Of -stegane

Another clue for the biogenesis of steganes was given by the early work of Schlessinger and co-workers, who reported the biomimetic total synthesis of ( )-isostegane, Fig. (7) [84],... 

Phenolic or non-phenolic oxidative coupling methods have been extensively used since the 1970 s to synthesize polyoxygenated bridged biaryl compounds, as will be illustrated later in the case of steganes. Remarkably enough, the use of transition metal oxidants is particularly suited to perform intramolecular biaryl coupling whereas most other methods are better suited to intermodular coupling. 

Further studies described the interconversion of stegane diastereoisomers via thermal (for the biaryl axis) or acid/base-induced (for the a-lactone position) processes, Fig. (18) [110,111,112], These isomerization possibilities were largely exploited in the different total syntheses discussed in the following pages. 

Tab. 28. Survey of oxidants for the intramolecular cyclization of stegane precursors.

Ward, Pelter, and co-workers have documented the efficacy of in situ generated ruthenium tetrakis(trifluoroacetate) (following the work of Robin and Landais) [126, 127] as a useful reagent for the synthesis of a large number of stegane-like molecules [123]. In the transfused butyrolactone series 180, single diastereomers 181 are usually obtained (Scheme 43a). If cis-fused butyrolactones 182 are used as precursors, the biaryl products are formed as a mixture of atropisomers 183 and 184 (Scheme 43b). 

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