One‐pot synthesis of pyridine derivatives via diels‐alder reactions of 2,4‐dimethyl‐5‐methoxyoxazole

5‐Alkoxyoxazole – A Versatile Building Block in (Bio)organic Synthesis

“…Indeed, the presence of electron‐withdrawing groups on the olefin results in a decrease in the energy gap between the HOMO of the diene and the LUMO of the dienophile, as shown in frontier orbital energy diagram in Figure . A large variety of dienophiles have efficiently undergone the Kondrat'eva cycloaddition process, including α,β‐unsaturated enones, acrylates, fumarates, maleates, maleimides, an acrylonitrile, and an acrylic acid …”

“…A large variety of dienophiles have efficiently undergone the Kondrat'eva cycloaddition process, including α, -unsaturated enones, acrylates, fumarates, maleates, maleimides, an acrylonitrile, and an acrylic acid. [21] Figure 5. Energy of the HOMO of 5-methoxyoxazole [22] and the LUMO of unsubstituted and monosubstituted ethylene.…”

A Survey of Synthetic Routes towards the Pyranonaphthoquinone Antibiotic Pentalongin and Syntheses of the Corresponding Nitrogen Derivatives

“…In view of the physiological importance of 2-aza-anthraquinones, as outlined above, considerable efforts have been devoted to establish efficient synthetic strategies of these compounds. To date, three major synthetic pathways have been developed (Scheme 20): (i) via cycloaddition reactions of suitable dienes to isoquinoline-5,8dione or naphthoquinone derivatives 115 and 116 [81][82][83][84][85][86][87] (ii) via initial acylation of pyridines or substituted arenes followed by an intramolecular condensation/cyclization of intermediates 118 or 119 [88][89][90][91][92][93][94][95][96][97] and (iii) via construction of the heterocyclic ring starting from substituted naphthoquinones 120 or 121 [cf. the biomimetic construction of bostrycoidin starting from fusarubin ( 96)].…”

“…84 Better regioselectivities were obtained in reactions of 2-bromo-1,4-naphthoquinones with azadienes. 85 Azadiene equivalents such as thiazolidine derivatives 86 or 5-methoxyoxazoles 87 also yielded 2-aza-anthraquinones when reacted with naphthoquinone.…”

Solvent-free Photooxygenation of 5-methoxyoxazoles: Stereoselective Synthesis of α-amino-α-hydroxy Carboxylic Acid Derivatives

“…15 The key reaction is the cycloaddition of electronically excited carbonyl compounds (aldehydes and α-keto ester, respectively) to 5-methoxyoxazoles. More recently, we have developed "one-pot" synthesis of 4-substituted-3-hydroxy pyridines 16 via Diels-Alder reactions of 2,4-dimethyl-5-methoxyoxazoles with different types of dienophiles. In continuing of our work with oxazoles, we plan to explore the synthetic possibility of α-amino-α-hydroxy carboxylic acid derivatives via solvent-free photooxygenation of 5-methoxyoxazoles.…”