Borane-tetrahydrofuran Research Articles

Towards More Chemically Robust Polymer‐Supported Chiral Catalysts: α,α‐Diphenyl‐L‐prolinol Based Catalysts for the Reduction of Prochiral Ketones with Borane.

α,α–Diphenyl-L-prolinol derivatives with para-bromo substituents in either one or both of the phenyl rings are easily bound to crosslinked polystyrene beads containing phenylboronic acid residues by Suzuki couplings. By using extended reaction periods boronic acid residues that do not take part in the couplings are simply lost by hydrolysis. The polymer-supported (PS) α,α–diphenyl-L-prolinols were used to catalyse reductions of several prochiral ketones with borane in tetrahydrofuran at 22 °C. The expected secondary alcohols were obtained in high chemical yields and ees were generally in the range 79–97 %. One PS catalyst was recycled 14 times without loss of stereochemical performance.

3(1,3-Heterazolidin-3-yl-methyl)-1,3-oxazolidines and their reduction with borane–THF

Preparation of bis-heterazolidines bonded by a CH 2, CH 2–S–CH 2 or CH 2SCH 2SCH 2 groups through their nitrogen atoms is reported: 3-(1,3-oxazolidin-3-ylmethyl)-1,3-oxazolidine 1, 3-(4,4-dimethyl-1,3-oxazolidin-3-ylmethyl)-1,3-oxazolidine 2, 3-(1,3-diazolidin-3-ylmethyl)-1,3-diazolidine 3, 3-(1,3-thiazolidin-3-ylmethyl)-1,3-thiazolidine 4, 3-(1,3-thiazolidin-3-ylmethylsulfanylmethyl)-1,3-thiazolidine 5 and 3-(1,3-oxazolidin-3-ylmethylsulfanylmethyl-sulfanylmethyl)-1,3-oxazolidine 6. The solid state structures of 4 and 5 were determined by X-ray diffraction analyses. BH 3–THF reduction reactions of compounds 1– 6 were investigated. N→BH 3 mono- and di-adducts of 1– 6 were prepared and their structures calculated (ab initio 3-21G*).

Stereoselective addition of organotin anions to R-(+)-pulegone: a route to 8-triorganostannylmenthols

A study on the addition of trimethyl-, tri-n-butyl-, triphenyl-, and (-)-menthyldimethyltin lithium to (R)-(+)-pulegone (5) and (E)-benzalcyclohexanone (8) is reported. It was found that the conjugate addition of the organotin anions to 5 lead in the four cases to mixtures of two adducts in good yields (70-80%) and satisfactory diastereomeric excesses, d.e. (60-78%). The additions to 6 took place mostly in satisfactory yields (64-66%), but in very low yield in the case of the addition of (-)menthyldimethyltin lithium (23%); the d.e. were in the range of 36 to 100%. The addition of phenyl lithium in toluene to some of the new stannyl ketones led to the corresponding tertiary alcohols in fair yields (42-63%), and with d.e. of 40-100%. The reduction of some of the stannyl ketones with borane in THF catalyzed by a Corey catalyst gave the corresponding alcohols in ca 60% yield and with d.e. of 65%. Full 1 H-, 13 C-, and 119 Sn-NMR data of the new organotins are given.

Towards more chemically robust polymer-supported chiral catalysts: alpha,alpha-diphenyl-L-prolinol based catalysts for the reduction of prochiral ketones with borane.

alpha,alpha-Diphenyl-L-prolinol derivatives with para-bromo substituents in either one or both of the phenyl rings are easily bound to crosslinked polystyrene beads containing phenylboronic acid residues by Suzuki couplings. By using extended reaction periods boronic acid residues that do not take part in the couplings are simply lost by hydrolysis. The polymer-supported (PS) alpha,alpha-diphenyl-L-prolinols were used to catalyse reductions of several prochiral ketones with borane in tetrahydrofuran at 22 degrees C. The expected secondary alcohols were obtained in high chemical yields and ees were generally in the range 79-97%. One PS catalyst was recycled 14 times without loss of stereochemical performance.

