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7749622 
Journal Article 
SYNTHETIC STUDIES ON QUASSINOIDS - TOTAL SYNTHESIS OF (-)-CHAPARRINONE, (-)-GLAUCARUBOLONE, AND (+)-GLAUCARUBINONE 
Grieco, PA; Collins, JL; Moher, ED; Fleck, TJ; Gross, RS 
1993 
Yes 
Journal of the American Chemical Society
ISSN: 0002-7863
EISSN: 1520-5126 
115 
14 
6078-6093 
English 
WOS:A1993LT17300025 
The total synthesis of (−)-chaparrinone (3), (−)-glaucarubolone (4), and (+)-glaucarubinone (5) is described. The synthesis features an intermolecular Diels-Alder reaction between dienophile 6 and (E)-4-methyl-3,5-hexadienoic acid (17) in 5.0 M lithium perchlorate-ethyl acetate. Diels-Alder adduct 16 is converted via a two-step process into tetracyclic lactone 10. Inversion of configuration at C(9) and installation of a Δ11,12 olefin in 10 provide tetracyclic lactone 19. Incorporation of the ring C functionality into 19 followed by elaboration of the ring A lβ-hydroxy-2-oxo-Δ3,4olefin unit and removal of the protecting groups on C(1) and C(12) hydroxyl groups affords pre-chaparrinone (41). Upon cleavage of the tert-butyldiphenylsilyl ether present in 41, the resultant hydroxymethyl group spontaneously closes to a C(8),C(11) bridged hemiketal giving rise to (−)-chaparrinone (3). Tetracyclic alcohol 38, an intermediate on the pathway to (−)-chaparrinone, serves as a starting point for the preparation of (−)-glaucarubolone (4). Incorporation of a C(15) hydroxyl group into 38 via tetracyclic dihydropyran 43 followed by introduction of the ring A functionality (cf. 50) and deprotection affords (−)-glaucarubolone (4). The transformation of 50 into (+)-glaucarubinone (5) features a novel reagent, (S)-(−)-5-ethyl-5-methyl-1,3-dioxolane-2,4-dione (54), for direct introduction of a C(15) α-hydroxy-α-methylbutyrate ester unit. © 1993, American Chemical Society. All rights reserved.