Dibenzylbutyrolactone-type lignan

Another Cyclization Reaction of 2,3-Dibenzylbutyrolactone Type Lignan to... 

Fig. 6.13 Furofuran and dibenzylbutyrolactone type lignans isolated from convolvulaceous species (glu = P-D-glucose api = P-D-apiose xyl = P-D-xylose). The arrows in the structure of pinoresinol indicate that this bond is not existing in the structure of lariciresinol, i.e., there is a free hydroxyl group which is glycosylated in case of its 9-glucoside (a constituent of Solarium tuberosum, Solanaceae)...

The lignans are a large group of plant phenolics, biosynthesized from the union of two phenylpropane molecules e.g., both matairesinol (Centaurea species, family Asteraceae) and podophyllotoxin Podophyllum peltatum, family Berberidaceae) are formed from the phenylpropane coniferyl alcohol. Lignans are essentially cinnamoyl alcohol dimers, though further cyclization and other structural modifications result in various structural types, e.g. dibenzylbutyrolactone and epoxy lignan. 

Another simple synthesis of lignans of the lariciresinol type (11) involves a straightforward reduction of a functionalised dibenzylbutyrolactone such as (75) or (76) followed by acid-catalysed cyclisation (scheme 24) [77,78]. Cyclisation of the doubly functionalised precursor (77) affords access to the furofuran skeleton (78) (scheme 25). A second synthesis which has also been extended to the furofuran series involves a radical cyclisation step, which proceeds with high stereoselectivity (scheme 26) [79]. This route has been used to synthesise (79) which is a precursor for the synthesis of sesamin and eudesmin [80]. 

As already demonstrated tra 5-dibenzylbutyrolactones are valuable as precursors for the synthesis of a wide range of lignans. For example, the keto-lactones (90) and (91), which have both been prepared by tandem conjugate addition reactions, provide key intermediates for the synthesis and asymmetric synthesis respectively of lignans of the furofuran type (scheme 30) [85,86]. 

Dibenzylbutane derivatives and dibenzylbutyrolactones undergo a wide range of interesting reactions, frequently leading to other lignan types. For... 

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