Aryl halides with organotin compounds

SCHEME 20.6 Pd-catalyzed C—N cross-coupling of aryl halides with organotin compound. 

In 1979 the reaction of benzyl and aryl halides was reported with mechanistic discussions [8, 9]. The first palladium-catalyzed carbonylative coupling of organic halides with organotin compounds was reported by Tanaka in the same year (Scheme 4) [10,11]. 

Stille coupling was also developed in tlie early 1980s and is similar to Suzuki coupling in its sequence. It is used to couple aryl or vinyl halides or triflates with organotin compounds via oxidative addition, transmetallation, and reductive elimination. The oxidative addition reaction has tlie same requirements and preferences as discussed earlier for tlie Heck and Suzuki reactions. The reductive elimination results in formation of tlie new carbon-carbon bond. The main difference is that tlie transmetallation reaction uses an organotin compound and occurs readily without the need for an oxygen base. Aryl, alkenyl, and alkyl stannanes are readily available. Usually only one of tlie groups on tin enters into... 

The cross-coupling reaction of alkenyl(fluoro)silanes with aryl halides sometimes produces, in addition to the desired ipso-cowpled products, small amounts of cmc-coupled products [14]. The czne-coupling is often striking in the reaction with organotin compounds. The isomer ratio of products produced by the reaction of l-fluoro(dimethyl)silyl-l-phenylethene with aryl iodides is found to depend on the electronic nature of a substituent on aryl iodides (Eq. 11) an electron-withdrawing group like trifluoromethyl and acetyl favors the formation of the ipso-coupled product. To explain the substituent effect, the mechanism depicted in Scheme 3 is proposed for the transmetalation of alkenylsilanes with palladium(ll) complexes. It is considered that an electron-donating substituent on Ar enhances... 

The palladium-catalyzed coupling of aryl and vinyl halides to organotin compounds, known as Stille coupling, is one of the most important catalytic methods of carbon-carbon bond formation. The reaction is generally conducted in polar organic solvents, such as dimethylformamide, with tertiary phosphine complexes of palladium, although phosphine-free complexes or simple Pd-salts are also frequently used as catalysts [8],... 

Pd-catalyzed coupling of aryl or alkenyl halides and triflates with organotin compounds also takes place smoothly to produce the coupling products, which was discovered by Shlle and Kosugi independently and developed by a number of research groups (Eqs. 5.24 and 25) [100-103],... 

Cross-coupling reactions of aryl (vinyl) halides or triflates with organotin compounds (the Stille reaction) can now be regarded as one of the classical methods of organic synthesis [49]. Again, the basic technique requires palladium complexes with phosphine ligands, and the reactions are carried out in anhydrous organic solvents like DMSO, HMPA, etc., often at elevated temperatures. 

By reaction with the appropropriate aryl halides can be prepared a variety of aryltin compounds that are not accessible from the reactions involving arylmagnesium halides and organotin halides (88,89) there is evidence that an aryne intermediate may be involved (90). However, for some purposes, such as the addition to carbonyl compounds, ox-iranes, and oxetanes, to give hydroxyalkyltin compounds, the Sn-Mg reagents may have advantages (see Section II,E) (91-93). 

Organotin compounds R SnCl4- (R = alkyl, n = 1-4) were prepared by reaction of tin powder with alkyl halides in the presence of RaN[(CH2CH20)mCH2CH20R ]3-a (R = alkyl, aryl, arylalkyl, R = H, alkyl, aryl, a =0, 1, 2, m = 0-20). Iodine should... 

As organotin compounds (organostannanes) undergo smooth Pd-catalysed transmetallation, aryl halides react with a wide variety of aryl-, alkenyl- and alkylstannanes [139]. Coupling with allylstannane is the first example [140]. The reaction is called the Migita-Kosugi-Stille or Stille coupling. Aryl, alkenyl, allyl, alkynyl and benzyl... 

---