Tetrahydrofuran lignans

This is the smallest group of lignan tetrahydrofurans with fewer than ten members. All of reasonably well defined constitution are 3,4-trarw-disubstituted. Of these, most attention has been directed towards burseran, a constituent of Bursera microphylla with tumour-inhibiting properties (82). Optically pure (-)-/ra/w-burseran (82) and (-f-)-cw-burseran (83) were stereoselectively synthesized from chiral butyrolactones and gas chromatographic comparison indicated that the natural... 

Lopes NP, Yoshida M, Kato MJ (2004) Biosynthesis of tetrahydrofuran lignans in Virvla surinamensis. Brazil J Pharm Sci 40 53-57... 

Two different classes of optically active a-hydroxylated lignans have been prepared from sugars by Yamauchi and co-workers lactone lignans [47, 48] and tetrahydrofuran lignans [49, 50]. In both cases, only model compounds were synthesized, such as lactone lignan 55 (Scheme 13), as a result of the synthetic strategy. The key intermediate for the synthesis of lactone lignan... 

The bis(silyloxy)furans also react with substituted benzaldehydes in the presence of titanium tetrachloride to give diaryldioxabicyclo[3.3.0]octane-4,8-diones (39 equation 1) (80TL3427). Bis-lactones of this structure type have been isolated from the cultured mushroom Inonotus sp. K-1410. The bis(silyloxy)furans also hold promise for the construction of natural lignans that exhibit a skeleton made up of two fused tetrahydrofuran ring systems. 

Finally, two tetrahydrofurofuran lignans (the stereoisomers asarinin and sesamin, Scheme 12) have been subjected to MTO-catalyzed oxidation. In both cases, the major product originates from oxidative cleavage of one of the phenyl-tetrahydrofuran bonds yielding a lactone. In a CH2Cl2/MeCN mixture using UHP as the oxidant, 65% conversion and 87% selectivity for the lactone is obtained. With immobilized MTO/PVP-2% as catalyst in CH2Cl2/EtOH, similar results are obtained [95]. 

Indolines and indoles were prepared by a direct electrochemical reduction of arenediazonium salts. As a result, radical intermediates were generated from which 3,4-disubstituted tetrahydrofuran skeleta were constructed <02OL2735>. A short and stereoselective total synthesis of furano lignans was realized by radical cyclization of epoxides using a transition-metal radical source <02JOC3242>. Other preparations of tetrahydrofurans using radical cyclization include the synthesis of novel amino acids L-bis-... 

An application of this methodology to the synthesis of several tetrahydrofuran lignan derivatives having trypanocidal activity was further reported by Kato and co-workers [62]. This sequential palladium-mediated Michael... 

In the total syntheses of 2,5-diaryl-3,4-dimethyltetrahydrofuran lignans (-f )-fragrasin (-f)-galbelgin, (-f)-talau-midin, (—)-saucernetin, and (—)-verrucosin, a novel ring closure to tetrasubstituted tetrahydrofurans by intramolecular attack on a quinoid intermediate has been described <2007SL475>. 

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. 

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