Synthesis of Shikonin and Alkannin

✍ Scribed by Braun, Manfred ;Bauer, Claus

• Publisher: John Wiley and Sons
• Year: 1991
• Tongue: English
• Weight: 867 KB
• Volume: 1991
• Category: Article
• ISSN: 0947-3440
• DOI: 10.1002/jlac.1991199101199

✦ Synopsis

Abstract

The enantiomeric naturally occurring naphthoquinones shikonin [(R)‐1] and alkannin [(S)‐1] have been synthesized in a thirteen‐step procedure in 44 to 65% e.e. The stereogenic centers of (R)‐1 and (S) are created by the reaction of naphthaldehyde 3 with (R)‐ and (S)‐2‐hydroxy‐1,2,2‐triphenylethyl acetate (2), respectively. In order to find out a rationalization for the unexpectedly low diastereoselectivity in this aldol addition, a series of substituted aromatic aldehydes 12a–h has been treated with (R)‐2.