Sodium triacetoxyborohydride

Description

Sodium triacetoxyborohydride (STAB) is a mild reducing agent that is commonly used in reductive aminations. STAB has the advantage over sodium cyanoborohydride (NaBH3CN) of not producing toxic side-pdts. One disadvantage of STAB is that it is H2O sensitive, not compatible with MeOH, and reacts slowly with EtOH and isopropanol. For these reasons STAB is typically used with aprotic solvents such as DCE, DCM, THF, dioxane, or toluene.

Chemical properties

Sodium triacetoxyborohydride (STAB-H) is commercially available as a hygroscopic white powder with a melting point of 116-120 °C. freely soluble in benzene. It is prepared by the reaction of NaBH4 with excess acetic acid in benzene or toluene.

The Uses of Sodium triacetoxyborohydride

Sodium Triacetoxyborohydride(STAB) is a hydride reagent used in stereoselective reductive amination. It is able to replace toxic sodium cyanoborohydride under most conditions. It is selective in reducing aldehydes to alcohols in the presence of ketones. STAB is also stable in anhydrous acids, which enables reductive amination of aldehydes and ketones. It used in reductive amination of ketones and aldehydes and reductive amination/lactamization of carbonyl compounds with amines. The advantage of STAB compared to sodium cyanoborohydride is evident. STAB, being non-toxic, is easier to handle and forms no toxic by-products, making the treatment of process waste after the reaction simple and less costly.

The Uses of Sodium triacetoxyborohydride

A slurry of the amine (50 mg, 0.12 mmol) and the aldehyde (31.6 mg, 0.18 mmol) in 1,4-Dioxane (3 mL) was stirred for 5 min then treated with NaBH(OAc)3 (77 mg, 0.363 mmol). After stirring 10 min, DCM was added to the reaction mixture. The resulting solution was washed with saturated aq NaHCO3, water, and brine. The organics were dried (MgSO4) and concentrated in vacuo to provide the product which was used in the next step without further purification.

What are the applications of Application

Sodium triacetoxyborohydride is a reagent used for reductive amination of carbonyl compounds with amines

What are the applications of Application

Sodium triacetoxyborohydride is a mild reagent that exhibits remarkable selectivity as a reducing agent. It reduces aldehydes but not ketones; however, beta-hydroxyketones can be reduced selectively to give 1,3-trans diols.The steric and the electron-withdrawing effects of the three acetoxy groups stabilize the boron-hydrogen bond and are responsible for its mild reducing properties.
Sodium triacetoxyborohydride or [NaBH(OAc)3] can be used as a reagent:
In the reductive amination of ketones and aldehydes.
To prepare N-benzyl-γ-valerolactam by reacting with methyl 4-oxopentanoate and benzylamine via reductive amination/lactamization.
To reduce imines and enamines to corresponding amines.
To reduce quinolines and isoquinolines to corresponding tetrahydro derivatives.
In the hydroboration of alkenes.
To synthesize nitroxide biradicals for creating high relaxivity terminal groups linkage to dendrimers.

Reactions

Sodium Triacetoxyborohydride is selective reducing agent in organic synthesis. It is especially suitable for reductive aminations. Since the reaction rate for the reduction of iminium ions is much faster than for ketones or even aldehydes, the reductive amination can be carried out as a one-pot procedure by introducing the reducing agent into a mixture of the amine and carbonyl compound. The presence of a stoichiometric amount of acetic acid, which catalyzes the imine formation and provides the iminium ion, doesn't present any problem under these conditions.

Reductive amination (simplified)

Preparation

Sodium triacetoxyborohydride can be prepared by protonolysis of sodium borohydride with acetic acid:
NaBH4 + 3 HO2CCH3 → NaBH(O2CCH3)3 + 3 H.