Borane dimethyl sulfide

The desired pyridylamine was obtained in 69 % overall yield by monomethylation of 2-(aminomethyl)pyridine following a literature procedure (Scheme 4.14). First amine 4.48 was converted into formamide 4.49, through reaction with the in situ prepared mixed anhydride of acetic acid and formic acid. Reduction of 4.49 with borane dimethyl sulfide complex produced diamine 4.50. This compound could be used successfully in the Mannich reaction with 4.39, affording crude 4.51 in 92 % yield (Scheme 4.15). Analogous to 4.44, 4.51 also coordinates to copper(II) in water, as indicated by a shift of the UV-absorption maximum from 296 nm to 308 nm. 

Pyridyl)hydrazine (Aldrich), 4-acetylpyridine (Acros), N,N,N -trimethylethylenediamine (Aldrich), methylrhenium trioxide (Aldrich), InQj (Aldrich), Cu(N0j)2-3H20 (Merck), Ni(N03)2-6Il20 (Merck), Yb(OTf)3(Fluka), Sc(OTf)3 (Fluka), 2-(aminomethyl)pyridine (Acros), benzylideneacetone (Aldrich), and chalcone (Aldrich) were of the highest purity available. Borane dimethyl sulfide (2M solution in THE) was obtained from Aldrich. Methyl vinyl ketone was distilled prior to use. Cyclopentadiene was prepared from its dimer immediately before use. (R)-l-acetyl-5-isopropoxy-3-pyrrolin-2-one (4.15) has been kindly provided by Prof H. Hiemstra (University of Amsterdam). 

Diborane [19287-45-7] the first hydroborating agent studied, reacts sluggishly with olefins in the gas phase (14,15). In the presence of weak Lewis bases, eg, ethers and sulfides, it undergoes rapid reaction at room temperature or even below 0°C (16—18). The catalytic effect of these compounds on the hydroboration reaction is attributed to the formation of monomeric borane complexes from the borane dimer, eg, borane-tetrahydrofuran [14044-65-6] (1) or borane—dimethyl sulfide [13292-87-0] (2) (19—21). Stronger complexes formed by amines react with olefins at elevated temperatures (22—24). 

Borane—dimethyl sulfide complex (BMS) (2) is free of these inconveniences. The complex is a pure 1 1 adduct, ca 10 Af in BH, stable indefinitely at room temperature and soluble in ethers, dichioromethane, benzene, and other solvents (56,57). Its disadvantage is the unpleasant smell of dimethyl sulfide, which is volatile and water insoluble. Borane—1,4-thioxane complex (3), which is also a pure 1 1 adduct, ca 8 Af in BH, shows solubiUty characteristics similar to BMS (58). 1,4-Thioxane [15980-15-1] is slightly soluble in water and can be separated from the hydroboration products by extraction into water. 

Monohalogenoboranes are conveniendy prepared from borane—dimethyl sulfide and boron trihahdes (BX where X = Cl, Br, I) by redistribution reaction, eg, for monochloroborane—dimethyl sulfide [63348-81-2] (9) (81—83). Other methods are also known (84—87). 

Dihalogenoboranes are conveniently prepared by the redistribution of borane—dimethyl sulfide with boron trihaUde—dimethyl sulfide complexes (82,83), eg, for dibromoborane—dimethyl sulfide [55671-55-1] (14). 

Among chiral dialkylboranes, diisopinocampheylborane (8) is the most important and best-studied asymmetric hydroborating agent. It is obtained in both enantiomeric forms from naturally occurring a-pinene. Several procedures for its synthesis have been developed (151—153). The most convenient one, providing product of essentially 100% ee, involves the hydroboration of a-pinene with borane—dimethyl sulfide in tetrahydrofuran (154). Other chiral dialkylboranes derived from terpenes, eg, 2- and 3-carene (155), limonene (156), and longifolene (157,158), can also be prepared by controlled hydroboration. A more tedious approach to chiral dialkylboranes is based on the resolution of racemates. /n j -2,5-Dimethylborolane, which shows excellent enantioselectivity in the hydroboration of all principal classes of prochiral alkenes except 1,1-disubstituted terminal double bonds, has been... 

The oxazaborolidines are easily prepared by heating ephedrine with borane dimethyl sulfide or the appropriate boronate ester. The aluminum reagent C is obtained by mixing ephedrine and trimethylaluminum. Borolidinc A is superior to its methyl derivative B and to the aluminum analog C. The diastereomeric borolidine obtained from borane and (S,S)-pseu-doephedrine failed to show any cnantioselectivity25. A variety of aromatic aldehydes can be enantioselectively alkylated in the presence of A, however, with heptanal the enantioselectivity is poor25. 

Scheme 17 Reduction of nitriles using borane dimethyl sulfide and microwave irradiation...

The kinetics of the reaction was measured by NMR studies and the reaction was found to be first order relative to borane-dimethyl sulfide and to the substrate (Figure 5.3). This result was consistent with a bimolecular reaction in the rate-limiting step. 

Primary amino methylene substituents were introduced by a sequence of cya-nodehalogenation and subsequent reduction of the resulting nitrile with borane dimethyl sulfide. To incorporate tertiary aminomethylene substituents into the 2-pyri-done framework, a microwave-assisted Mannich reaction using preformed iminium salts proved to be effective. 

Borane dimethyl sulfide complex 2 M solution in tetrahydrofuran, 0.5 mL, 1 mmol, 1 eq... 