New Simple Polymeric Supports with Hydrazone Linkers for Solid-Phase Synthesis of Ketones and Primary Amines

The preparation of new solid supports with hydrazine anchoring groups and their application to solid-phase synthesis of ketones and primary amines are described. The supports were used for immobilization of ketones, 4-tert-butylcyclohexanone, pentan-3-one, acetone, N-methylpiperidone, N-benzylpiperidone, and tropinone in the form of their hydrazones. The polymer-supported hydrazones were subjected to deprotonation/alkylation procedure (LDA/RX) once or twice. The resulting alkylated products were cleaved off the solid support on treatment with trifluoroacetic acid in tetrahydrofuran providing α-alkylated or α,α′-bisalkylated ketones or were subjected to reductive cleavage with borane in tetrahydrofuran to give β-alkylated or β,β′-bisalkylated primary amines.

Strongly basic macrocyclic triamines, 1,5,9-triazacyclododecanes for solvent extraction of gold(I) cyanide

Solvent extraction of gold(I) dicyanide anion from alkaline gold(I) cyanide solution using unusually basic amine extractants was conducted. 1,5,9-Triazacyclododecane ( 4 ) is known as an unusually basic macrocyclic amine having p K a=12.3–12.7, and is thus a good candidate as a basic amine extractant. Three lipophilic derivatives of 4 expected to stay in the organic phase during gold solvent extraction were synthesized. N-Dodecyl-1,5,9-triazacyclododecane ( 3 ) was prepared from 1,5,9-triazacyclododecane-2,4-dione ( 1 ) by N-alkylation with n-dodecyl iodide and then reduction with BH 3-THF. N, N′-Didodecyl-1,5,9-triazacyclododecane ( 5 ) and N, N′, N′′-tridodecyl-1,5,9-triazacyclododecane ( 6 ) were efficiently synthesized by selective di-alkylation of 4 with n-dodecyl iodide, and by reductive alkylation of 4 with n-dodecanal, respectively. The extractants 3 and 6 showed pH 50=10.5, which is the minimum value required for practical application.

Synthesis of Benzene- and Pyridinediboronic Acids via Organotin Compounds

1,4- and 1,3-Bis(trimethylstannyl)benzenes as well as 2,5- and 2,6-bis(trimethylstannyl)pyridines react with borane in THF to give intermediates which on hydrolysis lead to benzene- and pyridinedib...

Role of NaBH(4) stabilizer in the oxazaborolidine-catalyzed asymmetric reduction of ketones with BH(3-)THF.

When stabilized BH(3-)THF (BTHF) was added to a mixture of ketone and tetrahydro-1-methyl-3,3-diphenyl-1H,3H-pyrrolo[1,2-c][1,3,2]oxazaborole (MeCBS-ozaxaborolidine, MeCBS) catalyst 1, low enantioselectivities resulted. Several relative rate experiments showed that a borohydride species in BTHF catalyzed the nonselective borane reduction of ketones, effectively competing with enantioselective MeCBS reduction of ketones, lowering the overall selectivity of the reaction. Improved enantioselectivities in the reaction are obtained by reversing the mode of addition (ketone to BTHF and catalyst), lowering the concentration of NaBH(4) stabilizer in the BTHF solution (87-95% ee) and increasing the concentration or addition rate of BTHF. Decreased reaction temperature and increased catalyst loading only slightly improved the selectivity of the reaction. Upon reaction parameter optimization, simultaneous addition of substrate and BTHF to MeCBS catalyst stabilizer resulted in the highest overall enantioselectivities (96% ee) and diminished the effect of the borohydride. Alternatively, the addition of Lewis acids such as BF(3-)THF to the reaction mixture effectively destroyed the NaBH(4) stabilizer in BTHF solutions, restoring the enantioselectivity to acceptable levels.

Asymmetric reduction of aromatic ketones catalyzed by using (αs, 4s)-2-dichloromethyl-4, 5-dihydro-α-(4-nitrophenyl)-4-oxazolemethanol-borane complex

Chiral oxazoborolidine borane complex was prepared from (αs, 4s)-2-dichloromethyl-4, 5-dihydro-α-(4-nitrophenyl)-4-oxazolemethanol with Borane in THF. The borane modified by chiral oxazoborolidine enantioselectively reduced aromatic ketones to second-alcohol with about 95% yield and medium optical yields. In the end of article, results are discussed and reduction mechanism is shown which proves the resulting major isomers fit very well.

