549-22-4

A general synthetic approach to rotenoids is described, featuring 1) stereospecific, group-selective 1,2-rearrangements of epoxy alcohols, and 2) S N Ar oxy-cyclizations of aryl fluorides. The common intermediate epoxyketone, en route to (-)-rotenone and (-)-deguelin, was prepared from d -araboascorbic acid in five steps. Also described is the conversion of (-)-deguelin into oxidized congeners, (-)-tephrosin and (+)-12a- epi -tephrosin.

The total syntheses of (?)-rotenone and (?)-dalpanol have been achieved by a group-selective, stereospecific 1,2-shift of an epoxy alcohol and SNAr cyclizations. Three oxacycles are constructed, thus illustrating a versatile synthetic route to various rotenoids.

Reduction of 6a,12a-didehydrorotenoids with diisobutylaluminium hydride gives clean 1,4-reduction leading to unstable trans-B/C-fusions, not previously known for enolisable rotenoids: they are epimerised to stable cis-forms under acid conditions.Applied initially to isorotenone, the method is extended to trans-B/C-deguelin, α-toxicarol, the 'core' rotenoid structure and the 6aS,12aR,5'R- and 6aR,12aS,5'R-rotenone stereoisomers. 1H and 13C NMR data are compared for the cis- and trans-forms and the geometry and conformations of the isorotenones are compared by X-ray analysis, providing insight into the reasons for the instability of the trans-forms.Reduction of the ridge-tile-like cis-isorotenone by sodium borohydride occurs from one face to give a cis-12α-hydroxy product, whilst the flatter trans-structure is attacked from both faces to give trans-12α- and 12β-hydroxy products.

Attention is drawn to a small group of diverse natural products whose biosynthesis is unusual in involving formation of O-heterocyclic rings by C-C bond formation to aromatic methoxy groups, in net oxidative and non-oxidative processes.It is shown that ar

6a,12a-Dehydrorotenoids are cleanly reduced in 1,4-fashion by DIBAL to give rotenoids having the unstable, unnatural, trans-B/C fusion, readily epimerised by acid to the cis-forms: an X-ray structure for (+/-)-trans-isorotenone confirms the nature of the ring fusion.

A reconstructive circuit for 13C- and 14C-labelling of the 7'-methylene group of (-)-rotenone is described.It involves blocking the enolisable 12a-site with a trimethylsilyloxy-group, followed by removal and reintroduction of the methylene, and elision of