procedure seems to be an easy and economically feasible synthetic route to a wide range of heterocyclic and phenyl-based polymers. High molecular weights are obtained and the past five years have been rich in the synthesis of new materials and PPP subunits. Nevertheless, side-groups such as halides, acids, alcohols, primary and secondary amines and nitro groups may interfere with the reaction and should be avoided or introduced in protected forms. 

Arylyne cyclization is an important reaction affording the formation of carbocycles in the synthesis of complex molecules. CT-Bonded metal salt polymer or organic moiety linked to the inorganic support, silaphenylmercuiic triflate, showed efficient catalytic activity for a variety of mercury(ll) trifluoromethanesulfonate [Hg(OTf)J-catalyzed reactions [104,132-134]. Examples described by Equations (8.36)-(8.43) present cyclo- and cycloisometization reactions leading to the synthesis of both carbocycles and heterocycles. 

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