Chiral synthesis and stomatal closure activities of γ-pseudo- and dihydro-abscisic acids
摘要:
Analogues of abscisic acid (ABA) were prepared from chiral cyclohexanone building blocks. Synthetic (1'R, 3'S)-1',3'-gamma-dihydroxy-gamma-ionylideneacetic acid and (R)-1'-hydroxy-3'-oxo-gamma-ionylideneacetic acid (tentatively named gamma-pseudo-ABA) provided authentic data for new metabolities isolated from Cercospora cruenta. Both enantiomers of 2', 3'-dihydroABA were also prepared. Only the (1'S, 2'S)-isomer of 2', 3'-dihydroABA induced substantial closure of stomata on the epidermal strips of Commelina communis.
Enantioselective Synthesis of Chromans for the Preparation of Enantiopure Vitamin E and Analogues
作者:Lutz F. Tietze、Jochen Görlitzer
DOI:10.1055/s-1997-1278
日期:1997.8
Coupling of the different protected (hydroxymethyl)enynes 11a-e and 12a-c with the iodoarene 7 in the presence of catalytic amounts of Pd(PPh3)4 afforded the arylenynes 5a-e and 6a-c which were transformed into the monoprotected chiral trihydroxy compounds 13a-d and 14a,b by Sharpless bishydroxylation with >95% ee for 13a-d, 91% ee for 14b and 64% ee for 14a. A 5-step transformation of 13a led to the desired chroman derivative 3a which was cleaved to give the aldehyde 2 a known precursor for the enantioselective synthesis of vitamin E.
6-Endo- and 5-exo-digonal cyclizations of o-hydroxyphenyl ethynyl ketones: A key step for highly selective benzopyranone formation
作者:Kazuhiko Nakatani、Akimitsu Okamoto、Isao Saito
DOI:10.1016/0040-4020(96)00480-2
日期:1996.7
critical for the products formation. We generated phenoxide ion under aprotic conditions in situ by desilylation of o-silyloxyphenyl ethynyl ketones with spray dried potassium fluoride and 18-crown-6 in anhydrous DMF. Under these conditions the cyclization of variety o-hydroxyphenyl ethynyl ketones proceeded smoothly to produce benzopyranone derivatives with exceedingly high selectivity. Theoretical and experimental
Pd(0)-catalyzed carbonylation of (Z)-2-en-4-yn carbonates in the presence of a balloon pressure of CO in an alcohol donates vinylallenyl esters with an exclusively E-configuration and in high yields. The fact that no such reactivity could be observed with E-configured enyne carbonates may indicate that the reaction is promoted via the cooperative coordination of palladium with both alkynyl and carbonate moieties.