Process for preparing a higher cuprate complex

Abstract: A process for preparing a higher order cuprate complex by reacting an alkyne with zirconocene chloride hydride to produce a zirconium intermediate which is reacted with an alkyllithium and a first copper reagent selected from R²Cu(CN)Li or the mixture CuCN and R²Li to produce a higher order cuprate complex.

Description: The invention herein is directed to a process for preparing higher order cuprate complexes of the general formula from alkenyl zirconium compounds as reactive intermediates in organic synthesis. The higher order cuprate complexes are derived from the reaction of a cuprate complex with an alkenyl zirconium compound. The higher order cuprate complexes are useful for preparing omega side chains of prostaglandin analogs and more specifically, 16-hydroxy prostaglandin analog side chains. The state of the art of higher order cuprate complexes is summarized in Synthesis, 4 , p. 325, (1987) where higher order cuprate complexes of the formulae R t RCu(CN)Li 2 , R t Cu(2-thienyl)CNLi 2 , and R t RCu(SCN)Li 2 and their uses are disclosed. R t represents the group transferred to an organic compound to form a carbon to carbon bond in a subsequent reaction with the disclosed higher order cuprate complex. The use of zirconium compounds to prepare prostaglandins is shown in published European catent application 153,689 which describes the preparation of prostaglandin intermediates. The application describes a zirconium compound of the formula wherein X is a halogen and P 1 represents a hydrolyzable protecting group. The zirconium compound is reacted with a compound having the formula wherein CO 2 P 2 represents a hydrolyzable ester group, in an anhydrous, inert organic solvent which contains a salt or a complex of a transition metal as a catalyst. The reaction mixture is treated with a protonating agent to produce a prostaglandin analog compound of the formula The reference describes the use of the zirconium compounds to add an unsaturated omega side chain on a cyclopentenone to form a prostaglandin analog. The reference discloses that the reaction occurs in the presence of a salt or a complex of a transition metal catalyst which includes salts or complexes of nickel, cobalt, iron, manganese and palladium. The reference's preferred complex is a complex or salt of nickel (I) which is produced in situ in the reaction by using a nickel (II) salt (or complex) and a reducing agent. WO-A 9115493 (published after the present priority date but claiming an earlier priority) is related to higher order cuprate complexes by transmetalation from a corresponding zirconate intermediate by reaction with R 2 Cu(A)Li 2 wherein A is CN or SCN. C.A. 114, 61742 to Kalish, Vincent, J., published after the present priority date is related to a method for preparing prostaglandin analogs by hydrozirconation-iodination of a terminal acetylene followed by lithiumiodide exchane and dilithiocyanocuprate- mediated conjugate addition to an appropriate cyclopentenone. JACS, Vol. 112 (1990) pp. 7440-41 to B.H. Lipschutz et al. (a) and pp. 7441-7442 to K.A. Babiak (b) et al., having been published after the present priority, are related to a hydrozirconation-transmetalation reaction by using an alkyne, zirconocene chloride halide and 2 equivalents of butyl/methyllithium, 1 equivalent of CUCN (b) and to the reaction of zirconochloride halide, an alkyne, one equivalent of methyllithium a solution of Me 2 Cu(CN)Li 2 to prepare a higher order vinylic cuprate(a). Summary of the invention The invention herein is directed to a process for preparing a higher order cuprate complex. The process is performed by reacting an alkyne of the formula H ― C ≡ C ― R 1 with zirconocene chloride hydride, Cp 2 Zr(H)Cl, to produce an E-alkenyl zirconium intermediate of the formula wherein R 1 contains 1 to 20 carbon atoms which can have vinyl unsaturation. R 1 can contain cycloalkyl or cycloalkenyl moieties where the cycloalkyl contains 3 to 6 carbon atoms. R 1 can be substituted with hydroxy, tri-lower-alkylsiloxy, tetrahydropyranyloxy, tetrahydrofuranyloxy, halo or phenoxy. The E-alkenyl zirconium intermediate is reacted with an alkyllithium and a copper-containing reagent selected from: R 2 Cu(CN)Li or the mixture CuCN and R 2 Li to produce a higher order cuprate complex intermediate of the formula wherein R 2 can be alkyl, alkenyl, alkynyl, aryl or heteroaromatic such as 2-thienyl. Detailed description The invention herein is directed to a