Stannylative coupling

Novel phenanthro[9,1 ()-r/ isoxazoles 37 have been prepared by intramolecular Stille-Kelly stannylation/coupling of o,o -diiodo-4,5-diarylisoxazoles and by PIFA-mediated non-phenolic oxidative coupling of the corresponding non-halogenated substrates <02T3021>. 

Hydrostannyiation of unsaturated bonds and stannylative coupling using organic halides and distannanes are additional reliable methods. These transformations are detailed in Manual-I and Manual-II, as well as many reviews. 

The Boekelheide reaction has been applied to the synthesis of non-natural products with the preparation of quaterpyridines serving as an example. The sequence began with the 2,4-linked bipyridyl-N-oxide 25. Execution under the typical reaction conditions produced the expected bis-pyridone 26. Treatment with POCI3 afforded the corresponding dichloride that was submitted to a palladium-catalyzed coupling with 2-stannyl pyridine to produce the desired quaterpyridine 27. 

Stannyl cuprates couple widi vinyl halides or trlGales [16c-d, 85], and a vinyl stannane produced diis way has been used in die syntliesis of 7-[f )-alkylidetie]-cepbalosporlns [117]. Vinyl substitution reactions slariing Grom ddiydrofciraiis are... 

Stannyl derivatives of 2ff-pyran-2-one, accessible from bromopyranones by cross coupling with organotin reagents, themselves take part in Pd(0)-catalyscd cross coupling with enol triflates. This methodology offers a new approach to steroidal pyran-2-ones <96JOC6693>. 

Arylacetate esters have been generated by coupling aryl bromides with stannyl enolates generated from silyl ketene acetals. 

Oligomer 113 has been prepared in a Stille cross-coupling of 2-iodo-3-hexylthiophene 111 and bis(thrimethyl-stannyl) DTT 112 which was prepared by lithiation of the dibromide 97 followed by stannylation (Scheme 5) <2002CC2424>. 

Cross-coupling to form carbon heteroatom bonds occurs by oxidative addition of an organic halide, generation of an aryl- or vinylpalladium amido, alkoxo, tholato, phosphido, silyl, stannyl, germyl, or boryl complex, and reductive elimination (Scheme 2). The relative rates and thermodynamics of the individual steps and the precise structure of the intermediates depend on the substrate and catalyst. A full discussion of the mechanism for each type of substrate and each catalyst is beyond the scope of this review. However, a series of reviews and primary literature has begun to provide information on the overall catalytic process.18,19,22,23,77,186... 

The synthesis of the second Stille coupling partner 34 was efficiently achieved in three steps. First, 2-bromojuglone (36) [28] was protected as its methoxymethyl ether (46, Scheme 3.7). The quinone was reduced using sodium thiosulfate, and the resulting hydroquinone was protected with methoxymethyl chloride to afford the arene 47. Finally, stannylation using tetrakis-(triphenylphosphine)palladium and hexabutylditin [29] afforded the cross-coupling partner 34 in high yield. 

It is considered that the stannyl or silyl radical and the alkyl radical are reactive intermediates in these reactions. In contrast to the selective formation of the arylchalcogenosilanes in the above radical reactions, the cross-coupling reaction of a hydrosilane with alkyl(aryl)sulfides catalyzed by palladium nanoparticles results in the selective formation of the corresponding alkylthiosilanes.42... 

Vinyl ethers stannylated in the a-position undergo palladium-catalysed coupling with aryl hlides, as shown, for example, in reaction 64312 and 65313a. 

Dipolar cycloaddition reaction of trimethylstannylacetylene with nitrile oxides yielded 3-substituted 5-(trimethylstannyl)isoxazoles 221. Similar reactions of (trimethylstannyl)phenylacetylene, l-(trimethylstannyl)-l-hexyne, and bis (trimethylsilyl)acetylene give the corresponding 3,5-disubstituted 4-(trimethyl-stannyl)isoxazoles 222, almost regioselectively (379). The 1,3-dipolar cycloaddition reaction of bis(tributylstannyl)acetylene with acetonitrile oxide, followed by treatment with aqueous ammonia in ethanol in a sealed tube, gives 3-methyl-4-(tributylstannyl)isoxazole 223. The palladium catalyzed cross coupling reaction of... 

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