Organotin compounds transmetalation

Organotin compounds such as aryl-, alkenyl-, and alkynylstannanes are useful for the ketone synthesis by transmetallation of acylpalladium 529 and reductive elimination of 530 as shown[389-393]. Acetophenone (531) is obtained by the carbonylation of iodobenzene with Me4Sn. Diaryl ketones... 

However, cycloauration is, sometimes, difficult to achieve with direct activation of a C—H bond and transmetallation reaction of organomercury or organotin compounds with the appropriate gold compounds is, hence, frequently used. This procedure has been used with azobenzene, 36 A, A -dimethylbenzilamine,1937,1938 4,4 -dimethyl-2-phenyl-l, 3-oxaazoline,1938 1 - (dii zene,... 

Tin compounds can be produced by the Nalco-type reactions39 as well as by Cd and Zn mediated methods42,43. The use of organotin compounds in electrodically induced transmetallations has also been described in a study in which Grignard-type allylation of carbonyl compounds has been carried out by electrochemically recycled allyltin reagents44. 

Lithiation by transmetallation of the diastereoisomeric organotin compounds according to equation 70 takes place with retention of configuration. Free rotation of the carboxamide... 

The intermediate fluorinated organolithium compounds display limited stability at low temperature, but can be transmetalated to stable organotin compounds. Pyrolysis then affords highly reactive fluoroacetylenes, e. g. 2.150... 

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... 

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... 

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... 

Organotin compounds and transition-metal reagents react by several major pathways. The reaction can proceed by simple transmetallation ... 

When the ligand system consists of chlorine atoms, monoalkyl- and monoaryl-titanium(IV) compounds are readily made from TiCU by a chlorine atom replacement. The parent compound in this series, MeTiCb, is made conveniently from the reaction of TiCU and dimethylzinc without the use of ethereal solvents, the preparation being carried out in n-pentane or dichloromethane. Other methylating species can be used, such as MeMgBr, MeLi and MeAlCh. When MeLi is used in diethyl ether, an equilibrium takes place between different complexation states of Ti in the resulting MeTiCU with the solvent (equation 8). Transmetallation from organotin compounds like (15 equation 9) has also been utilized to make trichlorotitanium compounds. ... 

The aminostannanes are usually prepared by transmetallation between an organotin compound such as a halide and an aminometallic compound by transamination of a stannylamine by addition of a tin reagent to a multiple bond to nitrogen, or by an ene reaction (equations 16-1-16-4). The Sn-N bond which is formed is very reactive towards moisture and carbon dioxide, and the reactions must be carried out in an inert atmosphere. 

Many of the applications of organotin compounds are specific to one class of compounds (e.g. tin hydrides or allylstannanes) and these topics are covered in the corresponding chapters. On the other hand, reactions involving tin/lithium transmetallation, or palladium-catalysed coupling, can be carried out with a variety of types of organostannanes, and these reactions are collected together in this chapter. These topics have an extensive literature that is beyond the scope of this book, and the treatment here is limited to an outline of the fields, and a guide to the literature. 

Table 22-1 Transmetallation of organotin compounds with butyllithium, followed by trapping with an electrophile.

Organotin compounds are used in many synthetic procedures as stoichiometric reagents (hydrostannolysis, hydrostannation, allylation, Stille coupling, Sn/Li transmetallation, transesterification, etc), and this presents the problem of removing the organotin residues from the required product. This is particularly important in the preparation of pharmaceuticals as these organotin compounds are to some degree toxic. 

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