Organic compounds -- part of the class 532-570 series – Organic compounds – Sulfonate esters
Reexamination Certificate
2000-02-22
2002-03-26
Ramsuer, Robert W. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Sulfonate esters
C560S102000, C560S104000, C585S470000, C585S471000
Reexamination Certificate
active
06362357
ABSTRACT:
TECHNICAL FIELD
This invention relates to Stille coupling reactions, which can be used for chemical synthesis in the polymer and the fine chemical industry.
BACKGROUND
Metal catalyzed coupling reactions of aryl bromides, aryl iodides, and aryl pseudohalides (e.g., triflates) with various substrates is a general method employed for the formation of C—C bonds. Prior art methods generally cannot employ aryl chlorides as formation of C—C bonds. Prior art methods generally cannot employ aryl chlorides as feedstock for these chemical transformations, and require the use of more expensive aryl bromides and aryl iodides. The use of aryl chlorides as chemical feedstock in coupling chemistry has proven difficult but would economically benefit a number of industrial processes. The few prior art methods that can employ aryl chlorides use expensive, air-sensitive phosphine ligands. In addition, phosphine ligands are often difficult to remove from the process product.
Nucleophilic N-heterocyclic carbenes, the imidazoline-2-ylidenes (sometimes commonly called imidazol-2-ylidenes) or so-called “phosphine mimics”, have attracted considerable attention as possible alternatives for the widely used phosphine ligands in homogeneous catalysis. A primary advantage of these ligands is that an excess of the ligand is not required. It appears that these ligands do not dissociate from the metal center, thus preventing aggregation of the catalyst to yield the bulk metal.
THE INVENTION
This invention provides a process for conducting Stille coupling reactions. The catalyst system used in the present invention permits the use of aryl chlorides as substrates in Stille coupling reactions while eliminating the need for phosphine ligands. Furthermore, both electron-donating and electron-withdrawing substituents on the aryl halide or pseudohalide, the organotin compound, or both, in the Stille coupling reaction are tolerated by the catalyst system used in the present invention, and provide the corresponding Stille coupling products in good yields.
An embodiment of this invention provides a process which comprises mixing, in a liquid medium, i) at least one strong base; ii) at least one aryl halide or aryl pseudohalide in which all substituents are other than stannyl groups, wherein the aryl halide has, directly bonded to the aromatic ring(s), at least one halogen atom selected from the group consisting of a chlorine atom, a bromine atom, and an iodine atom; iii) at least one organotin compound wherein the tin atom is quaternary, wherein one group bound to the tin atom is unsaturated at the alpha or beta position, and wherein each of the remaining groups bound to the tin atom is a saturated group; iv) at least one metal compound comprising at least one metal atom selected from nickel, palladium, and platinum, wherein the formal oxidation state of the metal is zero or two; and v) at least one N-heterocyclic carbene. The N-heterocyclic carbene is selected from the group consisting of an imidazoline-2-ylidene wherein the 1 and 3 positions are each, independently, substituted by a secondary or tertiary group which has at least three atoms, or a protonated salt thereof; an imidazolidine-2-ylidene wherein the 1 and 3 positions are each, independently, substituted by a secondary or tertiary group which has at least three atoms, or a protonated salt thereof; a bis(imidazoline-2-ylidene) wherein a bridging moiety is bound to one nitrogen atom of each ring, and wherein the remaining two nitrogen atoms are each, independently, substituted by a secondary or tertiary group which has at least three atoms, or a protonated salt thereof; and a bis(imidazolidine-2-ylidene) wherein a bridging moiety is bound to one nitrogen atom of each ring, and wherein the remaining two nitrogen atoms are each, independently, substituted by a secondary or tertiary group which has at least three atoms, or a protonated salt thereof, or mixtures of two or more of the foregoing.
Further embodiments and features of this invention will be apparent from the ensuing description and appended claims.
