A new efficient route for multigram asymmetric synthesis of alkannin and shikonin.
A short and convergent approach for the synthesis of alkannin, shikonin and shikalkin is presented. A Hauser-type annulation of cyanophthalide 26 with enone 7 affords the complete aromatic system in just one step with concomitant attachment of the entire side chain. Subsequent Corey's oxazaborolidine mediated asymmetric reduction of the above advanced intermediate, leads to the required isomer in high enantiomeric excess. Finally, a selective and high yielding deprotection protocol furnishes the title compounds as pure crystalline precipitates. Thus, a multigram synthesis of shikonin, alkannin and shikalkin is achieved in high yield and enantioselectivity.
Couladouros
Elias A
EA
Chemistry Laboratories, Agricultural University of Athens, Iera Odos 75, Athens 118.55, Greece. ecoula@mail.demokritos.gr
Strongilos
Alexandros T
AT
Papageorgiou
Vassilios P
VP
Plyta
Zoi F
ZF
D001372:Aza Compounds / Q000737:chemistry*; D002712:Chlorides / Q000737:chemistry; D003035:Cobalt / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004583:Electrons; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000032:analysis / Q000737:chemistry*
D001372:Aza Compounds; D002712:Chlorides; D009942:Organometallic Compounds; D003035:Cobalt