Synthesis of 2′,3′-dideoxy-6′-fluorocarbocyclic nucleosides via Reformatskii–Claisen rearrangement

Recent progress for the synthesis of selected carbocyclic nucleosides

Nucleoside analogs are extremely useful for the development of therapeutic agents to control viral diseases and cancer. Among the numerous modifications on the nucleoside skeleton, replacement of the oxygen of the furanose ring by a CH2 group resulted in increased flexibility and higher resistance to phosphorylases and led to carbocyclic nucleoside analogs (or carbanucleosides). The broad spectrum of biological activities of carbocyclic nucleosides led to tremendous research interest in their syntheses. The article documents recent strategies for the synthesis of active carbocyclic nucleosides by presenting individual case studies, such as the neplanocins, entecavir and selected fluorinated carbocyclic nucleosides. Furthermore, it provides new insights into new directions for more potent and active carbocyclic nucleoside analogs.

Reversal of facial selectivity in a thia-Claisen rearrangement by incorporation of a vinylic bromine substituent

Thia-Claisen rearrangements have been carried out using N-benzylpyrrolidine-2-thione and chiral allylic bromides derived from D-mannitol. Introduction of a bromine atom onto the double bond of the allylic bromide reverses the sense of diastereoselectivity in the [3,3]-sigmatropic rearrangement. Density functional theory calculations lead us to rationalise the observed selectivity in terms of a Cíeplak effect.

Recent developments in the Reformatsky-Claisen rearrangement

The rearrangement of allyl α-bromoacetates with Zn dust is known as the Reformatsky-Claisen rearrangement. Whereas the Ireland-Claisen rearrangement has been widely used in the synthesis of a diverse range of natural products, the Zn-mediated Reformatsky-Claisen rearrangement has not been utilized so often. In this article, we will provide an overview of recent advances in the Reformatsky-Claisen rearrangement field, including the In-mediated Reformatsky-Claisen rearrangement we have recently developed.