Arylnaphthalene lignans

Domino processes involving Homer-Wadsworth-Emmons (HWE) reactions constitute another important approach. Among others, HWE/Michael sequences have been employed by the group of Rapoport for the synthesis of all-cis-substituted pyrrolidines [143], and by Davis and coworkers to access new specific gly-coamidase inhibitors [144]. Likewise, arylnaphthalene lignans, namely justicidin B (2-281) and retrojusticidin B (2-282) [145], have been synthesized utilizing a domino HWE/aldol condensation protocol developed by Harrowven s group (Scheme 2.65) [146]. 

Regioselective hydrogenation of anhydrides to lactones. The last step in the synthesis of arylnaphthalene lignans is usually selective hydrogenation of an an-... 

Sarkar and coworkers reported a route from which heterocyclic analogs of 1-arylnaphthalene lignans were synthesized via a sequential Pummerer-Diels-Alder pathway, featuring furo[3,4-c]pyridines as intermediates. An example is depicted below <03JOC6919>. 

T Kuroda, K Kondo, T Iwasaki, A Ohtani, K Takashima. Synthesis and hypolipidemic activity of diesters of arylnaphthalene lignan and their heteroaromatic analogs. Chem Pharm BulU5 67S-6M, 1997. 

A protocol for constructing biaryls by the palladium(O)-catalyzed [2+2+2] cocy-cUzation of arynes with diynes has been developed by Sato and coworkers (Scheme 12.63). Total syntheses of the arylnaphthalene lignans taiwanin C, taiwanin E and dehydrodesoxypodophyUotoxin have been achieved by employing a [2-I-2-I-2] cocy-cHzahon as a key step [121]. 

The Pummerer rearrangement can also be carried in tandem with a Diels-Alder reaction. This sequence has been utilized in the syntheses of the arylnaphthalene lignan natural products. Sulphoxide 64 in acetic anhydride was slowly added to a solution of dimethyl maleate in acetic anhydride under reflux, resulting in cycloadduct 65 in 85% yield. 

Annapoorani K S, Damodaran C, Sekharan P C 1984 Solid-state fluorodensitometric quantitation of arylnaphthalene lignan lactones of Cleistanthus collinus. J Chromatogr 303 296-305... 

Another interesting example of phenylpropanoid coupling was reported from Bupleurum salicifolium (44). In this regard, an H2O2-dependent peroxidase was isolated, which converts either caffeic 8 or ferulic 9 acids, into 8.8 -bis (caffeic acid) and 8.8 -bis (ferulic acid), respectively. Although a role was proposed for these compounds in the synthesis of more elaborate arylnaphthalene lignan skeleta, this has not been established. 

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