Pyridinium‐Ionen in Nachbarschaft zu Oxiranringen: nützliche Zwischenstufen zur stereospezifischen Synthese von β‐Hydroxyketonen

Abstract

α,β‐Epoxytriflate wie das Epoxytriflatpyranosid 1 lassen sich in einer Eintopfreaktion nach Umsetzung mil Pyridin unter Öffnung des Epoxyrings zu N‐Vinylpyridiniumderivaten (z.B. 2) umlagern, welche nach Reduktion mit NaBH4 und saurer Hydrolyse β‐Hydroxyketone liefern. Mit dem allgemein anwendbaren Verfahren lassen sich z.B. leicht zugängliche Epoxypyranosen in hoher Ausbeute in Desoxyketozucker wie 3 überführen.

On the Michael Addition of Water to α,β‐Unsaturated Ketones Using Amino Acids

“…Another route involves the hydrogenolysis of β‐epoxy ketones using, for example, Bu 3 SnH/Bu 3 SnI/phosphine oxide18 or [Cp 2 TiCl] 19. Also, the pyridinium‐assisted ring‐opening of epoxide rings followed by NaBH 4 reduction has been described 20. Although intramolecular aldolization of keto aldehydes is rarely employed, good results have been obtained by using triazabicyclo[4.4.0]dec‐5‐ene (TBD) as base 21.…”

Towards Highly Activating Leaving Groups: Studies on the Preparation of Some Halogenated Alkyl Sulfonates

“…During the esterification of sterically congested alcohols with triflic anhydride, the formation of sulfur(IV) esters (sulfinates) has been detected, depending on the base and conditions applied [ 14 ]. If pyridine is used as a (standard) base and solvent, pyridinium salts may be formed due to the high reactivity of triflates [ 15 ].…”