Patent Application
20050107633
The present invention relates to (aryl) (amino)borane compounds and to a process for their preparation.
Arylboronic acids and esters are generally prepared by borylation of aromatic organomagnesium or organolithium derivatives. These methods are expensive, require specific conditions and are not general, which renders them rather unattractive. They have also been prepared by reaction of tetraalkoxydiboron compounds with brominated or iodinated aromatic derivatives in the presence of palladium catalysts (T. Ishiyama et al., J. Org. Chem., 1995, 60, 7508). This method does not involve organomagnesium or organolithium compounds but the preparation of the tetraalkoxydiboron compounds requires the use of molten metallic sodium or potassium at high temperature in highly flammable solvents, which renders the method dangerous. Pinacolborane can react with brominated or iodinated aromatic derivatives in the presence of palladium catalysts to give arylboronic esters of pinacol (M. Murata et al., J. Org. Chem., 1997, 62, 6458). However, pinacolborane, prepared from the borane-dimethyl sulfide complex (Me2S·BH3), is a volatile product used in excess and is not very reactive. The boronic esters obtained are very stable and do not make possible ready refunctionalization around the boron atom.
The aim of the present invention is to provide boranes which can be used in particular in a coupling reaction, that is to say a reaction for the borylation of various derivatives, which can be prepared by a simple process, which exhibit sufficient stability to be stored and which can be readily refunctionalized. For this reason, the subject matter of the present invention is aminoborane compounds and a process for preparing them.
The compounds of the present invention correspond to the formula A-BH-NR1R2, in which:
R1 and R2 are identical or different groups chosen from linear alkyl groups, branched alkyl groups, cyclic alkyl groups or arylalkyl groups, or else the R1 and R2 groups together form an alkylene group, and
A represents:
a) an optionally polycondensed aromatic group optionally carrying at least one substituent,
b) an optionally polycondensed heteroaromatic group optionally carrying at least one substituent,
c) a group chosen from vinyl, dienyl, polyenyl or alkynyl groups optionally carrying at least one substituent,
said optional substituents of the groups defined in a), b) and c) being chosen from alkyls, alkoxys, aminos, dialkylaminos, halogens, nitrile groups, ester groups, amide groups, aldehyde groups protected in the acetal or thioacetal form, ketone groups protected in the acetal or thioacetal form, trialkylsilyl groups and dialkoxyboryl groups.
When an R1 or R2 substituent is an alkyl group, it is preferably chosen from linear alkyls having from 2 to 20 carbon atoms, branched alkyls having from 3 to 20 carbon atoms or cycloalkyls having from 3 to 20 carbon atoms. Mention may be made, by way of example, of isopropyl, cyclohexyl or α-methylbenzyl. The R1 and R2 substituents can be chiral groups.
When an R1 or R2 substituent is chosen from arylalkyl groups, it can be an R8 -Ph-CH(R3) group in which Ph represents a phenyl group, R8 represents H or a substituent chosen from halogens, alkyls, alkoxys, alkylthios, ketone groups protected in the acetal or thioacetal form, and trialkylsilyl groups, and R3 is an alkyl group having from 1 to 20 carbon atoms. Methylbenzyl is particularly preferred.
When R1 and R2 form an alkylene group, the alkylene group is preferably a -CR4R5—(CH2)n-CR6R7— group in which 3≦n≦5 and the R4 to R7 substituents are chosen, independently of one another, from H and alkyl radicals having from 1 to 20 carbon atoms. 1,1,5,5-Tetramethylpentylene is a particularly preferred biradical.
Mention may in particular be made, as examples of substituent A, of phenyl, tolyl and methoxyphenyl.
The compounds of the present invention can be prepared by a two-stage process, in which:
During the first stage, an amine-borane complex R1R2NH·BH3 is prepared and is then converted to aminoborane R1R2NBH2 by heating.
During the second stage, the aminoborane R1R2NBH2 is reacted with a compound A-X, in which X is a leaving group, in the presence of a catalytic amount of a complex of a transition metal and of a base, in an aprotic organic solvent or an amine, and then the excess reactants and solvent are removed. The solvent preferably has a boiling point between 50° C. and 250° C. The leaving group X can be, for example, a halogen atom or a triflate, tosylate, mesylate, diazonium or phosphate group.
