Synthese von verzweigten zuckern durch 1,4-addition an pyranosid-enone

Syntheses of 2,3,6-trideoxy-3-amino- and 2,3,6-trideoxy-3-nitrohexoses

“…42,43) The configuration of the C-4 hydroxyl in 46a was inverted through reaction of the mesylated 3-azido sugar 46b with sodium benzoate;44 subsequent hydrolysis produced the azido alcohol 48 with the L-lyxo configuration. Catalytic hydrogenation of 48 under acidic conditions gave the crystalline hydrochloride salt of methyl daunosaminide (49). Although no yields were reported by these authors, other investigators45,46 have used this sequence to convert the epoxide 45 to daunosamine (1) in 26% yield.…”

“…The 4,5-olefinic entity in 129 was cis hydroxylated with potassium permanganate (-40 °C, acetone; 35%), and the resultant keto alcohol 130a was reacted with hydroxylamine to produce the oxime 130b (56% yield). Catalytic hydrogenation of the oxime moiety in 130b over platinum oxide stereoselectively produced the amino glycol 131, which was hydrolyzed in acidic methanol to methyl daunosaminide hydrochloride (49).…”

“…The large number of chiral total syntheses of D-ristosamine (9) can be partially accounted for by its straightforward access from the large pool of D-hexoses. The first preparation of 9 was reported by Horton and co-workers167,168 and was derived directly from the sequence they employed for preparation of methyl daunosaminide hydrochloride (49)58 from methyl mannoside (60) (Scheme XXXIV). The amide 63 with the ribo configuration was prepared as previously discussed and shown in Scheme VI.…”

Chemische Reaktionen und Derivatisierungen ungesättigter Zucker Teil 2

“…Weitere Beispiele fur diese Reaktionen finden sich in der Literatur [195]. Fraser-Reid und Mitarbeiter untersuchten die optimalen Bedingungen fur 1,4-Additionen an Enone rnit Lithiumdialkylkupferverbindungen [196].…”

Remarkable O2-Effect in 1,4-Additions of Diethylzinc to 6-Acyloxy-2H-pyran-3(6H)-ones and 6-Alkoxy-2H-pyran-3(6H)-ones

“…Herein we wish to report the unexpected discovery of 1,4-additions of Et 2 Zn to pyranones 1 initiated by molecular oxygen, unaided by the presence of any ligand or metal catalyst. Until now, conjugate additions of carbon nucleophiles to pyranone systems have only been accomplished using Grignard reagents and organolithium-based cuprates …”