Abstract
The present article provides an overview of our work related to cyclization reactions of nitro-substituted electrophilic building blocks with various nucleophiles. As electrophiles, we used nitro-substituted benzoylacetones, 3-ethoxy-2-nitro-2-en-1-ones, 2-nitrobenzoyl chlorides, 4-chloro-3-nitrocoumarin, 2-nitromalonic aldehyde, 3-nitrochromone and 1-(2-chloro-5-nitrophenyl)prop-2-yn-1-ones. As nucleophiles, 1,3-dicarbonyl compounds, 1,3-bis(silyloxy)-1,3-butadienes, (heterocyclic) enamines, hydroxylamine, hydrazines, amines and amino esters were employed. The products include a variety of nitro-substituted carbo- and heterocycles that are not readily available by other methods. The electron-withdrawing nitro group can be easily transformed into an electron-donating amino group which is not only pharmacologically relevant, but can also act as a nucleophile in inter- and intramolecular reactions with electrophiles, such as aldehydes, and can be converted into other functional groups. The nitro group has the capacity to activate compounds for regioselective palladium-catalyzed CH-arylation reactions. Inter- and intramolecular CH arylations of nitro-substituted heterocyclic building blocks, such as 4-nitropyrazoles, 4-nitroimidazoles, 2-nitroindole and nitro-substituted purine analogues, allow for a convenient diversity-oriented approach to the corresponding arylated products. In addition, the nitro group can act as a leaving group in SNAr reactions. Various fused benzofuro[3,2-b]pyridines were prepared by intramolecular SNAr reactions of 2-(hydroxyphenyl)-3-nitropyridines.
1 Introduction
2 Cyclizations of 1,3-Bis(silyloxy)-1,3-butadienes
3 Cyclizations of Heterocyclic Enamines
4 Reactions of Simple Nitro-Substituted Heterocycles
5 Hydroamination Reactions of Alkynes
6 Miscellaneous
7 Conclusions
Key words
amines - cyclization - enamines - heterocycles - nitro compounds - regioselectivty
