Synthesis and isomerization of enyne-group containing compounds in NaEDA/EDA media

A series of conjugated enyne-group and isolated triple bond containing compounds were synthesized and their behavior in superbasic media NaEDA/EDA studied


Introduction
The multipositional migration of the triple bond along the carbon chain in hydrocarbons and alcohols by potassium 3-aminopropanamide was introduced by Brown 1 .Later other superbasic systems based on different alkali metal amides of 1,2-diaminoethane and 1,3-diaminopropane for such processes were developed [2][3][4][5] .The triple bond usually migrates to the terminal position of carbon chain but in branched chain compounds 6 and carboxylic acids 7,8 , several other compounds have been obtained.Remissive ET al. 9,10 have described the successful migration of conjugated diyne group in hydrocarbons and alcohols with LiEDA/EDA.The conjugated enyne group was still isomerized only at 1-position in (Z, E)-2-hexen-3-yn-1-ol by influence of KNH 2 /NH 3 11 .The lack of the data on multipositional isomerization of enyne-group inspired us to investigate this type of reaction on different model compounds to show the scope and limitations of this transformation.
It appears that the order of double and triple bond with respect of the functional group in enynol also influences the isomerization.Thus, the position of enyne group in (Z, E)-4-octen-2yn-1-ol ( 4 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 NaNH 2 /NH 3 13 .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 formed 13 .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.
All isomerization experiments were done under dry and oxygen-free Ar-atmosphere.Ar was passed through the column (2.5*23 cm) with Ni (CrO 2 ) 2 granulated catalyst as oxygen bonding agent and through the column (4*18 cm) with molecular sieves 4Å to remove H 2 O and CO 2 .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.
General Procedures.To a dry stirred EDA (3 mL) under Ar-atmosphere NaNH 2 (0.195g, 0.005 mol) was added and the mixture was stirred at room temperature until the gray colour changed to violet (0.5 h).The compound studied (0.001 mol) was added to 1.7M NaEDA/EDA solution.
The stirring was continued and the reaction was monitored by GLC.When reaction was over, the mixture was hydrolyzed by ice water, extracted with ether and washed first with the 10% HCl solution, then with the saturated solutions of NaHCO