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Enantioselective Synthesis of a Polyfunctionalized Tetracycle Related to Pentacyclic Triterpenes by Using an Anionic Cycloaddition Reaction
Author(s) -
Rouillard Alain,
Bonin MarcAndré,
Deslongchamps Pierre
Publication year - 2003
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.200390315
Subject(s) - chemistry , cycloaddition , enantioselective synthesis , ketone , bicyclic molecule , cyclohexenone , stereochemistry , aldehyde , ring (chemistry) , organic chemistry , catalysis
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 ).