The Number of Hydride Ions in AlH₂Cl Available for Hydrogenolysis of 1,3-Dioxolanes

Abstract

2-Methyl-l,3-dioxolane (1) in ether is hydrogenolyzed completely to 2-ethoxyethanol by an equimolar proportion of AIH,CI, whereas a 112 mol of AIH2CI hydrogenolyzes 1 mol of 1 only to the extent of 50%. In the latter case, the intermediate compound 2-ethoxyethoxyhydridoaluminum chloride (CzHSOCH2-CH20AIHCI) formed with half of the 2-methyl-1,3-dioxolane, even though it contains a hydride ion, fails to react with the remainder of the dioxolane. This is believed due to the preference of C,HsOCH2-CH20AIHCI to form an internal Lewis acid-base complex rather than form a similar complex with 1, a step essential to facilitate the hydrogenolysis of 1.La reaction dans I'kther entre le mkthyl-2 dioxolane-1,3 (1) et une proportion molaue de AlH,CI conduit ti I'kthoxy-2 kthanol provenant d'une hydrogknolyse complete; par ailleurs I'action d'une demimole de AlH2Cl sur une mole de 1 conduit ti une hydrogknolyse de 50% de ce composk. Dans ce cas, le composk intermkdiaire (C2HsOCH2CH20AIHC1) fomk avec la moitiC du dioxolane 1 contient encore un ion hydrure mais il ne rkagit toutefois pas avec le restant du dioxolane. On croit que ce phknomene est du ti la prkfkrence de I'intermkdiaire ti former un complexe de Lewis interne plut6t que de former avec 1 un complexe semblable qui est essentiel pour faciliter I'hydrogknolyse de 1.Canadian Journal of Chemistry, 49. 2166Chemistry, 49. (1971 In connection with a study of the LiAlH,-of epoxides by the mixed hydride (3, 4) and AlCl, (mixed hydride) reductive cleavage of alkoxyaluminum hydrides have been prepared 1,3-dioxolanes in this laboratory, we have found and used to hydrogenolyze epoxides (5), it apthat 2-methyl-l,3-dioxolane (1, Scheme 1) is con-pears from our work that 3 cannot hydrogenolyze verted completely to 2-ethoxyethanol 4 in less 1. That this is so has been shown by the failure to than 30 min by an equimolar proportion of di-observe any reductive cleavage when an ether hydridoaluminum chloride, AlH2C1.2 However, solution of 1 was treated for as long as 48 h with no more than 50% conversion of 1 to 4 could be 3, prepared separately by the reaction of A1H2C1 obtained if a h a y molar proportion of AlH2C1 with an equimolar amount of 2-ethoxyethanol was used, even if the reaction time was extended according to directions (5) which describe the to 48 h. In accordance with the views concerning preparation of alkoxyaluminum hydrides. the course of the reductive cleavage of 1,3-di-The complete conversion of benzaldehyde to oxolanes (1, 2), the reaction of A1H2C1 with 1 benzyl alcohol by 3 in less than 1 h shows that the first involves formation of a complex 2 due to the single hydride unit in 3 is available for reduction Lewis acidity of AlH2Cl, and this complex subse-of carbonyl compounds and it is not the bulk of quently forms an alkoxyhydridoaluminum chlor-reagent 3 which causes its failure to react with 1. ide 3 (Scheme I).Furthermore, we have also shown that 1 is conAlthough alkoxyaluminum hydrides have been verted to 2-ethoxyethanol 4 in less than 30 min postulated as int...

Synthesis of 2-substituted tetrahydroisoquinolin-6-ols: potential scaffolds for estrogen receptor modulation and/or microtubule degradation

“…13 General procedure for the reduction of the acetamides 33. 49,50 To a suspension of AlH2Cl made by adding AlCl3 (140 mg, 1.06 mmol) to a stirred suspension of LiAlH4 (41.0 mg, 1.08 mmol) in anhydrous THF (30 mL) at −3 o C in small portions followed by stirring at 24 o C for 30 min, was added the amides (0.713 mmol) in THF (4.0 mL). The reaction mixture was then stirred under reflux for 5 h, cooled to 24 o C and carefully treated with water until no further effervescence occurred.…”