Y. El Kilany

Acyclonucleosides: Part 2. diseco-Nucleosides*

This chapter is the second of a sequence of three chapters that appears in successive volumes of this series dealing with the chemistry of acyclonucleosides. The first chapter appeared in the previous volume [97AHC391] and dealt with seco-nucleosides (one bond disconnection). This chapter deals with diseco-nucleosides (two bond disconnections). The final chapter of this series will deal with tri-, tetra-, and pentaseco-nucleosides, as well as contain an appendix of the literature that appeared after the three chapters were prepared. This chapter is the second of a sequence of three chapters that appears in successive volumes of this series dealing with the chemistry of acyclonucleosides. The first chapter appeared in the previous volume [97AHC391] and dealt with seco-nucleosides (one bond disconnection). This chapter deals with diseco-nucleosides (two bond disconnections). The final chapter of this series will deal with tri-, tetra-, and pentaseco-nucleosides, as well as contain an appendix of the literature that appeared after the three chapters were prepared.

Dimroth Rearrangement: Translocation of Heteroatoms in Heterocyclic Rings and Its Role in Ring Transformations of Heterocycles

Publisher Summary This chapter discusses the translocation of heteroatoms in heterocyclic rings and its role in ring transformation of heterocycles in dimorth rearrangement. The Dimroth rearrangement is an isomerization process whereby exoand endocyclic heteroatoms are translocated on a heterocyclic ring. It is also considered to be amidine rearrangement. This rearrangement may be classified into two main types. The translocation of heteroatoms in the first type can be between two rings of a fused system by three possible pathways: (1) an exocyclic heteroatom of a ring becomes endocyclic, (2) a heteroatom in a five-membered ring changes its location on the other ring, or (3) one of the heteroatoms of a five-membered ring becomes a substituent on the other ring and the other two heteroatoms of the same ring become a part of another five-membered ring on cyclization. The second major type involves the translocation of exo- and endocyclic heteroatoms on a single heterocyclic ring, an exoannular rearrangement, the mechanism of which has been studied since the early work on the subject. The rearrangement led to a translocation of the starred heteroatom. The Dimroth rearrangement can be catalyzed by alkali, acid, heat, or light.

Manipulation of Carbohydrate Carbon Atoms for the Synthesis of Heterocycles

This work provides an overview of the role of carbohydrates as precursors for the synthesis of heterocycles. It is limited to heterocycles where one or more of their carbon atoms are from carbohydrate reactants. A part of the sugar may remain linked to the heterocycles thus providing nucleoside analogues. The following heterocycles were included: furans, pyrrols, thiophenes, pyrazoles, imidazoles, oxazoline, dioxolanes, thiazolidines, triazoles, oxadiazoles, oxadiazolines, thiadiazoles, thiadiazolines, pyridines, pyridazines, pyrimidines, oxazines, pyrazines, quinoxalines, triazines, seven-membered rings and their fused ring systems.

Synthesis and Dimroth Rearrangement of 6-Cyano-l,2,4-triazolo- [4,3-a]pyrimidin-5- and 7-ones. A Novel Alkylation with Orthoesters and a New Participation of the Cyano Group in the Rearrangement

Abstract The cyclization products of 5-cyano-2-hydrazino-6-phenyl-3,4-dihydropyrimidin-4-one (6) with one carbon inserting agents have been confirmed to be of the 1,2,4-triazolo[4,3-a]pyrimidin- 5(8H)-ones type and not the respective 7-ones, by comparing their alkylated derivatives 10a, 11a, 27 and 28 with the product from the cyclization of the 3-methyl and 3-benzyl derivatives of 6. A novel alkylation process was found when triethyl orthoformate was used as a cyclizing agent. Dimroth rearrangement of 8, 14, 15, 24, 34 and 36 with 2% ethanolic KOH gave the respective triazolo[1,5-a]pyrimidinone 13, 18, 19, 25, 38 and 40, respectively. Using 10% ethanolic KOH led to a novel participation of the cyano group in the rearrangement whereby 8a gave 7-imino-5-phenyl-l,2,4-triazolo[1,5-a]pyrimidine 22

Synthesis of functionalised derivatives of pentaerythritol

The synthesis of functionalised derivatives of pentaerythritol has been attempted by the reaction of 1 with different aldehydes and nucleophilic reagents; the activity of various derivatives against hepatitis B virus has been studied.

Synthetic Potential Inherent in D-Isoascorbic Acid as a Precursor for Pyridazine and Furo[3,2-c]pyridazine Ring Systems with Two Asymmetric Centers

Reaction of D-erythro-2,3-hexodiulosono-1,4-lactone-2,3-bis(phenylhydrazone) (2) with an iodine, triphenylphosphine and imidazole mixture afforded the furo[3,2-c]pyridazine derivative 11. Condensation of 6-bromo-6-deoxy-D-erythro-2,3-hexodiulosono-1,4-lactone with phenylhydrazine gave the bishydrazones 6, and 8 or the furo[3,2-c]pyridazine (11) depending on the reaction conditions. The lactone ring in 11 could be opened by treatment with alkali to give the pyridazine derivative 9. Lactonization of the later with simultaneous acetylation by acetic anhydride afforded the lactone derivative 14. Alkali treatment of 6 gave the pyrazolindione derivative 13 that gave upon reation with HBr/AcO H the dibromide 15. The assigned structures were based on spectral analysis. The activity of compounds 11 and 14 against hepatitis B virus has been studied.