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Paper | Special issue | Vol 99, No. 2, 2019, pp.1073-1085
Published online, 12th December, 2018
DOI: 10.3987/COM-18-S(F)73
Asymmetric Synthesis of 2,3-Dimethoxy-8-oxoberbine, Precursor of O-Methylbharatamine

Maria Chrzanowska,* Agnieszka Dreas, and Zofia Meissner

*Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b, 61-614 Poznań, Poland

Abstract

The enantiospecific and enantioselective syntheses of 2,3-dimethoxy-8-oxoberbine were performed using the lateral metallation methodology. In the enantiospecific synthesis (4S)-2,2,4-trimethyl-3-(o-toluoyl)oxazolidine incorporating (S)-alaninol as the chiral auxiliary was applied. The addition reaction of benzylic anion generated in situ from chiral oxazolidine into 6,7-dimethoxy-3,4-dihydroisoquinoline led to the protoberberine with high enantiomeric excess. Enantioselective synthesis of 2,3-dimethoxy-8-oxoberbine was performed with achiral 2,2-dimethyl-3-(o-toluoyl)oxazolidine in the presence of chiral ligands. Among them (–)-sparteine and (+)-sparteine surrogate turned out to be the most efficient ones.