Enantioselective Synthesis of a Polyfunctionalized Tetracycle Related to Pentacyclic Triterpenes by Using an Anionic Cycloaddition Reaction

✍ Scribed by Alain Rouillard; Marc-André Bonin; Pierre Deslongchamps

• Book ID: 102256212
• Publisher: John Wiley and Sons
• Year: 2003
• Tongue: German
• Weight: 172 KB
• Volume: 86
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.200390315

✦ Synopsis

Abstract

Herein we report a convergent enantioselective synthesis of a polyfunctionalized ABCD tetracycle by using an anionic cycloaddition reaction between a chiral bicyclic CD Nazarov intermediate (see 6), derived from the (−)‐Weiland–Mischer ketone, and an achiral cyclohexenone (see 5) adequately functionalized to furnish the ring A of pentacyclic triterpenes (Scheme 5). The chiral bicyclic CD Nazarov intermediate forms ring B upon cycloaddition with the achiral cyclohexenone to yield an ABCD tetracycle with a cis‐anti‐trans‐anti‐trans configuration (see 4). Further transformations on this adduct allowed reduction of the angular aldehyde function at C(10) to a Me group (→17) and introduction of an unsaturation at C(5)C(6) by using the ketone function at C(7) (→ 3; Scheme 6).