Titanocene(III) chloride mediated radical induced addition-elimination route to the synthesis of racemic and optically active trisubstituted tetrahydrofurans: Formal synthesis of magnofargesin and 7′-epimagnofargesin

Abstract

Titanocene(III) Chloride mediated radical induced synthesis of 4-benzylidene substituted tetrahydrofuran, a typical lignan skeleton, has been accomplished in good yield through addition-elimination route in racemic as well as in optically active forms. The method has been applied to the synthesis of furano lignans, magnofargesin (1) and 7-epimagnofargesin (2) in optically active forms.

Cobalt-Catalyzed Asymmetric Hydroboration/Cyclization of 1,6-Enynes with Pinacolborane

“…Furthermore, we showed that an enantiomerically pure 1,6-enyne 7 underwent a diastereo­selective hydroboration/cyclization, yielding an alkyl boronate ester 8 , isolated as a single diastereomer in 76% yield (Scheme B). Finally, the synthesis of (−)-magno­fargesin ( 10 ) (Scheme C) was achieved in 33% yield with 94% ee via the reaction sequence of the diastereo-divergent hydroboration/cyclization of enyne rac - 9 and oxidation of the resulting alkyl boronate ester with H 2 O 2 in the presence of aqueous NaOH solution …”

Total Synthesis of Leoligin from Edelweiss Roots

“…21 Chakraborty and co-workers used a titanocene (III) chloride-mediated radical-induced additionelimination route for the synthesis of racemic and optically active trisubstituted tetrahydrofuran lignans. 22 Yamauchi et al synthesised (+)-dihydrosesamin, a trisubstituted tetrahydrofuran-type lignan by using a highly erythro-selective aldol condensation. 23 Here we describe a seven-step synthesis of the tetrahydrofuran lignan, leoligin (Fig.…”