Butanolide und Butenolide durch intramolekulare En-Reaktion bei der Thermolyse von Propargyl-propiolaten
| Autor: | Martin Karpf, Vanda Bilinski, André S. Dreiding |
|---|---|
| Rok vydání: | 1986 |
| Předmět: |
chemistry.chemical_classification
Bicyclic molecule Double bond Intramolecular reaction Stereochemistry Dimer Organic Chemistry Regioselectivity Biochemistry Catalysis Inorganic Chemistry chemistry.chemical_compound chemistry Intramolecular force Drug Discovery Propargyl Physical and Theoretical Chemistry Ene reaction |
| Zdroj: | Helvetica Chimica Acta. 69:1734-1741 |
| ISSN: | 1522-2675 0018-019X |
| DOI: | 10.1002/hlca.19860690730 |
| Popis: | Butanolides and Butenolides by Intramolecular Ene-Reaction during Thermolysis of Propargyl Propiolates Gas-phase flow thermolysis of 2-butynyl propynoate (1) and 2-propynyl 2-butynoate (2) at 550° afforded 3-ethynyl-2-methyl-2-buten-4-olide (4, 85%) and 2-ethynyl-3-methyl-2-buten-4-olide (5, 80%), respectively. Their formation presumably entails an ene reaction between the methylacetylenic and the acetylenic functions of the diyne esters 1 and 2 to give the two methyliden-vinyliden-butanolides 10 and 11 as intermediates, followed by a [1,5]-H shift to 4 and 5. At 400–450°, the gas phase flow thermolysis of 1 and 2 led to the dimers 16 (77%) and 17 (6%), respectively. These products resulted from the Diels-Alder dimerization of the above mentioned intermediates 10 and 11. The regioselectivity of this dimerization is determined by a ‘head-to-head’ approach, with the double bond conjugated to the carbonyl group acting as the dienophile in both cases. The low yield of 17 from 2 is probably due to a further Diels-Alder reaction of the dimer 17 with its precursor 11, yielding a trimer 18 (8% isolated). This process is not possible when starting with 1, which explains the higher yield of 16. The gas phase flow thermolysis of 2-butynyl 2-butynoate (3) at 550° afforded a mixture of four isomeric products, namely the two monocyclic ethynyl-butenolides 6 and 7 and the two bicyclic vinyl-butenolides 8 and 9. The formations of 6–9 are also rationalizable by initial ene-reactions, in this case two alternative ones, each involving one of the two CH3 groups of 3. This leads to two alkylidene-vinylidene-butenolides, namely 12 and 13. A [1,5]-H shift converts 12 into 6 and 13 into 7. A competing alternative [1,5]-H shift transforms both 12 and 13 to the triene 14, which electrocyclizes to the cyclohexadiene 15. The latter undergoes two alternative [1,5]-H shifts to yield 8 and 9. |
| Databáze: | OpenAIRE |
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