Jl. Charlton et Gl. Chee, ASYMMETRIC-SYNTHESIS OF LIGNANS USING OXAZOLIDINONES AS CHIRAL AUXILIARIES, Canadian journal of chemistry, 75(8), 1997, pp. 1076-1083
A simple procedure for the asymmetric synthesis of lignans via chiral
beta-benzyl-gamma-butyrolactones has been developed. The key benzylbut
yrolactone intermediates were efficiently synthesized using a six-step
procedure, starting from 3,4-(methylenedioxy)cinnamic acid. The key s
tep in this sequence was a highly diastereoselective alkylation of an
N-acyloxazolidinone enolate. The resulting beta-benzyl-gamma-butyrolac
tones were subsequently transformed into the benzylidene lignans gossy
pifan and savinin (hibalactone) via aldol condensation-dehydration rea
ctions, and into the dibenzylbutyrolactone lignan 4'-demethylyatein, t
hrough alkylation. Oxidation of 4'-demethylyatein with 2,3-dichloro-5,
6-dicyano-1,4-benzoquinone (DDQ) afforded cis-and trans-benzylideneben
zylbutyrolactones, whereas oxidation with DDQ/TFA gave 4'-demethyldeox
yisopodophyllotoxin.