Alkenes coupling

The 121/Cl3SiH combination selectively cross-couples alkenes with alkynes intermolecularly to give acyclic homoallylic silanes 127 and 128 (Eq. 22) [73]. 

The moderate level of regioselectivity seen in the alkyne insertion is dependent on added PPI13, but the alkene insertion occurs with excellent regioselectively. This is the only catalytic, late transition metal system shown to intermolecularly couple alkenes with alkynes. 

Coupling of RMgX with dithioacetals.1 In the presence of Cl2Ni[P(C,H,),]2. Grignard reagents react with 1,3-dithiolanes to give cross-coupled alkenes in moderate yield. 

With arylalkenes, only the coupled alkenes were obtained as ( /Z)-mixtures (Equation 103). If a CHjOAc group was present at the other end of the arylalkene, the reaction took a totally different course, leading to an arylation (Equation 104). These results have been interpreted in terms of the generation of an electrophilic radical on homolysis of the C-I bond. 

The assertion by Centi et al. (30) that the reaction proceeds via a series of redox couples was based on experimental results obtained at high butane concentrations and high oxygen conversions. Under these conditions, many V " " sites are formed as the catalyst undergoes a partial reduction. Butane activation requires a couple, whereas the subsequent conversion to MA requires a couple. Alkenes from butane dehydro-... 

Coupling of terminal acetylenes with 3-chloropyridazines has been performed, using the Pd -Cu -EtjNH system, giving 3-(alkynyl)pyridazines in yields of up to 78% phenylacetylene gives (90) with 3-chloropyridazine 1-oxide but only gives tars with the isomeric 2-oxide/ 3-(Alkynyl)cinnolines have been similarly prepared from 3-iodo- and 3-bromo-cinnolines, and attempts to couple alkenes have been reported it is not unusual, in this type of reaction, to obtain small amounts of homo-coupling products i.e. biaryls), but an excellent yield of 3,3 -bicinnolinyl (81%) was obtained from 3-bromo-cinnoline and styrene. 

Catalyst 2 can also be used in a butenolide synthesis on the basis of a ruthenium catalyzed Alder ene type reaction. [6-9] In the course of a reaction sequence directed to the synthesis of acetogenins, Trost et al. coupled alkene 16 with propargyl alcohol 17 in the presence of 2 to give butentolide 18 in up to 82 % yield (Scheme 6). 

Another attractive three-component procedure involves the versatile triazene linker T1 and generates spirooctene 30 from a Mizoroki-Heck reaction of immobilized iodoarene 29 with bicyclopropylidene in the presence of an acrylate derivative (Scheme 14.9) [27, 28], The triazene moiety can be cleaved to diazonium salts which, in turn, act as substrates for Mizoroki-Heck reactions with various alkenes to give spirooctenes 31. The latter can be obtained without the double bond in the coupled alkene if palladium on charcoal is used instead of palladium acetate, hi this case, the same catalyst promotes the Mizoroki-Heck reaction and the subsequent hydrogenation [28]. 

Transition Metal-catalyzed Reactions. Chlorodimethylvinyl-silane has been used in the synthesis of silyl-containing Heck reaction precursors.24 Heck reaction of aryl or alkenyl iodides with dimethylvinylsilylpyridine (36) using Pd2(dba)3 and tri-2-furylphosphine (TFP) produced the coupled alkene products 37 (R = Ph, 2-py, 2-thiophene, and others) in high yields and with exclusive E selectivity due to the pyridine directing group (eq 17). The pyridine moiety was also employed as a phase tag, which enabled easy purification via acid-base extraction. The silicon linker was subsequently cleaved by H2O2 oxidation. ... 

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