Conversion of a Benzofuran Ester to an Amide through an Enamine Lactone Pathway: Synthesis of HCV Polymerase Inhibitor GSK852A.

HCV NS5B polymerase inhibitor GSK852A (1) was synthesized in only five steps from ethyl 4-fluorobenzoylacetate (3) in 46% overall yield. Key to the efficient route was the synthesis of the highly functionalized benzofuran core 15 from the ß-keto ester in one pot and the efficient conversion of ester 6 to amide 19 via enamine lactone 22. Serendipitous events led to identification of the isolable enamine lactone intermediate 22. Single crystal X-ray diffraction and NMR studies supported the intramolecular hydrogen bond shown in enamine lactone 22. The hydrogen bond was considered an enabler in the proposed pathway from ester 6 to enamine lactone 22 and its rearrangement to amide 19. GSK852A (1) was obtained after reductive amination and mesylation with conditions amenable to the presence of the boronic acid moiety which was considered important for the desirable pharmacokinetics of 1. The overall yield of 46% in five steps was a significant improvement to the previous synthesis from the same ß-keto ester in 5% yield over 13 steps.

An enyne cycloisomerization approach to the triple reuptake inhibitor GSK1360707F.

The triple reuptake inhibitor GSK1360707F was synthesized via an efficient and scalable route that features an enyne cycloisomerization reaction catalyzed by either Pt(II) or Au(I). Key aspects of this work such as the choice of the nitrogen protecting group and initial enantioselectivity studies are discussed.

Rhodium(I)-catalyzed [2+2+1] cycloadditions of 1,3-dienes, alkenes, and CO.

Initial examples of a Rh(I)-catalyzed [2+2+1] reaction of diene-enes and CO are described. This method allows for the facile, efficient, and diastereoselective construction of a variety of alkenyl cyclopentanones in good to excellent yields. Control studies show that the diene moiety is required for this process as bis-enes do not give the [2+2+1] products under the same conditions.