title: Stereoselective synthesis of 4 alpha-hydroxy-8,12-guaianolides from santonin
abstract: Hydroxyester 2, easily obtained from santonin (1), has been transformed into 10 alpha-hydroxyguai-3-en-8,12-olide 6, a good intermediate for the synthesis of natural 8,12-guaianolides. Compound 6 was obtained from 2 by photochemical rearrangement of its acetyl derivative 7, stereoselective hydrogenation on Pd/C, reduction, regioselective elimination, hydrolysis, and lactonization. The synthesis of the natural guaianolides 3-5 was carried out in two sequences in which the regioselective elimination of a hydroxyl group at C10 with triflic anhydride or SOCl2 to afford, respectively, the endo or exo double bond on C10 and the regioselective opening of the C3-C4 alpha-epoxide were the key steps.
authors.affiliation: Departamento de Quimica Organica, Facultad de Quimica, Universitat de Valencia, Spain.
authors.initials: G
authors.lastname: Blay
authors.initials: V
authors.lastname: Bargues
authors.initials: L
authors.lastname: Cardona
authors.initials: AM
authors.lastname: Collado
authors.initials: B
authors.lastname: Garcia
authors.initials: MC
authors.lastname: Munoz
authors.initials: JR
authors.lastname: Pedro