Isostegane

Biomimetic oxidative coupling reactions are of interest from a mechanistic standpoint and provide particularly efficient routes to stegane and isostegane derivatives. 

Fig. 6 Synthesis of isostegane using hypervalent iodine reagent PIFA (taken from [39] by permission from Kluwer)...

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],... 

A number of biomimetic semi- or total syntheses using an oxidative coupling of a yatein or matairesinol-type intermediate to form stegane or isostegane lignans such as in Fig. (7) have been reported [35,87]. The major contributions will be reviewed in section 3.2.2. 

On the other hand, pure (-)-yatein 43, which was obtained from recrystallization of the optically enriched material furnished by path b, was sequentially converted as above to (+)-isostegane 44 and (-)-stegane 45, the latter being transformed into (-)-steganacin 2 in 61% yield by stepwise bromination, hydrolysis and acetylation [39],... 

Fig. (22). Enantioselective synthesis of (-)-isostegane by Enders [125,126] (Ar1 = piperonyl, Ar2 = 3,4,5-trimethoxyphenyl)...

Arctigenin (472), prepared from 3,4-dimethoxybenzaldehyde, was submitted to PhI(OCOCF3)2-promoted oxidation in trifluoroethanol (TFE) (room temp., 24 h) to afford spirodienone 473 and a mixture of two cyclooctadienes (474 and 475) in 13 and 14% yields, respectively. When the reaction was repeated in hexafluoroisopropanol for 3.5 h, a 1 1 mixture of stegaue 474 and isostegane 475 was obtained in 26% yield (Scheme 93). Acid-catalyzed rearrangement of 473 with HCIO4 in CHCI3 provided a quantitative... 

Fig. (7). Biomimetic synthesis of racemic isostegane [84] (TFA = trifluoroacetic acid)...

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