In a first embodiment, to prepare the amine-borane complex during the first stage, an amine R1R2NH is reacted under an inert atmosphere with a borane source in a polar aprotic solvent at a temperature of less than 50° C. and then the solvent is removed under vacuum. The borane source can be a commercial complex, such as Me2S·BH3 or THF-BH3. The duration of the reaction is at least equal to 2 hours. The polar aprotic solvent used in this stage is preferably chosen from ethers. Mention may in particular be made of THF, dioxane, DME or diglyme, and tert-butyl methyl ether (TBDME).
In a second embodiment, the amine-borane complex can be prepared during the first stage by reaction of the hydrochloride of the amine R1R2NH·HCl with NaBH4 or KBH4 in an appropriate solvent, such as THF or an ether/water mixture, according to a process described by Polivka et al. (Coll. Czech. Chem. Commun., 1969, 34, 3009). The amine-borane complex R1R2NH·BH3 is subsequently isolated by filtration and removal of the solvent under vacuum.
In both cases, the aminoborane R1R2NBH2 is subsequently obtained by heating the amine-borane complex, followed by distillation. Heating is carried out at a temperature which depends on the nature of the R1 and R2 groups. It is 130° C. for R1=R2=isopropyl. The pure aminoborane obtained after distillation can be stored under an inert atmosphere of nitrogen or of argon.
The organic solvent of the second stage is preferably chosen from ethers, amines and aromatic hydrocarbons. Mention may in particular be made of dioxane, THF, toluene and xylene.
The base introduced into the reaction medium during the second stage of the process is chosen from cyclic or linear trialkylamines, cyclic or linear secondary amines, or aromatic amines of the pyridine or quinoline type.
The complex of a transition metal is preferably a palladium compound stabilized by a ligand. The palladium compound can be chosen from PdCl2, palladium diacetylacetonate Pd(acac)2, palladium acetate Pd(OAc)2, palladium cyanide Pd(CN)2 or allylpalladium chloride (CH2═CHCH2PdCl)2. The ligand can be a phosphine, for example chosen from triphenylphosphine PPh3 or sodium triphenylphosphinetrisulfonate TPPTS. In addition, the ligand can be an arsine, such as, for example, triphenylarsine, an aromatic or nonaromatic nitrile, for example chosen from acetonitrile or benzonitrile, an isonitrile, for example chosen from methyl isonitrile or tert-butyl isonitrile, an aromatic or heteroaromatic imine, such as, for example, N-methylbenzylimine, or an imidazo-2-ylidene, such as, for example, N,N′-dibenzylimidazo-2-ylidene.
A compound according to the present invention can be used as reactant for various reactions and in particular for Suzuki-Miyaura couplings.
A few specific reactions are illustrated below by way of examples by a reaction scheme given in each of the cases for an aminoborane compound in which R1=R2=iPr and A is a phenyl group carrying a Z substituent. Of course, similar reactions can be carried out using aminoborane compounds obtained from amines other than diisopropylamine.
The reaction of a compound according to the invention with a diethanolamine makes it possible to obtain an arylboratrane, according to the following reaction scheme:
The reaction of a compound according to the invention with 2,2-dimethylpropane-1,4-diol makes it possible to obtain a 2-aryl-5,5-dimethyl-1,3,2-dioxaborinane, according to the following reaction scheme:
The reaction of a compound according to the invention with excess methanol makes it possible to obtain an aryldimethoxyborane which can subsequently be hydrolyzed to arylboronic acid, according to the following reaction scheme:
The reaction of a compound according to the invention with a compound A-X in the presence of a Pd(0) catalyst and of a base makes it possible to obtain a (B,B-diaryl)amino-borane compound, according to the following reaction scheme:
The reaction of a compound according to the invention with a compound A-Z in the presence of a Pd(0) catalyst, of a base and of water makes it possible to obtain a compound Ar—Ar, according to the following reaction scheme:
The present invention is described below in more detail with the help of examples, to which it is, however, not limited.