process for preparing a higher order cuprate complex. The process herein is advantageous in that the process can be performed in a single reaction vessel to completion in forming the higher order cuprate complex. The invention herein is directed to a process for preparing a higher order cuprate complex comprising the steps of: (a) bringing into reactive contact, in a single reaction vessel, one equivalent of an alkyne and a sufficient amount of zirconocene chloride hydride to produce an E-alkenyl zirconium intermediate; and (b) adding to the reaction vessel (i); two equivalents of an alkyllithium followed by one equivalent of R 2 Cu(CN)Li; or (ii) two equivalents of an alkyllithium followed by one equivalent of CuCN and one equivalent of R 2 Li; to produce a higher order cuprate complex intermediate, wherein R 2 can be alkyl, substituted alkyl, alkenyl, alkynyl, aryl or heteroaromatic group. The formed higher order cuprate complex can be used in further reaction sequences as is known for cuprate reagents for example to make prostaglandin derivatives The process is performed by reacting an alkyne and a zirconocene chloride hydride, Cp 2 Zr(H)Cl, to produce an E-alkenyl zirconium intermediate. Cp represents a cyclopentadienyl anion group. The E-alkenyl zirconium intermediate need not be isolated but can be reacted with an alkyllithium and a copper-containing reagent which can be: the complex R 2 Cu(CN)Li or the reagent mixture CuCN and R 2 Li to produce a higher order cuprate complex intermediate of the formula wherein R 1 contains 1 to 20 carbon atoms which can have vinyl unsaturation. R 1 can contain cycloalkyl or cycloalkenyl moieties where the cycloalkyl contains 3 to 6 carbon atoms. R 1 can be substituted with hydroxy, tri-lower-alkylsiloxy, tetrahydropyranyloxy, tetrahydrofuranyloxy, halo or phenoxy; and wherein R 2 can be alkyl, alkenyl, alkynyl, aryl or heteroaromatic such as 2-thienyl. The higher order cuprate complex intermediate need not be isolated but can be reacted with an appropriate cyclopentenone to produce a prostaglandin derivative The invention herein is illustrated in the following reaction Schemes I-II. The two reaction schemes illustrate the process herein and the variations in the process. Each of the reaction sequences shown in the reaction schemes can be performed in a single vessel which provides a particularly unique benefit for using the process herein as the performance of the process in a single reaction vessel ("one-pot" reaction) eliminates steps of separating and isolating intermediates and the need for having additional reaction vessels. In the two reaction schemes an alkyne, which can contain additional unsaturation, is reacted with zirconocene chloride hydride to produce a zirconium intermediate which is reacted with an alkyllithium reagent, a copper complex (or reagents to produce the copper complex) and an enone ("enone" is used herein to refer to a cyclopentenone) to produce the prostaglandin derivative. In the reaction Schemes I-II, the processes described are exemplified with 4-methyl, 4-trimethylsilyloxy-1-octyne. It can be understood that other terminal alkynes, such as those described, in examples 2-11, work equally well with the processes depicted in the Schemes I and II. In the structural formulas herein, a wedge shaped bond (▾) represents a substituent which has the β orientation (above the plane of the molecule) and a broken line ( ) represents a substituent that is in the α orientation (below the plane of the molecule) and a wavy line ( ) represents a substituent which is either in the α or β orientation or is a mixture of these isomers. In the above reaction Scheme I a terminal alkyne is reacted with Cp 2 Zr(H)Cl in a suitable solvent such as tetrahydrofuran (THF) to produce a zirconium intermediate of the indicated formula. The zirconium intermediate is reacted sequentially with two equivalents of an alkyllithium such as n-butyllithium (n-BuLi) or methyllithium (CH 3 Li), copper cyanide (CuCN), an alkyllithium such as methyllithium (CH 3 Li) and an appropriate enone which results in the prostaglandin derivative which is represented in this Scheme I as having TMS and TES (trimethylsilyl and triethylsilyl) protective groups for the hydroxyl moieties on the prostaglandin derivative. The reaction is conducted in a single reaction vessel with the reactants being added in the order indicated. The reaction is performed at a reduced temperature preferably in the range of -50°C to -78°C. The reaction sequence