Vinyl triflates cross-coupling reactions

Most of the work on the C-N bond-forming crosscoupling reactions has concentrated on the formation of aromatic C-N bonds. Recent studies show that the application of cross-coupling reactions to alkenyl halides or triflates furnished enamines (Scheme 19) (for palladium-catalyzed reaction, see 28,28a-28d, and for copper-catalyzed reaction, see 28e-28g). Brookhart et al. studied the palladium-catalyzed amination of 2-triflatotropone 109 for the synthesis of 2-anilinotropone 110.28 It was found that the reaction of 109 proceeded effectively in the presence of racemic BINAP and a base. As a simple method for the synthesis of enamines, the palladium-catalyzed reactions of alkenyl bromide 111 with secondary amine were achieved under similar conditions.2841 The water-sensitive enamine 112 was isolated as pure compound after dilution with hexane and filtration through Celite. The intramolecular cyclization of /3-lactam 113, having a vinyl bromide moiety, was investigated by Mori s... 

An application of Stille couplings to the solid phase using a traceless A-glycerol linker with 2-stannylindoles has been developed [177]. Only a few examples of the use of 3-stannylindoles in Stille reactions have been described. Ortar and co-workers prepared 169 and 170 and effected Pd-catalyzed cross coupling reactions with several aryl, heteroaryl, and vinyl substrates (bromides, iodides, triflates) to give the expected products 171 in high yields [178]. Enol triflates behave exceptionally well under the Ortar conditions, e.g., 172 to 173. 

Recent contributions from Vogel s group have shown that, under CO atmosphere and in the presence of Pd2(dba)3 and Ph3As, 1-stannyl glycals can be carbonylated and coupled to organic halides (Scheme 6a),38 or vinyl triflates (Scheme 6b),39 in carbonylative Stifle cross-coupling processes.40 Also of interest is the palladium catalyzed cross-coupling reaction of... 

As well as alkenylstannanes [106-108], other classes such as a-heteroatom-substituted alkyltributylstannanes [109] and, more importantly, allylic stannanes [110, 111] also undergo these Sn-Cu transmetalations. Otherwise difficult to prepare, allylic copper reagents may, however, be obtained by treatment of allylic stannanes (produced in turn from organolithium, magnesium, or zinc organometallics) with Me2CuLi LiCN. They enter into cross-coupling reactions with alkyl bromides [110] or vinyl triflates (Scheme 2.52) [111]. 

It was also discovered that aryl and vinyl iodides, bromides, and triflates participated efficiently in cross-coupling reactions with organostannanes when catalyzed by palladlum-on-carbon in the presence of Cu(l) as cocatalyst.1... 

Cross-coupling reactions of alkenylsilicates 114 with aryl or vinyl halides or triflates are catalyzed by a palladium complex to give the corresponding alkenes (equation 92)173. 

A different approach to azepine derivatives involved a Pd-catalyzed cross-coupling reaction of the vinyl triflate 49 with the a-alkoxyboronate 50 (R = H) to give 51 in 45% yield acid-catalyzed hydrolysis then gave the azepine derivative 52 and the fused azepine 53, although yields were modest (Scheme 5) <2002JOC7144>. 

Palladium(0)-catalyzed cross-coupling reactions between organic electrophiles (usually vinyl or aryl halides or triflates) and a variety of organometallic reagents and boronic acids have become a popular... 

Regiospecific generation of vinyl triflate 77 from ketones such as 53 and 54 was planned for the introduction of C-4 substituents via palla-dium(0)-catalyzed cross-coupling reactions to give dehydropyrrolidine enamide derivatives 78 which could be reduced stereospecifically to protected kainoid derivatives 79 (Scheme 33). 

A similar Suzuki cross-coupling reaction has also been employed by Gill and Lubell in a synthesis of an unsaturated kainoid analogue.50 Vinyl triflates 97 and 98 were cross-coupled with phenylboronic acid using tetrakis(triphenylphosphine)palladium(0) to give the corresponding coupled products 99 and 100 with high efficiencies (Scheme 42). 

An alternative approach to functionalised azepine derivatives has been reported by Occhiato et al. [02JOC7144] involving a Pd-catalysed cross coupling reaction of the vinyl triflate 33 with the oi-alkoxyboronate 3 4 (R = H) to give 35 in 45% yield acid catalysed hydrolysis then afforded the azepine derivative 37 and the fused azepine 36 in low to fair yields respectively. 

Lithiation of compound 560 with s-BuLi-TMEDA in THF at —78 °C following an inverse addition protocol provided the anion 561. It reacts with primary alkyl iodides and triflates, silyl chlorides, diphenyl disulfide, epoxides, aldehydes, ketones, imines, acyl chlorides, isocyanates and sulfonyl fluorides to yield the expected compounds 562 (Scheme 152). The transmetallation of compound 561 with ZnBr2 allowed the palladium-catalyzed cross-coupling reaction with aryl and vinyl bromides837. When the reaction was quenched with 1,2-dibromotetrafluoroethane, the corresponding bromide 562 (X = Br) is obtained838. 

Unlike other cross-coupling reactions, for which the scope has rapidly expanded in recent years, the range of electrophilic substrates that can be used successfully in the Sonogashira protocol is still rather limited. Vinylic substrates (iodides, bromides, chlorides, triflates, and more recently tosylates) typically yield the best results. For aromatic substrates, iodides and triflates are preferred over bromides, which in turn give far better yields than aryl chlorides. This latter aspect of the reaction is particularly frustrating when one considers the recent advances in the activation of aryl chloride substrates for reactivity in other cross-coupling protocols. ... 

In contrast to the typical palladium(0)-catalyzed cross-coupling reaction of vinyl triflates with organosilanes, this is an example of the reduction of an enone to an alkene by transfer of a proton instead of an alkyl moiety/ ... 

The palladium-catalyzed cross-coupling reaction of a vinyl or aryl stannane with an arylhalogenide or -triflate is known as a Stille reaction. The mechanism of this Stille reaction is outlined below The palladium precatalyst loses two ligands and forms the catalytic species 36. The catalytic cycle starts with the oxidative addition of the catalytic species 36 into the carbon-triflate bond of 23 forming complex 41, which, however, does not undergo the required transmetallation step with stannane 22. Therefore, the triflate ion is... 

Successful extensions to sp-carbon cross-coupling reactions with vinyl triflates are exemplified by the synthesis of the enyne 32 [Eq, (15)]. It is noteworthy that this reaction is compatible with the presence of alkynylsilanes, emphasizing the different behavior of organosilicone and organotin derivatives [25]. 

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