[59212-00-9] · C8H15AlO · Diethylaluminum Ethoxyacetylide · (MW 154.19)
(functionalized alane for the ring opening of epoxides to trans-ethoxyalkynyl alcohols which can be converted to trans-fused g-lactones1-3)
Solubility: sol toluene.
Preparative Method: prepared in situ by treating lithium ethoxyacetylide (generated from the reaction of equimolar amounts of n-Butyllithium and Ethoxyacetylene) with an equivalent amount of Diethylaluminum Chloride in toluene at -40 °C (eq 1).1
Initial studies using cyclohexene oxide and 2,3-epoxy-trans-decalin indicated that ring opening occurs via a trans-diaxial pathway (eqs 2 and 3). The stereochemistry in each case was demonstrated by converting the intermediate trans-ethoxyethynyl alcohols into the trans-g-lactones. This reaction presumably proceeds via the corresponding hydroxy esters (eqs 4 and 5).1
In an extension of this methodology, the epoxide ring opening was investigated in the presence of a neighboring oxygen functionality and a variety of a-hydroxycyclohexene epoxides were reacted with the alane reagent. The resultant trans-ethoxyalkynyl alcohols were converted into the corresponding ethyl esters by treatment with HCl/ethanol, and lactonization was effected with TsOH-benzene to give the trans-g-lactones in 50-60% yield (eq 6).2
The ring opening of the a-oxygenated epoxides by the alane reagent was interpreted as being trans-diaxial in nature, assuming a preferred equatorial conformation of the neighboring oxygen substituent. It was noted that the course of the reaction is mainly dependent upon the stereochemical relationship of the oxy function and the epoxide and, to an insignificant extent, upon whether or not the oxygen was initially in the form of a hydroxyl or a trimethylsilyl ether. In this case, no directing effect of the neighboring oxygen functionality on the alane was observed since the attack occurs trans to the oxygen.
Ciba-Geigy Corporation, Summit, NJ, USA