A solution of borane in tetrahydrofuran. A stereoselective reducing agent for reduction of cyclic ketones to thermodynamically more stable alcohols.

A solution of borane in tetrahydrofuran. A stereoselective reducing agent for reduction of cyclic ketones to thermodynamically more stable alcohols.

Conformationally restricted tricyclic analogues of lipophilic pyrido[2,3‐d]pyrimidine antifolates

AbstractThe effect of conformational restriction of the C9‐N10 bridge on inhibitory potency and selectivity of trimetrexate against dihydrofolate reductase, was studied. Specifically three nonclassical tricyclic 1,3‐diamino‐8‐(3′,4′,5′‐trimethoxybenzyl)‐7,9‐dihydro‐pyrrolo[3,4‐c]pyrido[2,3‐d]pyrimidin‐6(5H,8H)‐one (4), 1,3‐diamino‐8‐(3′,4′,5′‐trimethoxybenzyl)‐9‐hydro‐pyrrolo[3,4‐c]pyrido[2,3‐d]pyrimidin‐6‐(8H)‐one (5) and 1,3‐diamino‐(8H)‐(3′,4′,5′‐trimethoxybenzyl)‐7,9‐dihydro‐pyrrolo[3,4‐c]pyrido[2,3‐d]pyrimidine (7) antifolates were synthesized. The tricyclic analogues 4 and 5 were obtained via the regiospecific cyclo‐condensation of the β‐keto ester 17 with 2,4,6‐triaminopyrimidine. The analogue 7 was obtained via reduction of the lactam 4 with borane in tetrahydrofuran. Compounds 4, 5 and 7 were evaluated as inhibitors of dihydrofolate reductase from Pneumocystis carinii, Toxoplasma gondii and rat liver. All three compounds were more selective than trimetrexate against Pneumocystis carinii dihydrofolate reductase and significantly more selective than trimetrexate against Toxoplasma gondii dihydrofolate reductase compared with rat liver dihydrofolate reductase.

Transmetallations between aryltrialkyltins and borane: synthesis of arylboronic acids and organotin hydrides

Aryltrialkyltin compounds react with borane in THF to give mixtures of trialkyltin hydrides and arylboranes, which on hydrolysis give arylboronic acid in high yields. The arylboronic acids are easily separated and obtained free of organotins.

Synthesis and structure of [(η 5-C 5Me 5)WCl 2(μ-H)] 2. A dinuclear tungsten hydride with a double bond formed from the reaction of BH 3THF with (η 5-C 5Me 5)WCl 4

The reaction of limited quantities of BH 3THF with Cp*WCl 4, Cp*=η 5-C 5Me 5, leads to the formation of [Cp*WCl 2(μ-H)] 2 and BH 2Cl in good yield. Structural characterization by spectroscopic and crystallographic techniques reveals the presence of two Cp*WCl 2 fragments in a transoid arrangement connected by a formal WW double bond ( d WW=2.5150(5) Å) bridged by two hydrogen atoms. Reaction of [Cp*WCl 2(μ-H)] 2 with additional BH 3THF leads ultimately to Cp* 2W 2B 5H 9, thereby providing information on the role of [Cp*WCl 2(μ-H)] 2 as an intermediate in the formation of Cp* 2W 2B 5H 9 from the reaction of Cp*WCl 4 with an excess of BH 3THF.

Steric and electronic effects on the reduction of O-silylated aromatic ketoximes with borane

4-Methoxy acetophenone oximes substituted at the oxygen with TMS, TBS, TIPS and MDPS groups were reduced with borane–THF obtaining the 4-methoxy- N-ethyl aniline as the principal product, up to a 95% yield in the case of the more hindered TIPS group. The 2-methoxy- and 2,4-methoxyacetophenone O-TBS oximes produced only the rearranged secondary aniline. Reduction of 1-indanone O-TBS oximes afforded only the tetrahydroquinoline, whereas the 2-indanone analog provided only 2-aminoindan.

