Synthesis of a New Pentalongin Derivative and its Saturated Analogue

The synthesis of a new derivative of pentalongin 8 and its saturated analogue 9 was ascertained. Pyridinium salt 10 was prepared by the reaction of bromoketone 11 and pyridine 12 in an excellent yield. Pyridinium ylide 10a, formed in situ, then underwent Michael addition reaction with menadione 14 to produce acylmethyl substituted naphthoquinone 15 in a high yield. The following bromination and intramolecular cyclization reaction of 15 successfully gave pentalongin derivative 8 in a good yield. The newly obtained 3,4-dehydropyranonaphthoquinone 8 was subsequently reduced to furnish the saturated analogue, pyranonaphthoquinone 9.