Alkynes Heck-type reactions

The palladium(II)-catalyzed reaction of haloarenes with alkenes and alkynes (Heck-type reactions) in aqueous media has become known only in the preceding few years [Eq. (14)]. 

A similar approach was used by the Alcaide group [183] in the synthesis of tricyclic (3-lactams 6/1-391 from 6/1-390 (Scheme 6/1.99). In this domino process the primarily obtained it-allyl-Pd-complex reacts with the N-nucleophile of the urethane moiety to form a C-N-bond and a vinyl halide. The final step is then an intramolecular Heck-type reaction of the vinyl halide with the alkyne moiety and re-... 

A single alkyne relay is involved in the cascade oligocyclizations of 2-bromoalka-l,w-diene-//-ynes such as 90, 92, 94 and others. Three new rings are formed in these sequences of two intramolecular Heck-type reactions and a 67r-electrocyclization leading to various oligocyclic systems such as 91, 93, 95 in a rather elegant way (Scheme 25). - ... 

A new type of triaryl phosphine-functionalized imidazolium salt containing cations such as (6) has been prepared. Palladium complexes of (6) generated in situ have been used successfully in Heck-type reactions of aryl halides with acrylates and of 4-bromotoluene with styrene derivatives.34 The first Heck-type reaction of aryl halides with allenes has been reported. 1,3-Double arylations were observed with 3-substituted-l,2-allenyl sulfones, while 1-monoarylation was favoured with 3,3-disubstituted-l,2-allenyl sulfones.35 It has been shown that the a-arylation of methane-sulfonamides (7) may be achieved using palladium catalysis reaction proceeds through the sulfonamide enolates.36 It is also reported that palladium cross-coupling of alkynes with /V - (3 - i odophe n y I an i I i ncs) may lead to the formation of substituted carbazoles.37... 

With a combination of organic halide, alkene or alkyne, and palladium catalyst, the reaction may take a superficially similar, but different pathway other than a Heck-type reaction. In these, the halogen is retained in the products, as an alkyl or vinyl halide. These results occur when the starting organic halide is allyl, a- to a carbonyl or similar group, or attached to a perhalogenated carbon atom. In much of the early work, mixtures with Hecklike elimination products were obtained, due to elimination caused by the presence of amine bases in the reaction mixture (equation 165)323. 

Following our first report on the palladium-catalyzed reaction of vinyl triflates with olefins (Heck-type reaction), oxidative insertion of palladium(O) into the carbon-oxygen bond of easily available vinyl triflates has proved to be a general method for the generation of o-vinyl palladium intermediates which can react directly with a variety of olefinic systems, carbon monoxide and alcohols or amines,or 1-alkynes, to give conjugated... 

Here, the term Heck-type reaction is taken to include palladium-catalyzed C-C coupling processes where vinyl or aryl derivatives are functionalized with olefins, alkynes, or organometallic reagents [see Eqs. (1) and (2)] [1]. Aryl and vinyl chlorides are most reluctant to undergo Pd-catalysed activation, as expected from the C-X bond dissociation energies [2]. 

Silylation of Alkynes and Alkenes. A Heck-type reaction of TMS-I with alkenes in the presence of Pd° and EtsN affords alkenyltrimethylsilanes (eq 26). 

Although mechanistically different, functionalized alkenylsilanes are prepared stereoselectively by the reaction of 1-alkynes with iodotrimethylsilane (123) and diethylzinc. At hrst oxidative addition of 123 to Pd(0) generates 125. Then insertion of 1-octyne to 125 affords the alkenylpalladium 126. Transmetallation with Et2Zn gives 127 and reductive elimination provides the alkenylsilane 124. The reaction can be regarded as a Heck-type reaction of alkyne with MesSi-I, followed by Negishi coupling [37]. 

A starting material that is suitable for the direct construction of a heterocycle by an intramolecular Heck-type reaction has to fulfil some simple but fundamental requiranents there has to be the halide function or a triflate for the oxidative addition onto the Pd catalyst, a side chain with an unsaturated functionality such as an alkene or an alkyne in an appropriate distance, and of course the heteroatom in this side chain. Figure 1 presents a substrnctnre typical for very many starting materials, which were transformed to heterocycles by intramolecnlar Heck-type reactions (X = halide, Het = heteroatom). This type of substrnctnre with an allylic side chain is easily accessible by derivatization of 2-bromo- and 2-iodo anilines, phenols, and thiophenols and leads to interesting heterocycles such as indoles and benzofurans, which are related to many natural products and other biological active componnds. 

A tandem reaction occurred when alkyne-substituted cyclobutanone oxime 68 was reacted in the presence of alkenes (Scheme 3.39). The alkylpalladium(II) species generated by P-carbon ehmination was added across the carbon-carbon triple bond, and the resulting alkenylpalladium(II) species underwent a Heck-type reaction with alkenes to afford (allyhdenecyclopentyl)acetonitrile 69. 

Oxidations. Cu(OAc)2 has been used as a reoxidant in Pd catalyzed reactions of aryl and alkenyl boronic acids with alkenes and alkynes, and aryltins, and aryl or alkenyl silanols with electron deficient olefins (eq 26). This Mizoroki-Heck type reaction supposedly proceeds through a Pd(II)-boron transmetallation step, followed by addition across the double (triple) bond and final... 

In a formally similar reaction an alkene and an alkyne moiety were coupled in the presence of a palladium catalyst in formic acid. The reaction cascade in this case starts by the hydropalladation of the triple bond, which is followed by a Heck-type carbon-carbon bond formation. Running the... 

Significant developments have been reported in Heck-type alkylations of alkenes or alkynes. Several reports have addressed the lack of reactivity of aryl chlorides in their reactions with alkenes. Two approaches to this problem have met with success. In the first case, aroyl chlorides are used in place of aryl chlorides under the conditions of reaction, oxidative addition followed by decarbonylation occurs. With activated alkenes, good yields of... 

Heck-type vinylations of alkynic halides proceed only under solid-liquid phase-transfer conditions. These mild conditions allow the reaction to be performed with thermily unstable substrates. Thus, methyl ( )-enynoates can be obtained from the reaction of 1-iodoalkynes with methyl 2-propenoate in DMF at room temperature in the presence of potassium carbonate, tetrabutylammonium chloride and a catalytic amount of palladium acetate (Scheme 36)." ... 

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