Alkenes lignans synthesis

An interesting application of the asymmetric alkoxyselenenylation of alkenes to natural product synthesis was reported recently by Wirth, who described a short procedure to obtain some furofuran lignans 147]. The total synthesis of (+)-Samin 53 [47 a] is shown in Scheme 7. The protected allylic alcohol 50 was treated with the selenyl triflate derived from diselenide 29 in the presence of 2,3-butadien-l-ol, and afforded the addition product 51 in 55% yield and with a diastereomeric ratio of 15 1. The favored 5-exo-trig radical cyclization of the major isomer afforded the tetrahydrofuran derivative 52 from which the final product was obtained through few classical steps. 

Molander s research group employed an 8-endo-trig car-bonyl-alkene cyclization for the final step of their total synthesis of isoschizandrin, a dibenzocyclooctadiene lignan isolated from the fruit of Schizandra chinesis, a creeping vine native to northern China. The final intermediate, optically active biaryl compound 129 was treated with Sml2 in the presence of rBuOH and HMPA to provide isoschizandrin (130) in 85% yield as a >18 1 mixture of diastereo-mers (Scheme 25.62). 

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