[59211-98-2] · C10H21AlO2 · Diethyl-t-butoxycarbonylmethylaluminum · (MW 200.26)
Preparative Method: prepared in situ from t-butyl lithioacetate (Rathke's salt)2 and Diethylaluminum Chloride in toluene at -40 °C (eq 1). Instantaneous deposition of lithium chloride is observed and the resulting suspension is used directly in reactions with epoxides.1 Other solvents, such as THF and DME, are also used successfully.3
Handling, Storage, and Precautions: the reagent should be used without isolation immediately after preparation. Reactions must be performed under an inert atmosphere (N2, Ar).
Reaction of diethyl-t-butoxycarbonylmethylaluminum with cyclohexene oxide at ambient temperature gives the trans-g-hydroxy ester, which in turn can be converted into a trans-g-lactone (eq 2). In contrast, the reaction of cyclohexene oxide and t-butyl lithioacetate gives the hydroxy ester in very poor yield (eq 3).1
Ring opening reactions of sterically hindered epoxides, however, are not successful with this aluminum reagent in toluene (eq 4).
Regio- and stereospecific opening reactions of unsymmetrical epoxides may be carried out under various conditions. The reactions are much faster in THF and DME than in toluene, and the yields of hydroxy esters are also greatly improved (eqs 5 and 6).3 Remarkably, the reactions of allylic epoxides proceed by direct SN2 pathways (eq 5).
The University of Tokyo, Japan