Issue in Honor of Professor Kalevi Pihlaja ARKIVOC 2001 (iii) 26-32
By using this knowledge, we synthesized the compound (5) (Z/E=47/53) to test the stability of the enynol group and the reactivity of the isolated triple bond in its neighborhood. Unfortunately the product polymerized even using LiEDA/EDA.
Due to the polymerization of 1-butoxy-(Z,E)-2-octen-4-yne (3) (Z/E=50/50), the behavior of simple propargylic ether in NaEDA/EDA was tested. Such ethers are known as starting materials for the preparation of enynes by influence of NaNH2/NH313. In our experiment with NaEDA/EDA, the corresponding (Z, E)-3-hepten-1-yne (11) was obtained with good yield (Z: E=1:2). In order to study the influence of the position of the triple bond with respect of the alloy group, we synthesized 1-butoxy-10-pentadecyne (7). By influence of NaEDA/EDA, two products containing triple bond were obtained as the 1:1 mixture with total yield of 60%. The mixture was separated by column chromatography on silica. One of these products was the terminal enyne (Z/E=50/50) whereas the other was determined as the butoxy derivative with terminal triple bond. According to those results, the triple bond can migrate to the both ends of carbon chain because several positions may be deprotonated and in equilibrium with each other. When the triple bond moves to the alkoxy group, the butanol is eliminated and after the isomerization the compound with the terminal enyne is formed13. Another terminal position for the triple bond migration can be localized at the other end of molecule because of higher acidity of the acetylenic proton.
It has to be concluded that Na and LiEDA/EDA are powerful superbases for the multipositional isomerization of enyne-group in hydrocarbons and alcohols. These superbases are though too strong in the case of some compounds and cause polymerization.
Experimental Section
General Procedures. 1H and 13C NMR spectra were measured with Bruker AC 200P (Spektrospin AG, Switzerland) spectrometer at 200 and 50 MHz, respectively. IR spectra were recorded on Specord M82 Spectrometer (Carl Zeiss, Jena). GLC analyses: Chrom-5 (Laboratorni Pristroje, Praha), glass columns: 2.5*3mm, 20% Carbowax 20M, Chromosorb W/AW-DMCS, 100-120 mesh; 5% PDEAS, Chromosorb W/HP AW-DMCS, 100-120 mesh; and fused silica capillary column, 0.33*24m, SGE, BP10. For thin layer chromatography Silufol UV254 (Chavalier) plates with silica gel were used. Preparative chromatography was carried out on columns packed with 40-63 µm silica gel. Reagents and chemicals were obtained from Aldrich Chemical Company (USA) and from REACHIM (USSR).
All isomerization experiments were done under dry and oxygen-free Ar-atmosphere. Ar was passed through the column (2.5*23 cm) with Ni (CrO2)2 granulated catalyst as oxygen bonding agent and through the column (4*18 cm) with molecular sieves 4Å to remove H2O and CO2. The batch of ethylenediamine (EDA) was distilled first from KOH and then two times above Na under Ar-atmosphere. For every experiment EDA was distilled freshly from Na under argon.
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