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1 Introduction [2+2] Cycloadditions of electron-poor acetylenes to push–pull systems, such as 3-(dimethylamino)propenoates, acyclic and cyclic enamines, and some heterocyclic enaminones, have been described recently [ 1 ]. Polysubstituted butadienes have been prepared by microwave-assisted [2+2] cycloadditions of enaminones to electron-poor acetylenes [ 2 ], [ 3 ]. Polysubstituted aminobutadienes prepared by this procedure are suitable for the preparation of polysubstituted pyridine derivatives. They also represent a group of isomeric intermediates in regard to

1 Introduction 3-Dimethylaminopropenoates and related enaminones have been demonstrated to exhibit a broad applicability in heterocyclic synthesis [ 1 – 5 ], including the preparation of natural products and their analogues, such as aplysinopsins [ 6 , 7 ], meridianines [ 8 , 9 ], and dipodazines [ 10 – 12 ]. Recently, polysubstituted butadienes have been prepared by microwave-assisted [2+2] cycloadditions of enaminones to electron-poor acetylenes [ 13 , 14 ]. Polysubstituted aminobutadienes prepared by this procedure are suitable for the preparation of

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, Jan C. Namyslo and Andreas Schmidt Chemistry and spectroscopy of cross-conjugated and pseudo-cross-conjugated quinolinium-ethynyl-benzoate mesomeric betaines 481 Dörthe Jakobi, André Schumann and Rainer Beckert Integrating the fluorene substructure into azaacenes: syntheses of novel fluorophores 493 Benjamin Prek, Marta Počkaj, Willi Kantlehner and Branko Stanovnik Thermal metal-free [2+2] cycloaddition of acetylenedicarboxylates to polysubstituted butadienes 501 Maren Muntzeck and René Wilhelm Protic ionic liquids as catalysts for a three

[43 – 45]. Recently, polysubstituted butadienes have been prepared by microwave-assisted [2+2] cycloadditions of enam- inones to electron-poor acetylenes [46, 47]. Polysubstituted aminobutadienes prepared by this procedure are suitable for the preparation of poly- substituted pyridine derivatives. They also represent a group of isomeric intermediates in regard to the aminobutadienes prepared via the Michael addition in Bohlmann-Rahtz syntheses of pyridine deriva- tives [48, 49]. On this basis, a simple metal-free synthesis of 2-alkyl-, 2-cycloalkyl-, 2-aryl-, and 2