Microwave assisted DIC-promoted intramolecular cyclization for solid phase synthesis of trisubstituted imidazolidinones and pyrimidinones

The preparation of (4H)-imidazol-4-ones and their application in the total synthesis of natural products

(4H)-Imidazol-4-ones are an important scaffold for a variety of applications, including natural products, medicine, agriculture, and other applications. Over the years, there have been a number of preparations published for the synthesis of imidazol-4-ones. This review discusses the progress made on the synthesis of imidazol-4-ones, and their application towards the total synthesis of a range of imidazol-4-one containing natural products. Emphasis is made on areas of the field that still need progress.

Advances in the Solid-Phase Synthesis of Pyrimidine Derivatives

This Review describes the existing synthetic approaches for the solid-phase synthesis (SPS) of differently substituted and fused pyrimidine derivatives. These synthetic strategies are classified on the basis of the different synthetic routes leading to the particular type of pyrimidine heterocycle formed. The Review discusses the application of a variety of polystyrene derived supports for the construction of pyrimidine rings. The effect of microwave heating on the solid-phase synthesis is also addressed in the review.

Facile synthesis of glycosylated Fmoc amino acid building blocks assisted by microwave irradiation

The synthesis of glycosylated Fmoc amino acids by reaction of mono- and disaccharide peracetates with Fmoc amino acids having free carboxyl groups was rapidly promoted by Lewis acids (SnCl(4), BF(3)·Et(2)O) under microwave irradiation. The products are useful building blocks for the synthesis of glycopeptides.

Soluble polymer-supported synthesis of 5-arylidene thiazolidinones and pyrimidinones using a novel traceless linker strategy

An efficient method for the soluble polymer-supported synthesis of 5-arylidene thiazolidinones and pyrimidinones using aniline as a traceless linker was described. Aldehyde substrates were attached to the polyethylene glycol (PEG)-bound aniline via an imine linkage, and after the subsequent PEG-promoted Suzuki coupling reaction for the diversification, Knoevenagel condensation was readily employed as the cleavage strategy.

Microwave-mediated heterocyclization to benzimidazo[2,1-b]quinazolin-12(5H)-ones

An effective route to benzimidazo[2,1-b]quinazolin-12(5H)-ones from commercially available o-aryl isothiocyanate esters and o-phenylenediamines is reported. This method accommodates a variety of substituents on either starting material and proceeds under microwave irradiation in the presence of barium hydroxide, conditions that do not hydrolyze methyl ester substituents. The pharmacologically pertinent benzimidazoquinazolinone heterocycle is delivered in excellent yield and purity via both solution- and solid-phase protocols, the latter involving traceless release from the resin.

Carbodiimide-based benzimidazole library method

Using carbodiimide reagents [1,3-diisopropylcarbodiimide or N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC)], we have developed a mild, generalized, one-pot method that delivers N-2-arylaminobenzimidazole esters from commercially available aryl isothiocyanates and o-phenylenediamines. Following saponification and acidifying, the benzimidazole acids were isolated in overall yields ranging from 75 to 88% from the starting aryl isothiocyanates. Nine benzimidazole acids were converted into a library consisting of 180 benzimidazole amides following EDC coupling with commercially available amines. The National Institute of General Medical Science will dispense these benzimidazole amides to academia groups for pilot scale biomedical studies. Using these mild conditions and environmentally safe reagents, we demonstrated that these pharmaceutically ornate heterocycles can also be constructed on solid support.

Solid-phase synthesis of the 2-aminobenzoxazole library using thioether linkage as the safety-catch linker

An efficient solid-phase methodology has been developed for the synthesis of 2-aminobenzoxazole derivatives. The key step in this procedure involves preparation of polymer-bound 2-mercaptobenzoxazole resins 3 by reaction of the Merrifield resin with 2-aminophenols and CS(2) in the presence of DIC in MeCN. Oxidation of the resulting resins followed by treatment with amines gives the desired 2-aminobenzoxazole products 5. Further diversification can be introduced to the key resin 11, derived from the nitro group containing resin 3c. This process produces the corresponding amine, which upon reaction with acid chlorides and isocyanates can be used to generate various 6-functionalized 2-aminobenzoxazole analogues 13 and 15.