3-Acylindoles as versatile starting materials for pyridine ring annulation: synthesis of 1-deazapurine isosteres

One-Pot Synthesis of Novel Functionalized Fused Pyridine Derivatives via Consecutive Pyrrolidine Ring-Closure/Ring-Opening/Formal Aza-Diels-Alder Reactions

In this article, we report a highly regioselective method for the synthesis of new fused pyridine derivatives─2,3-disubstituted quinolines and 1,2-dihydro-3H-pyrazolo[3,4-b]pyridin-3-one derivatives. The method is based on the reaction of 1,1-diethoxybutane derivatives with aromatic and heterocyclic nucleophiles. The isolated compounds are similar to the products formed as a result of the Debner-Miller reaction. However, we have shown that the interaction of 1,1-diethoxybutane derivatives with (hetero)aromatic amines proceeds according to a mechanism different from that of the Doebner-Miller reaction. The proposed method is distinguished by the possibility of obtaining a wide range of substituted quinolines and 1,2-dihydro-3H-pyrazolo[3,4-b]pyridin-3-one derivatives in one step, the absence of the need to use expensive metal-containing catalysts, and a high product yield.

Synthesis of Purines and Related Molecules by Cyclization ­Reactions of Heterocyclic Enamines

A great variety of pharmacologically relevant fluorinated purine analogues are available by cyclization reactions of heterocyclic enamines with 1,3-dielectrophiles. The reactions usually proceed with excellent regioselectivities. As electrophiles, 1,3-diketones, enaminones or 3-chloro-2-en-1-ones were used. Other synthetic strategies are based on inverse-electron-demand Diels–Alder reactions of heterocyclic enamines with triazines. Purine analogues were further functionalized by transition-metal-catalyzed CH-coupling reactions or oxidative cyclizations, giving rise to more complex polycyclic products. Amidino-C-glycosides in their reactions with 1,3-dielectrophiles afforded pyrimidine-C-glycosides. Multicomponent reactions of heterocyclic enamines afforded complex products, including spirocyclic derivatives.

1 Introduction

2 1,3-Diketones

3 Enaminones

4 3-Chloro-2-en-1-ones

5 Triazines

6 Transition-Metal-Catalyzed Functionalizations

7 Pyrimidine-C-Nucleosides

8 Multicomponent Reactions

9 Conclusions