Abstract: Tetrabutylammonium cyanoborohydride or the combination of nabh sodium cyanoborohydride with Aliquat 336 provides useful, convenient reagents for reductive amination of aldehydes nabh and ketones in aprotic or protic media.
JOC, (1977 42,.
With these in mind, you can correctly assume that LiBH4 is reduction intermediate between LiAlH4 and NaBH4 nabh as far as strength of reducing agent is concerned).(6 other reagent systems recently introduced for reductive amination include: (a)potassium hydridotetracarbonylferrate, Bodrini,.P.; Panunzio,.; Umani-Ronchi,.Two limitations reduction were encountered. .So what does methanol do in this reaction/what imine is the effect of methanol?Versatile, Selective Reagents for Reductive Aminations in Nonpolar Media.Approximately 1g of 4A molecular sieves was added (to absorb water formed and the mixture was stirred at imine ambient temperature. .One can look both at the metal and the hydride source. This means that the imine initial activation of livre the carbonyl in a reduction by the metal happens more effectively with lithium.
Jacs, (1973 95, 6131; a number of other tetraalkylammonium cyanoborohydrides are also readily available: Reparasky,.E.; Weidig,.; Kelly,.C.
Examples using the standard method (sodium cyanoborohydride, methanol, 2-3days)2 are included for comparisons. .
Phase transfer was also used to solubilize sodium cyanoborohydride by employing Aliquat 336, an inexpensive liquid reagent composed of methyltrialkylammonium chlorides with C8-C10 chains. .First, let's look at the hydride source.This is because aluminum is less electronegative than boron, and thus the electron density is shifted more towards the hydrogen in mathAlH_4-/math compared to mathBH_4-/math.(4) Hutchins,.O.; Rotstein,.; Natale,.R.; Fanelli,.; Dimmel,.Recently, the intermediacy of iminium ions in certain reductive aminations has been questioned: Tadanier,.; petmeds Hallas,.; Martin,.R.; Stanaszek,.S.To circumvent the solubility problem imine and hence augment the utility of cyanoborohydride, we have explored the use of the tetrabutylammonium derivative9 and other phase-transfer techniques10 for typical cyanoborohydride reductions in nonpolar media.5,9,11 This communication reports the successful application of phase transfer to reductive amination, which.In such cases, methanol solvent is clearly superior.2.(e) ion-exchange resin supported BH3CN-, Hutchins,.O.; Natale,.R.; Taffer,.M.To a solution containing nabh pyrrolidine (4.26g, 60mmol) in 21ml of DCM was added HCl (20mmol, 8ml nabh of.5N solution in methanol) nabh followed by cyclohexanone (0.98g, 10mmol sodium cyanoborohydide (0.44g, 7mmol and Aliquat 336 (2.93g, 7mmol). .JOC, (1976 41, 3328.Relatively hindered secondary amines (i.e., diethylamine) reacted only reluctantly with ketones and gave inferior yields ( 40) of amine products. .Progress of the reactions could be followed by monitoring the disappearance of the carbonyl. .My question is what is the function of methanol in this reaction as methanol reacts with NaBH4 to form sodiumtetramethoxyborate and hydrogen gas.
The results for a range of carbonyls and amines are presented in Table. .
General Reaction Procedure: The general reaction procedure is nabh illustrated for the preparation of N-cyclohexylpyrrolidine. .
Compendium of Phase-Transfer Reactions and Related Synthetic Methods; Fluka AG, Ch-9470 Buchs, Switzerland, (1979).