shown in Scheme II illustrates another method for preparing prostaglandin derivatives using the invention herein. In reaction Scheme II a terminal alkyne is reacted with zirconocene chloride hydride to yield a zirconium intermediate which is reacted with two equivalents of alkyllithium followed by a lower order cuprate complex, R 2 Cu(CN)Li, and a suitable enone to provide the prostaglandin derivative. The reaction sequence is performed in a temperature range from about -50°C to about -78°C. In the process herein any conventional inert organic solvent or solvent mixture can be used. Aromatic hydrocarbons such as benzene and toluene and ether solvents such as tetrahydrofuran are especially preferred. Temperatures in the range of -50° to -78°C are preferred for performing the reaction with a temperature range from -50° to -60°C being especially preferred. Example 1 This example illustrates a one-pot preparation of a higher order cuprate complex using the method herein and in particular following the reaction sequence shown in reaction Scheme I. A dry, round bottom flask was charged with 776 mg (3.00 mmol) of zirconocene chloride hydride and 4 ml of dry THF under nitrogen. A solution of 604 mg (2.85 mmol) of 4-methyl-4-trimethylsilyloxy-1-octyne in 6 ml of THF was added by cannula. The mixture was stirred at room temperature for approximately 30 minutes and cooled to -50°C. The mixture was treated with 3.56 ml of n-butyllithium (1.6M in hexane, 5.7 mmol) for ten minutes. To the vessel was added 254 mg (2.84 mmol) of copper cyanide and the mixture was stirred for fifteen minutes at -50°C followed by the addition of 2.09 ml of methyllithium (1.39M in cumene/THF, 2.9 mmol). The mixture was stirred for fifteen minutes to generate an orange cuprate solution. Examples 2-11 The procedure of Example 1 was repeated in very essential detail with the exception that the indicated alkynes shown in the following Table 1 were used. Example 12 This example illustrates the method herein employing reaction Scheme II, To an argon filled, flame-dried flask was added 776 mg (7.0 mmol) of zirconocene chloride hydride under nitrogen. The flask was protected from light with foil. To this flask was added 4 ml of THF, followed by a solution of 604 mg (2.85 mmol) of 4-methyl-4-trimethylsilyloxy-1-octyne in 6 ml THF and 2 ml THF rinse. The reaction mixture was stirred at room temperature for approximately 30 minutes to give a light orange solution. To a second flask was added 254 mg (2.85 mmol) of copper cyanide under nitrogen. To the cooled flask was added 5 ml THF and the reaction mixture was cooled to -78°C. To the flask was added via syringe 2.09 ml of methyllithium (1.39M in cumene/THF, 2.9 mmol). The flask was warmed to 0°C for 12-20 minutes and recoded to -78°C. To the light orange colored solution of the zirconium intermediate at -78°C was added n-butyllithium (3.56 ml, 5.7 mmol, 1.6M) dropwise by a syringe. The temperature was maintained at about -70°C during the addition. The mixture was warmed gradually to -30°C over fifteen minutes and held at -30°C for fifteen minutes to give a deeper, orange-colored zirconium solution. The solution was recoded to -78°C and the copper solution was added by cannula while maintaining the temperature at about -78°C. The reaction mixture was warmed briefly to -30°C and recoded to -78°C.

Claims: A process for preparing a higher order cuprate complex comprising the steps of: (a) bringing into reactive contact, in a single reaction vessel, one equivalent of an alkyne and a sufficient amount of zirconocene chloride hydride to produce an E-alkenyl zirconium intermediate; and (b) adding to the reaction vessel (i) two equivalents of an alkyllithium followed by one equivalent of R 2 Cu(CN)Li; or (ii) two equivalents of an alkyllithium followed by one equivalent of CuCN and one equivalent of R 2 Li; to produce a higher order cuprate complex intermediate, wherein R 2 can be alkyl, substituted alkyl, alkenyl, alkynyl, aryl or heteroaromatic group. A process as recited in Claim 1 wherein the reaction is performed in a temperture range from -50°C to -78°C. A process as recited in Claim 1 or 2 wherein the alkyllithium is methyllithium.

Inventors: BABIAK KEVIN ANTHONY, BEHLING JAMES RICHARD, DYGOS JOHN HENRY, SAU-HOI NG JOHN, BABIAK, KEVIN ANTHONY, BEHLING, JAMES RICHARD, DYGOS, JOHN HENRY, SAU-HOI NG, JOHN
Applicants: SEARLE & CO, G.D. SEARLE & CO.
Application year: 1991
Main classification: C07F1
IPC codes: C07F7, C07B61, C07F1, B01J31, C07C405