Functionally substituted vinyl carbanions, 43. Convenient transformation of hexopyranosides into α‐methylene δ‐lactone derivatives

Abstract

Treatment of glycopyranosyl phenyl sulfoxides 2ah, 1, 2bh, 1 with two equivalents of lithium diisopropylamide provides directly the C‐2‐lithiated glycal intermediates 3aAh, 1, 3bAh, 1 which, on reaction with formaldehyde as electrophile, furnish the 2‐hydroxymethyl derivatives 4ah, 1 and 4bh, 1, respectively. These compounds are transformed at elevated temperature and by acid catalysis directly into the α‐methylene‐δ‐lactones 5a, b. Correspondingly, from 2ah, 1 and methyl chloroformate as electrophile the 2‐methoxycarbonyl derivatives 6h and 61, respectively, are obtained. Treatment of 6h, 1 with Raney nickel leads to 2‐methoxycarbonyl‐substituted glycal 7 containing a β‐alkoxyacrylate moiety which again can be directly β‐C‐lithiated as demonstrated by the introduction of deuterium at C‐1.

Diversity‐Oriented Synthetic Endeavors of Newly Designed Ferrier and Ferrier‐Nicholas Systems Derived from 1‐C‐Alkynyl‐2‐deoxy‐2‐C‐Methylene Pyranosides

“…Silica gel chromatography (hexane/ethyl acetate, 65:35) provided pure 20a (267 mg, 98 %) as a colorless oil. This material gave satisfactory spectral and analytical data, comparable with the literature values …”

Gold Catalysis for Heterocyclic Chemistry: A Representative Case Study on Pyrone Natural Products

“…Tr eatment with excess LDAr esulted in lithiation of the glycal first formed;t he regioselectivity is determined by the directing effect of the sulfoxide. [74] Intermediate 67 was quenched with trimethylsilylethyl chloroformate to give ester 68.AMichael/retro-Michael addition reaction then furnished the required acetylene derivative 70,w hich underwent the envisaged gold-…”

“…Standard protecting‐group and oxidation‐state management allowed 65 to be converted into the sulfoxide derivative 66 (Scheme ). Treatment with excess LDA resulted in lithiation of the glycal first formed; the regioselectivity is determined by the directing effect of the sulfoxide . Intermediate 67 was quenched with trimethylsilylethyl chloroformate to give ester 68 .…”

Gold‐Katalyse für die Heterocyclenchemie: eine repräsentative Fallstudie zu Naturstoffen der Pyron‐Reihe

“…Verbindung 65 wurde auf bekanntem Weg in das Sulfoxid 66 überführt (Schema ). Bei Umsetzung mit LDA bildet sich daraus zunächst ein Glycal, das durch den eingesetzten Reagenzüberschuss sofort lithiiert wird, wobei sich die Regiochemie aus dem dirigierenden Einfluss der Sulfoxid‐Einheit ergibt . Abfangen von 67 mit Chlorameisensäure(trimethylsilylethyl)ester lieferte Verbindung 68 , die durch Michael/Retro‐Michael‐Reaktion zum Alkin 70 umgesetzt wurde.…”