ISSN:
0018-019X
Schlagwort(e):
Chemistry
;
Organic Chemistry
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
About the Stereospecific α-Alkylation of β-HydroxyestersIt was found, that dianions derived from β-hydroxyesters with lithium diisopropylamide (LDA) at -50 to -20° were alkylated stereospecifically (Scheme 1). The stereospecificity was 95-98%, the threo-compound (threo-2, -3 and -4) being the main product. This was proved for threo-2 and -3 by preparing the β-lactones 7 and 8, respectively, which were pyrolyzed to trans-1, 4-hexadiene (9) and trans-1-phenyl-2-butene (10), respectively (Scheme 2). Moreover, the acid threo-6 from threo-3 was converted by dimethylformamide-dimethylacetal to cis-1-phenyl-2-butene (11) (s. footnote 6).The alkylation of α-monosubstituted β-hydroxyesters also turned out to be stereospecific. Reduction of 16 and 18 with actively fermenting yeast furnished (+)-17 and (+)-2. respectively (Scheme 4), which were each mixtures of the (2R, 3S)- and the (2S, 3S)-isomers. Alkylation of (+)-17 with allyl bromide yielded after chromatography (2S, 3S)-19 and of (+)-2 with methyl iodide (2R, 3S)-19, the oxidation of which finally gave (S)-(-)-20 and (R)-(+)-20, respectively.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/hlca.19790620832