Preparation of the diisopropylamine-borane Complex
50 ml (357 mmol) of diisopropylamine, freshly distilled over calcium hydride, and 50 ml of anhydrous THF are introduced with stirring into a 250 ml Schlenk vessel dried beforehand under argon. The reaction mixture is cooled to −78° C. using an ethanol/liquid nitrogen cold bath and 36.5 ml of the commercial 9.77 m BH3·SMe2 complex (357 mmol) are added dropwise. The temperature of the reaction medium is allowed to rise to ambient temperature over 2 h. The THF is subsequently evaporated on a vane pump under a vacuum of 0.01 mmHg and 41 g of the diisopropylamine-borane complex are obtained in the form of a liquid with syrupy consistency. The spectroscopic characteristics of the compound are given below.
Preparation of diisopropylaminoborane:
A 250 ml Schlenk vessel, containing 41 g (356.5 mmol) of the pure diisopropylamine-borane complex and surmounted by a distillation column equipped with a ground-glass thermometer and connected to a round-bottomed receiving flask and to a bubbler, is brought, using a sand bath, to 160° C. (temperature of the sand). Steady evolution of dihydrogen occurs and is maintained during the rise in temperature. The distillation temperature of the diisopropylaminoborane at the column top is 91-93° C. The diisopropylaminoborane distills in the form of a colorless liquid. 36 g (318.5 mmol) of compound are recovered, corresponding to a yield of 89%. Spectroscopic characteristics:
Preparation of (p-tolyl) (diisopropylamino)borane
0.343 g (0.49 mmol) of palladium catalyst (Ph3P)2PdCl2, 2.129 g (9.8 mmol) of p-iodotoluene, 6.8 ml (49 mmol) of triethylamine, 30 ml of dioxane and 3 ml (19.5 mmol) of diisopropylaminoborane were introduced into a 250 ml Schlenk vessel dried beforehand under argon. The Schlenk vessel was subsequently equipped with a reflux condenser connected at the top to a bubbler. The reaction mixture was stirred magnetically and heated at 70° C. for 15 h. The reaction mixture was subsequently allowed to return, under argon, to ambient temperature. The solvent and the excess reactants were evaporated under the vacuum of a vane pump. The residue obtained was taken up in anhydrous ether and then filtered under argon through dry Celite® 545. The filtrate was again evaporated and the residue was distilled in a Kügelrohr distillation apparatus (T=30-35° C.) under a vacuum of 0.01 mmHg. 1.694 g (Yd=85%) of a colorless oil were isolated. The spectroscopic characteristics are as follows:
Various aryl(diisopropylamino)boranes were prepared from diisopropylamine-borane obtained in accordance with the procedure described in Example 1, according to the following process:
One equivalent of palladium catalyst (Ph3P)2PdCl2, 20 equivalents of aryl halide, 100 equivalents of triethylamine, 700 equivalents of dioxane and 40 equivalents of diisopropylaminoborane are introduced into a 250 ml Schlenk vessel dried beforehand under argon. The Schlenk vessel is subsequently equipped with a reflux condenser connected at the top to a bubbler. The reaction mixture is stirred magnetically and is heated at 70° C. for 15 h. The reaction mixture is subsequently allowed to return, under argon, to ambient temperature. The solvent and the excess reactants are evaporated under the vacuum of a vane pump. The residue obtained is taken up in anhydrous ether and is then filtered under argon through dry Celite® 545. The filtrate is again evaporated and the residue is distilled in a Kügelrohr distillation apparatus under the vacuum of a vane pump. The product obtained from various halides and the yield of the product isolated are shown in the following table.
Preparation of the N,N-dicyclohexylamine-borane Complex
The N,N-dicyclohexylamine-borane complex was prepared by a process analagous to that of Example 1 using N,N-dicyclohexylamine instead of diisopropylamine. 9.52 g of the dicyclohexylamine-borane complex were obtained in the form of a white solid (yield: 97%). The spectroscopic characteristics of the compound are given below.
