Methoden und Möglichkeiten der nucleophilen Acylierung

Abstract

ist der Stickstoff mit groDer Wahrscheinlichkeit ,,endon'' gebunden. Fur ,,edge-on" gebundene N2-Molekule fehlt aber ein so einfaches Nachweisverfahren wie die IR-Bande bei ca. 2100 cm-1 fur ,,end-on". Die Reaktionsweise des Wassers wird dabei, wenn man nur Ausgangs-und Endprodukt betrachtet, umgekehrt. Man kann dies auch eine ,,Symmetrisierung" [31 der Reaktivitat nennen (Schema 1).

d5‐Reactions of Doubly Deprotonated γ,δ‐Unsaturated Carbonyl Derivatives with Electrophiles. A Novel Approach to the Synthesis of Tetrahydrofuran and Tetrahydropyran Derivatives

“…Acylation of 1 does not appear to be a favorable process: methyl isobutyrate converts l b to the 1,6-diketone12) 5 in 23% yield only; besides 2% of the diadduct, a 6-hydroxy-l,ll-diketone, the product of a kinetic protonation') of lb, the p, y-unsaturated ketone'), is isolated. Attempts to acylate 1 with the non-enolisable methyl benzoate were also unsatisfactory.…”

“…65, Fasc. 2 (1982) In view of the great tendency of sulfur-containing allylic and pentadienylic anion derivatives [5] to steer reactivity to the C-atom a to sulfurL3) [7], it is not surprising that the reagents l e and If (X = S), are not as ambido~electivel~) as their analogues la-d (where X = 0): besides the d5-products 6f, the d3-products of type 8 are formed in 2-10% yield (see Table I). They are easily separated during chromatographic isolation of 6f; only the adduct 8 to cyclopentanone was obtained in a pure state and was fully characterized.…”

“…The alkoxide-thioenolates primarily formed from benzaldehyde and benzophenone and If can not only be quenched with acid (+ 6fd and 6fh, respectively) but also with methyl iodide which leads to the unsaturated conjugated keten thioacetal derivatives 9 after aqueous workup' j). This represents a novel synthetic approach to this versatile class of compounds [5] [7]. We have deprotonated 9b with excess lithium diisopropylamide (LDA), and quenched the resulting alkoxide-pentadienyl-anion derivative with acid (-+ lOa), methyl iodide (+ lob) and ethyl iodide (+ 1Oc).…”

Aldehyde N,N‐Dialkylhydrazones as Neutral Acyl Anion Equivalents: Umpolung of the Imine Reactivity

“…[1][2][3] The problem Ϫ although early recognized [4] Ϫ was investigated much later and owes the start of its vigorous research to Corey and Seebach in the mid 1960s. [5] Seebach subdivided the methods of the nucleophilic acylation into three categories ( Figure 1): [6,7] unprotected acyl or acyl-analogous derivatives 1, vinyl ether type protected acyl anions 2, and acetal-type protected compounds 3.…”

The Catalyzed Desulfinylative Allylation of Carbonyl Compounds with Alk‐2‐enesulfonyl Chlorides and Silyl Alk‐2‐enesulfinates

“…[19] Alternative mechanisms implying radical intermediates [20] and oxidation/reduction equilibria (OppenauerMeerwein-Ponndorf-Verley-type mechanism) have been proposed. [21] These alternative mechanisms suggested to us that CrCl 2 might induce desulfinylation of alk-2-enesulfonyl chlorides generating allylchromiumA C H T U N G T R E N N U N G (III) intermediates that could be used as nucleophilic partners in carbonyl-compound allylation, thus creating umpolung [22] reactivity by converting allyl-SO 2 Cl compounds (C-electrophile) into allyl-metal compounds (C-nucleophile; Scheme 2).…”