A concise stereocontrolled synthesis of the racemic forms of two naturally occurring lignans, savinin (5) and gadain (6), is described. The reaction sequences used for the preparation of these lignans involve: (i) a regioselective and stereospecific Pd-mediated reaction between (3,4-methylenedioxy)phenylzinc chloride (15a) and the easily available methyl (Z)- and (E)-2,3-dibromopropenoate [(Z)- and (E)-(14)], respectively; (ii) a Pd-mediated reaction between the 3-aryl substituted 2-propenylzinc chloride (17) and the stereoisomerically pure 3-aryl-2-bromopropenoates (Z)- and (E)-16, respectively, so obtained; and (iii) treatment of the resulting dienyl esters (E)- and (Z)-18, with dicyclohexylborane followed by oxidation with 30 % H2O2 in the presence of alkali and subsequent lactonization.
A new stereocontrolled synthesis of the racemic forms of savinin and gadain
ROSSI, RENZO;BELLINA, FABIO;
1997-01-01
Abstract
A concise stereocontrolled synthesis of the racemic forms of two naturally occurring lignans, savinin (5) and gadain (6), is described. The reaction sequences used for the preparation of these lignans involve: (i) a regioselective and stereospecific Pd-mediated reaction between (3,4-methylenedioxy)phenylzinc chloride (15a) and the easily available methyl (Z)- and (E)-2,3-dibromopropenoate [(Z)- and (E)-(14)], respectively; (ii) a Pd-mediated reaction between the 3-aryl substituted 2-propenylzinc chloride (17) and the stereoisomerically pure 3-aryl-2-bromopropenoates (Z)- and (E)-16, respectively, so obtained; and (iii) treatment of the resulting dienyl esters (E)- and (Z)-18, with dicyclohexylborane followed by oxidation with 30 % H2O2 in the presence of alkali and subsequent lactonization.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
