ISSN:
0170-2041
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Description / Table of Contents:
De-novo Synthesis of Carbohydrates and Related Natural Products, 18. - Hetero-Diels-Alder Reactions for the Synthesis of 3,4-Dihydro-2H-pyransHetero-Diels-Alder reactions between α,β-unsaturated carbonyl compounds with functional substituents in α- and β-position and enol ethers, enediol ethers, and ketene acetals, respectively, result in the formation of 3,4-dihydro-2H-pyrans 3, having functional substituents partially in all ring positions. Especially useful are β-acyloxy-α-phenylthio-substituted heterodienes yielding preferentially the endo-products (≥ 10:1). Reaction of 5-acyl-and 5-carboxyl-substituted compounds with lithium tri(sec-butyl)hydroborate (L-Selectride) and diisobutylaminium hydride (DIBAH), respectively, gives via reduction the corresponding 5-hydroxyalkyl-substituted derivatives 5. 1H NMR spectral data support the preference of the 2H3-conformer for 2,4-di-O-substituted 3,4-dihydro-2H-pyrans.
Notes:
Hetero-Diels-Alder-Reaktionen zwischen α,β-ungesättigten Carbonylverbindungen mit funktionellen Substituenten in α- und β-Position und Enolethern, Endiolethern oder Ketenacetalen führen zu 3,4-Dihydro-2H-pyranen 3, die teils in allen Ringpositionen funktionelle Substituenten aufweisen. Besonders bewährt haben sich β-Acyloxy-α-phenylthio-substituierte Heterodiene, die bevorzugt endo-Addukte (≥ 10:1) liefern. Umsetzung von 5-Acyl-und 5-Carboxy-substituierten Vertretern mit Lithium-tri(sec-butyl)hydroborat (L-Selectrid) bzw. Diisobutylaluminiumhydrd (DIBAH) führt unter Reduktion zu 5-Hydroxyalkyl-Derivaten 5. 1H-NMR-Daten belegen die Bevorzugung der 2H3-Konformation für 2,4-di-O-substituierte 3,4-Dihydro-2H-pyrane.
Additional Material:
5 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jlac.198519851116
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