Asymmetric reduction of acetophenone over heterogeneous oxazaborolidine catalysts

The reduction of acetophenone over the heterogeneous catalyst NiB 2–0.1(oxazaborolidine) 0.1 by borane in THF at 273 K is quicker than in homogeneous phase. The catalyst presented high enantioselectivity (ee ≥90%) at low molar ratio provided the ketone was added very slowly to the catalyst and borane complex.

Stereoselective Synthesis of 8-Trialkylstannylmenthols

Trialkyltin menthones of type 2 are obtained selectively by 1,4-addition of trialkylstannyl lithium to (-)-pulegone. Reduction of 2 with borane in THF using as catalyst the reagent prepared from borane and (S)-valinol gave a mixture of the corresponding trialkyltin alcohols 3 (Me: 84%; n-Bu: 90,6%) and 4 (Me: 16% and n-Bu: 9,4%).

Studies on the asymmetric reduction of β-oximino methyl ether boronates: reagent control, double diastereocontrol and transmitted remote asymmetric induction

High asymmetric induction (94% ee) could be obtained in the reduction of the achiral E-oxime ether boronate 5 with a homochiral oxazaborolidine 13–BH3–THF complex. Application of this homochiral reducing agent system to non-aromatic oxime ethers 21 produced low to moderate asymmetric induction. Application of the same homochiral reducing agent system to reduction of homochiral boronate E-oximes 3 and 4 produced extreme double diastereoselection effects, i.e. 8 and 95% ee respectively, which demonstrated that remote asymmetry was being ‘transmitted’ by a suitable choice of a ‘partner’ molecule from the boronate moiety to the oxime during reduction. However, attempts to obtain direct remote asymmetric induction in the reduction of homochiral β-oximino boronate methyl ethers 3 and 4 to the corresponding amines produced zero, with for example BH3–THF complex, up to 28% ee with an Et3N–BH3–THF mixture (after oxidative boronate ester cleavage).

Asymmetric reduction and hydrogenation over heterogenous catalysts prepared by reacting nickel-boride with norephedrine

The reduction of acetophenone with borane–THF over heterogeneous catalysts prepared by reacting nickel-boride with (1 R,2 S)-(−)-norephedrine, afforded ( R)-(+)-1-phenylethanol with high enantioselectivity (ee=90%). The catalysts can be recycled two times with little or no loss of performance. The excellent enantioselective properties resulted from the formation of 1,3,2-oxazaborolidine which is strongly anchored at the surface of the nickel-boride. Used for the hydrogenation of acetophenone, 4-methylpentan-2-one and isophorone, the catalyst hydrogenated with a slight predominance of the S configuration. The ee was poor but it remained constant when the catalyst was reused.

Solvates of Sodium Bis(borane)dimethylamide

The reaction of sodium metal with dimethylamine–borane in THF yields Na[(H3B)2NMe2] (1) which can be isolated as {Na[(H3B)2NMe2]}5·THF or as Na[(H3B)2NMe2]·15-crown-5 (2) and Na[(H3B)2NMe2]·benzo-15-crown-5 (3) after addition of the appropriate crown ether to the THF solution of 1. Reaction of 1 with ZrCl4 yields Me2HN–BH2–NMe2–BH3 (4), the structure of which has been determined. In THF solution, 1 reduces aldehydes, ketones, acyl chlorides, and esters to the corresponding alcohols. It also reacts slowly with nitriles and allylbenzene. Compound (1)5·THF crystallizes in an extended three-dimensional lattice, in which the Na atoms are coordinated by 6–9 hydridic H atoms, while 3 is a molecular compound in the solid state. Only one hydrogen atom of each BH3 group coordinates to the sodium center. On the other hand, 4 forms dimeric associates in the solid state through N–H···H–B interactions.

ChemInform Abstract: A Synthesis of 3‐Fluoroindoles and 3,3‐Difluoroindolines by Reduction of 3,3‐Difluoro‐2‐oxindoles Using a Borane Tetrahydrofuran Complex.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.