Coupling of Alkynes with Alkenes

Allcylative Cyclization of AUtynyl Enones General Procedure  

Reductive Cydization of AUcynyl Enones General Procediiie l i 

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Reductive coupling of alkynes with alkenes and imines. Alkynes form TaClj complexes, which add to unsaturated alcohols regioselectively. The reaction of such complexes with metalloimines give allylic amines. ... 

Analogically to the coupling of alkynes with alkenes (enones) there is also coupling of allenes with enones to give the dienones 190 (Scheme 82). This process is catalyzed by a number of ruthenium complexes such as 78 or 53 in the presence of a catalytic amount of cerium chloride. The former catalyst is suitable... 

Alkenylsilanes, mainly vinyl silanes and allyl silanes or related compounds, being widely used intermediates for organic synthesis can be efficiently prepared by several reactions catalyzed by transition-metal complexes, such as dehy-drogenative silylation of alkenes, hydrosilylation of alkynes, alkene metathesis, silylative coupling of alkenes with vinylsilanes, and coupling of alkynes with vinylsilanes [1-7]. Ruthenium complexes have been used for chemoselective, regioselective and stereoselective syntheses of unsaturated products. 

Water-soluble palladium(O) complexes have also been used as homogeneous catalysts in aqueous-solution alkylation reactions. The particular complex that has been used is Pd(TPPMS>3. Aryl or heteroaromatic halides can be coupled with aryl or vinyl boronic acids, alkynes, alkenes, or dialkyl phosphites with this palladium(0) complex. This complex in aqueous solution can also be used for the coupling of alkynes with unprotected iodonucleotides, iodonucleosides, and iodoamino acids (133). 

Reductive coupling of alkynes or alkenes may be carried out with Cp2ZrCl2, Ti(0-i-Pr)4, or other Ti(IV) and Zr(IV) complexes. The reaction is often carried out in an intramolecular fashion to achieve better control of regiochemistry. The diyne or other polyunsaturated compound is added to a mixture of the Zr(IV) or Ti(IV) complex and a reducing agent such as BuLi. After formation of the intermediate metallacycle, the C-M bonds are cleaved by treatment with an electrophile such as H+ or I2 to give the organic product. 

Pyridopyrimidines of the [2,3-d], [3,4-d] and [4.,3-d] types may be prepared by reactions involving the cross-coupling of halogenopyrimidines with alkenes and alkynes. For example, 4,-amino-5-iodopyrimidines (298) with S-unsaturated carboxylic esters followed by ring-closure give the pyrido[2,3-d]pyrimidines (299)... 

Besides coupling with alkynes, in 2006 Murakami and co-workers reported [53] a Ni-catalyzed intramolecular coupling of cyclobutanones with alkenes. An asymmetric version of this reaction was reported [54] by the same group in 2012... 

Iron porphyrins containing vinyl ligands have also been prepared by hydromet-allation of alkynes with Fe(TPP)CI and NaBH4 in toluene/methanol. Reactions with hex-2-yne and hex-3-yne are shown in Scheme 4. with the former giving two isomers. Insertion of an alkyne into an Fe(III) hydride intermediate, Fe(TPP)H, formed from Fe(TPP)Cl with NaBH4, has been proposed for these reactions. " In superficially similar chemistry, Fe(TPP)CI (present in 10 mol%) catalyzes the reduction of alkenes and alkynes with 200 mol% NaBH4 in anaerobic benzene/ethanol. For example, styrene is reduced to 2,3-diphenylbutane and ethylbenzene. Addition of a radical trap decreases the yield of the coupled product, 2,3-diphenylbutane. Both Fe(lll) and Fe(II) alkyls, Fe(TPP)CH(Me)Ph and [Fe(TPP)CH(Me)Ph] , were propo.sed as intermediates, but were not observed directly. ... 

In a similar manner, alkynes can undergo sequential carbometallation reactions, previously illustrated in equation (32).136 It is possible to combine carbocupration of alkynes with the use of a Michael acceptor as electrophile when that electrophile is a vinylphosphonium salt, carbocupration can be coupled to Wittig alkenation to result in a stereospecific synthesis of dienes via a one-pot, four-component, four carbon-carbon bond-forming reaction sequence.302... 

The cA-bis(boryl)alkenes 482 are obtained by bis-boration of terminal alkynes catalysed by a Pt complex [185]. Pd and Rh complexes are inactive. Then the (Z)-1,2-diphenylalkene 483 is prepared by Pd-catalysed Suzuki-Miyaura coupling of 482 with iodobenzene. 

In our attempt to extend the coupling reaction of arenes with alkenes to the coupling with alkynes, as shown in Scheme 4, it was found that the reaction of arenes with ethyl propiolate in TFA (trifluoroacetic acid) gave addition products instead of a coupling product [3]. This addition reaction has been extended to various alkynes and various arenes and also to intramolecular reactions for synthesis of heterocycles such as coumarins, quinolines, and thiocoumarins. 

The excellent coordination properties of alkynes with transition metals led to their use as partners for the coupling with a large variety of unsaturated molecules. Two partners such as alkynes and alkenes can produce various modes of C-C bond formation. Linear or cyclic couplings can occur via different pathways, similar to those reported for two C=C bonds couplings (Scheme 1). 

Iron(n) salts mediated the coupling of trialkylboranes with KSGN to give RSCN via a radical process.553,554 Stereochemically pure ( )-l-thiocyanato-alkenes or ( )-l-azide-alkenes were obtained from alkynes when hydro-boration with disiamylborane was followed by reaction with potassium thiocyanate or sodium azide in the presence of copper(n) nitrate, copper(n) acetate, and small amount of water in polar aprotic solvent (Equation (116)).555... 

Cyanosilylation of alkynes with Me3SiCN is effectively catalyzed by a PdCl2 complex.263 Its intramolecular version is valuable for the stereo-defined synthesis of tri- and tetrasubstituted alkenes.264 A Pd-catalyzed system effects an efficient three-component coupling of Me3SiCN, highly electron-deficient alkenes, and allyl chlorides (Equation (69))/ 3 The... 

It is of particular interest that phenanthrene derivatives can also be obtained by the reaction of halobenzenes with alkenes or alkynes. Bromobenzenes react with norbornene to give 2 1 coupling products (Eq. 47) [100]. 

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