After being stirred for 2 hours at room temperature, 10 M borane-dimethyl-sulfide complex (2.0 mL) was added. The mixture was heated under reflux for 65 hours. The resulting mixture was cooled to room temperature and cautiously transferred into 2N hydrochloric acid (10 mL) in a 200 mL round-bottomed flask equipped with a magnetic stirrer bar using diethyl ether (10 mL). 

In a 250 mL round-bottomed flask with an argon inlet equipped with a magnetic stirring bar the CBS-catalyst (1.85 g) was dissolved in tetrahydrofuran (10 mL) and cooled to 0°C in an ice bath. From a syringe filled with borane dimethyl sulfide-complex (2.00 mL dissolved in 10 mL THF) 20% of the volume (2.40 mL) were added and the solution was stirred for 5 minutes. A solution of the diketone (3.00 g dissolved in 30 mL THF) was added from a second syringe simultaneously with the rest of the borane dimethyl sulfide-complex over 2 hours. The resulting yellow solution was stirred for another... 

First-order kinetics have been found for the reductions of pinacolone by borane-dimethyl sulfide in THF, which proceeds via a monoalkoxyborane complex. In contrast, the kinetics were second order for the reduction with catecholborane and the reactive species was found to be a catecholborane dimer present in small concentrations. 

The chemistry and procedures for modification of the - CO2H groups of PAA hyperbranched grafts on PE powder were analogous to those used for PAA grafts on PE or PP films and wafers. For example, a 90% yield in ester formation was possible using acid-catalyzed Fisher esterification. Likewise, quantitative reduction (ethyl chloroformate activation, borane-dimethyl sulfide reduction) to hyperbranched poly(allyl alcohol)s and amidation all could be carried out using procedures like those used for PAA/Au surfaces. 

The reaction with 4-nitrophenol activated by 5-ethylthio-l-ff-tetrazole led to formation of the 4-nitrophenyl phosphite (step a). Among several boronating reagents tested borane-dimethyl sulfide gave the optimal yield of... 

A solution of borane in tetrahydrofuran reduces esters at room temperature only slowly [977]. Under such conditions free carboxylic groups of acids are reduced preferentially monoethyl ester of adipic acid treated with 1 mol of borane in tetrahydrofuran at — 18° to 25° gave 88% yield of ethyl 6-hydroxy-hexanoate [977]. Borane-dimethyl sulfide in tetrahydrofuran was used for... 

Yields sometimes drop when an old bottle of borane-dimethyl sulfide is used. Reaction progress can be monitored by thin layer chromatography (silica gel, eluting with 10 10 1 chloroform-methanol-concentrated ammonium hydroxide). Any remaining phenylalanine stains heavily when exposed to ninhydrin (Rf 0.35). If phenylalanine is detected after 5 hr of reflux, an additional 10 ml (0.10 mol) of borane-dimethyl sulfide is added via syringe, and the solution is heated at reflux for 1 additional hr. 

Borane-dimethyl sulfide (10 M) was purchased from Aldrich Chemical Company, Inc. and used as received. 

Cyclohexene was purchased from Wako Pure Chemical Ltd. Japan, or Aldrich Chemical Company, Inc., and used after distillation from lithium aluminum hydride. Borane-dimethyl sulfide complex was obtained from Aldrich Chemical Company, Inc., and was used as received. Trifluoromethanesulfonic acid was purchased from Wako Pure Chemical Ltd. Japan or Aldrich Chemical Company, Inc., and used without purification. The checkers used a freshly opened ampule of trifluoromethanesulfonic acid for each run. 

Borane- dimethyl sulfide complex Methyl sulfide, compd. with borane (1 1) Borane, compd. with thiobis[methane] (1 1) (13292-87-0)... 

Caution Borane-dimethyl sulfide complex is foul smelling. All operations using dimethyl sulfide must be carried out in a well-ventilated hood. 

R.O. Hutchins u. F. Cistone, Org. Prep. Proced. Int. 13, 225-240 (1981) . .Utility and Application of Borane-Dimethyl Sulfide in Organic Synthesis". 

An alternative access was achieved by alkylation of the a-diphenylphosphino acetaldehyde SAMP hydrazone 95, yielding the hydrazone products 96 in good yields (60-63%) and good diastereomeric excesses (die = 68-71%) as EjZ mixtures, from which the major diastereomer was separated and purified by preparative HPLC. Ozonolysis and in-situ reduction with the borane-dimethyl sulfide complex of the aldehydes generated gave the air-stable borane-protected 2-diphenylphosphino alcohols 97 in good yields (67-83%). Reaction with DABCO afforded the unprotected 2-phosphino alcohols 98 in very good yields (85-91%) and excellent enantiomeric excesses (ee > 96%) (Scheme 1.1.27). 

Borane-dimethyl sulfide comple and Halstead, E. S. Tetrahedron 2001, 57, 9925. 

Enantioselective reduction of jS-keto nitriles to optically active 1,3-amino alcohols has been carried out in one step using an excess of borane-dimethyl sulfide complex as a reductant and a polymer-supported chiral sulfonamide as a catalyst with moderate to high enantioselectivity (Figure 3.11). The facile and enantioselective method to prepare optically active 1,3-amino alcohols has been used to prepare 3-aryloxy-3-arylpropylamine type antidepressant drugs, for example (l )-fluoxetine. 

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