Abstract:The lead tetraacetate oxidation of the optically active aliphatic alcohol 1 in benzene afforded the tetrahydrofurane derivative 3 and the 3‐acetoxy‐tetrahydro‐pyranes 4–6 as major products. The formation of the expected compound 3 in racemic form is interpreted by the stepwise sequence a → b → c → d1–3 → e. The appearance of a carbonium ion of type d3 in the conversion 1 → 3 is in contrast to the direct oxydative ring closure (cf. c → e) which had been postulated previously for cases involving alicyclic educts… Show more
“…Acetoxytetrahydrofuran 3z was isolated as the major product (20%), and the starting alcohol was detected (33%) (eq 5). Both rapid oxidation of the generated tertiary radical to lead to an olefin and rapid decarbonylation of the tertiary acyl radical conspire to prevent carbonylation of this substrate. Further oxidation of the resultant alkenyl alcohol consumed LTA to give the THF derivative 3z and the recovered 1z (Scheme ). , 4 5 …”
Section: Limitations and Prospects For The Lta-free Systemmentioning
This paper describes the δ-carbonylation of saturated alcohols which uses a 1,5-hydrogen-transfer reaction of alkoxyl radicals and subsequent carbonylation at the δ-carbon atoms as the key. The carbonylation reactions of five classes of saturated alcohols, namely, primary alcohols having primary δ-carbons, primary alcohols having secondary δ-carbons, primary alcohols having tertiary δ-carbons, secondary alcohols having primary δ-carbons, secondary alcohols having secondary δ-carbons, were carried out, in which lead tetraacetate (LTA) was used as a one-electron oxidant to generate the alkoxyl radicals. Carbonylation of these saturated alcohols, except for primary alcohols having tertiary δ-carbons, took place to afford δ-lactones in moderate to good yields. The mechanism of the remote carbonylation likely involves (1) alkoxyl radical generation via LTA oxidation of a saturated alcohol, (2) conversion of this alkoxyl radical to a δ-hydroxyalkyl radical by a 1,5-hydrogen-transfer reaction, (3) CO trapping of the δ-hydroxyalkyl radical yielding an acyl radical, and (4) oxidation and cyclization of the acyl radical to give a δ-lactone. A metal salt-free system was also tested for a substrate derived from a tertiary alcohol having a secondary δ-carbon; the photolysis of an alkyl 4-nitrobenzenesulfenate under CO pressures gave a δ-lactone in moderate yield.
“…Acetoxytetrahydrofuran 3z was isolated as the major product (20%), and the starting alcohol was detected (33%) (eq 5). Both rapid oxidation of the generated tertiary radical to lead to an olefin and rapid decarbonylation of the tertiary acyl radical conspire to prevent carbonylation of this substrate. Further oxidation of the resultant alkenyl alcohol consumed LTA to give the THF derivative 3z and the recovered 1z (Scheme ). , 4 5 …”
Section: Limitations and Prospects For The Lta-free Systemmentioning
This paper describes the δ-carbonylation of saturated alcohols which uses a 1,5-hydrogen-transfer reaction of alkoxyl radicals and subsequent carbonylation at the δ-carbon atoms as the key. The carbonylation reactions of five classes of saturated alcohols, namely, primary alcohols having primary δ-carbons, primary alcohols having secondary δ-carbons, primary alcohols having tertiary δ-carbons, secondary alcohols having primary δ-carbons, secondary alcohols having secondary δ-carbons, were carried out, in which lead tetraacetate (LTA) was used as a one-electron oxidant to generate the alkoxyl radicals. Carbonylation of these saturated alcohols, except for primary alcohols having tertiary δ-carbons, took place to afford δ-lactones in moderate to good yields. The mechanism of the remote carbonylation likely involves (1) alkoxyl radical generation via LTA oxidation of a saturated alcohol, (2) conversion of this alkoxyl radical to a δ-hydroxyalkyl radical by a 1,5-hydrogen-transfer reaction, (3) CO trapping of the δ-hydroxyalkyl radical yielding an acyl radical, and (4) oxidation and cyclization of the acyl radical to give a δ-lactone. A metal salt-free system was also tested for a substrate derived from a tertiary alcohol having a secondary δ-carbon; the photolysis of an alkyl 4-nitrobenzenesulfenate under CO pressures gave a δ-lactone in moderate yield.
Uei der Oxydation einwertiger Alkohole mit Blei(1V)-acetat findet man je nach dem verwendeten Ausgangsstoff als Reaktionsprodukte Tetrahydrofuranderivate [412), durch Dehydrierung der Carbinolgruppe gebildete Carbonylverbindungen [S] [6] oder Fragmentierungsprodukte. Die letzteren entstehen aus den primar sich bildenden Bleitriacetoxy-alkoholaten (vgl. a) durch Spaltung der cc, ,&Bindung und Ausbildung eines Kohlenstoffradikals (b) und einer Carbonylgruppe (c) [6-lo]. C,-0-Pb(OAc), -+ -& + b = O + -Pb(OAc), Fur die intramolekulare Atherbildung miissen bestimmte sterische Voraussetzungen erfiillt sein, damit diese zur Hauptreaktion wird (vgl. die Ubersicht in [ll]). Anderseits l a s t sich die Oxydation sekundarer Alkohole und primarer aromatischer Carbinole zu Ketonen bzw. Aldehyden durch Basen katalysieren [12]. Die Faktoren, welche die Geschwindigkeit der Fragmentierungsreaktion beeinflussen, sind kiirzlich ebenfalls diskutiert worden [7, 8, 111. Obwohl kinetische Messungen bei Blei(1V)-I 4 Is-[ I I a b c 1) 205. Mitteilung der Reihe nUber Steroideo ,(204. Mitt.: [l]) sowie 230. Mitteilung der Reihe D Steroide und Sexualhormoner (229. Mitt. : [Z]) und gleichzeitig 10. Mitteilung iiber (( Oxydationeii einwertiger Alkoholc mit Blei(1V)-acetat )) (9. Mitt. : [29]). 8) Dic Zahlcn in eckigen Klammern verweiscn auf das Literaturverzeichnis, S. 1978.
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