Preparation of N,N-dicyclohexylaminoborane
N,N-Dicyclohexylaminoborane was prepared by a process analogous to that of Example 1 using the N,N-dicyclohexylamine-borane complex instead of the diisopropyl-amine-borane complex. The N,N-dicyclohexylaminoborane distills at the column top at approximately 129° C. under 0.01 mmHg. 3.644 g (18.9 mmol) of compound are recovered in the form of a colorless oil, corresponding to a yield of 79%. Spectroscopic characteristics:
Preparation of (p-methoxyphenyl) (Dicyclohexylamino)borane
1.130 g (0.19 mmol) of palladium catalyst (Ph3P) 2PdCl2, 0.868 g (3.7 mmol) of p-iodotoluene, 2.5 ml (18.5 mmol) of triethylamine, 15 ml of dioxane and 0.708 g (3.7 mmol) of dicyclohexylaminoborane were introduced into a 100 ml Schlenk vessel dried beforehand under argon. The Schlenk vessel was subsequently equipped with a reflux condenser connected via the top to a bubbler. The reaction mixture was stirred magnetically and heated at 70° C. for 15 h. The reaction mixture was subsequently allowed to return, under argon, to ambient temperature. The solvent and the excess reactants were evaporated under the vacuum of a vane pump. The residue obtained was taken up in anhydrous ether and then filtered under argon through dry Celite® 545. The filtrate was again evaporated and the residue was distilled in a Kügelrohr distillation apparatus (T=40° C.) under a vacuum of 0.01 mmHg. 0.884 g (Yd=81%) of a white solid was isolated. The spectroscopic characteristics are as follows:
The 2,2,6,6-tetramethylpiperidine-borane complex was prepared by a process analogous to that of Example 1 using 2,2,6,6-tetramethylpiperidine instead of diisopropylamine. 9.41 g of the 2,2,6,6-tetramethylpiperidine-borane complex were obtained in the form of a white solid (quantitative yield). The spectroscopic characteristics of the compound are given below.
Preparation of 2,2,6,6-tetramethylpiperidino-1-borane
2,2,6,6-Tetramethylpiperidino-1-borane was prepared by a process analogous to that of Example 1 using the 2,2,6,6-tetramethylpiperidino-1-borane complex instead of the diisopropylamine-borane complex. The 2,2,6,6-tetramethyl-piperidino-1-borane distills at the column top at 50° C. under 0.01 mmHg. 1.842 g (12.1 mmol) of a colorless oil were recovered, corresponding to a yield of 81%.
Spectroscopic characteristics:
Preparation of (p-methoxyphenyl)(2,2,6,6-tetramethyl-piperidino)borane
The above borane was prepared by a process analogous to that of Example 3 using (2,2,6,6-tetramethylpiperidino)borane instead of dicyclohexylaminoborane. 1.562 g of a colorless oil were isolated, which oil distills at 90° C. under 0.01 mmHg. The spectroscopic characteristics are as follows:
Preparation of the [(methylbenzyl)(isopropyl)amine]-borane complex
The (methylbenzyl) (isopropyl)amine-borane complex was prepared by a process analogous to that of Example 1 using (methylbenzyl) (isopropyl) amine instead of diisopropylamine. 16.33 g of the (methylbenzyl) (isopropyl)amine-borane complex were obtained in the form of a white solid (quantitative yield). The spectroscopic characteristics of the compound are given below.
Preparation of [(methylbenzyl)(isopropyl)amino]borane
[(Methylbenzyl)(isopropyl)amino]borane was prepared by a process analogous to that of Example 1 using the (methylbenzyl) (isopropyl)amine-borane complex instead of the diisopropylamine-borane complex. The [(methylbenzyl)(iso-propyl)]aminoborane distills at the column top at approximately 74° C. under 0.01 mmHg. 1.99 g (11.4 mmol) of a colorless oil are recovered, corresponding to a yield of 94%. Spectroscopic characteristics:
Preparation of (p-methoxyphenyl) [(methylbenzyl)-(isopropyl)amino]borane
The above borane was prepared by a process analogous to that of Example 3 using [(methylbenzyl) (isopropyl)amino]-borane instead of dicyclohexylaminoborane. 1.546 g (Yd=51%) of a colorless oil were isolated by distillation at 125° C. under a pressure of 0.01 mmHg. The spectroscopic characteristics are as follows:
| Number | Date | Country | Kind |
|---|---|---|---|
| 01/16734 | Dec 2001 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR02/04512 | 12/20/2002 | WO |
