The major reducing species operative when an equimolar proportion of AlCl₃ is added over a short period of time to an ether solution of equimolar proportions of LiAlH₄ and acetal or ketal

Abstract

The relative ease of hydrogenolysis of ether solutions of acetals or ketals is much greater with AlHzCl than with AlH3. Conversion of the species AlHs & AlHzCl P AlHClz one into the other is fast, and is accomplished by the addition of the appropriate quantity of AlC13 or LiAIH4 to solutions of HlH8 or AlHC12, respectively. Gradual addition of an equimolar proportion of AlCla in ether to an ether solution of equimolar roportions of LiAlH4 and acetal or ketal first forms AlHa, which is rapidly converted into & H~C I as more AlCl3 is added. During the time of this addition (210 min) little reduction by AlH3 takes place. Most of the reduction is done by the species AlHzCl when the AlCl3 is completely added.

The Influence of the 2-Alkoxy Group and of C-5 Substituents on the Direction of Reductive Cleavage of 2-Alkoxytetrahydrofurans by AlH2Cl in Ether Solution

“…They concluded from this that the steric effect of the C-2 alkoxy group was more important than was the basicity of the ring oxygen in directing the course of reductive cleavage. The discrepancy between our results and those reported (12) might be due to the fact that we employed as reducing system a 1 : 1 mixture of AlCl, and LiAlH, which provides AlH,Cl (2,3) whereas Eliel et al (1 2) used a 4: 1 mixture of AlCl, and LiAlH,, which provides a 1 : 4 mixture of AlC1, and AlHCl, (2,3). This view is supported by the data in Table 2 which show the results of the hydrogenolysis of 2-benzyloxytetrahydrofuran by the series of reagents AlH,, AlH,Cl, AlHCl,, and the 4: 1 mixture of AlHC1, with AlCl, (Eliel's reagent).…”

Kinetics and Mechanism of Polymerization of n-Butyl Vinyl Ether Initiated by Dichloroalane (AlHCl2): A New Cationic Initiating System

“…The reaction between lithium aluminum hydride and aluminum(III) chloride was investigated in details by Ahsby and Prather, and according to their results in this reaction alane (AlH 3 ), chloroalane (AlH 2 Cl) and dichloroalane (AlHCl 2 ) are formed depending upon the molar ratio of the reagents: The halogen alanes exist as monomers in ethers and do not form polimers. , The Lewis acidic strength of the mixed hydrides and AlCl 3 increases as shown below because of the high electronegativity of the chlorine atom: On the other hand, the hydrogen donating ability of these species decrease in this order.…”

A Highly Stereoselective Approach to the Synthesis of Functionalized Pyran Derivatives by Lewis Acid Assisted Ketal Reduction and Allylation

“…In this vein, alane-type reagents were explored. Literature precedent for using alane as a ketal reducing agent involves the generation of the reagent in situ from alumnium chloride (AlCl 3 ) and lithium aluminum hydride (LiAlH 4 ) in diethyl ether. ,,,− Nonstoichiometric ratios of AlCl 3 and LiAlH 4 provide chloroalane reagents. A summary of the results obtained from reductive cleavage of ketal 1 with LiAlH 4 /AlCl 3 mixtures is provided in Table .…”