The liquid medium for the processes of this invention can include any of a wide range of solvents, and mixtures of solvents are also usable. The exclusion of water is not necessary, but is preferred. Types of solvents that can be used include hydrocarbons, ethers, amides, ketones, and alcohols. Polar solvents are preferred; ethers are a more preferred solvent type. Ethers that may be used include, for example, diethyl ether, di-n-propyl ether, diisopropyl ether, tert-butyl ethyl ether, diheptyl ether, 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran, methyl tetrahydrofuran, glyme (the dimethyl ether of ethylene glycol), diglyme (the dimethyl ether of diethylene glycol), and the like. Cyclic ethers and polyethers are preferred; a highly preferred ether is 1,4-dioxane.
A large variety of strong bases are suitable for use in the processes of this invention. Generally, these are inorganic bases. Alkali metal salts are a preferred group of inorganic bases. Examples of suitable alkali metal salts include, but are not limited to, lithium carbonate, lithium tert-butoxide, sodium acetate, sodium bicarbonate, sodium tert-butoxide, sodium oxide, sodium tetrafluoroborate, potassium acetate, potassium carbonate, potassium tert-butoxide, potassium nitrite, potassium phosphate, potassium sulfite, potassium hexafluorophosphate, cesium acetate, cesium bicarbonate, cesium carbonate, cesium fluoride, cesium nitrate, and cesium sulfate. Alkali metal salts of carboxylic acid anions (e.g., acetate, trifluoroacetate, citrate, formate, oxalate, propionate, tartrate, etc.) are also suitable for use as the inorganic base in this invention. More preferred are salts of potassium and cesium; most preferred are cesium salts. The most highly preferred inorganic base is cesium fluoride. Choice(s) of inorganic base will vary with the particular system of aryl halide or pseudohalide and organotin compound involved. Amine bases are generally not preferred because, to date, they appear to poison the catalyst system of the invention.
Directly bonded to the aromatic ring(s) of the aryl halide or pseudohalide (i.e., aryl halide or aryl pseudohalide) is at least one halogen atom selected from a chlorine atom, a bromine atom, and an iodine atom, or at least one pseudohalide group. The term “pseudohalide group” includes such groups as p-toluenesulfonate (tosylate), and trifluoromethanesulfonate (triflate), methanesulfonate (meslyate), nonaflate (ONf), and aryl diazonium salts (ArN
2
+
X
⊖
, where X
⊖
is halide, BF
4
⊖
, etc.). The aryl halide or pseudohalide can have two or more such halogen atoms with an atomic number greater than nine and/or pseudohalide groups, including combinations of halogen atoms and pseudohalide groups. However, when two or more such groups are present, the halogen atoms with an atomic number greater than nine and/or pseudohalide groups should all be different from each other. For example, when two such substituents are present, they may be a chlorine atom and a bromine atom, or an iodine atom and a tosylate group, or etc. It is preferred that there is only one chlorine atom, bromine atom, iodine atom, or pseudohalide group directly bound to the aryl ring of the aryl halide or pseudohalide. Aryl chlorides are more preferred as the aryl halide reactants. To prevent self-reaction, it is preferred that stannyl groups are not present on the aryl halide or pseudohalide.
The aryl moiety for the aryl halide or pseudohalide can be homocyclic or heterocyclic. Examples of suitable homocyclic aryl moieties include, but are not limited to, benzene, naphthalene, anthracene, phenanthrene, pyrene, biphenyl, acenaphthalene, fluorene, and indene. Heterocyclic aryl moieties that can be used include, for example, furan, thiophene, oxathiolane, thianthrene, isobenzofuran, phenoxathiin, and the like. Nitrogen-containing heterocycles that can be used include, for example, pyridine, indole, and isoxazole, and the like. Benzene is a preferred aryl moiety for the aryl halide or
Huang Jinkun
Nolan Steven P.
Trudell Mark L.
Zhang Chunming
Ramsuer Robert W.
Sackey Ebenezer
Siebarth & Patty, L.L.C.
University of New Orleans Research & Technology Foundation
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