Alkenylstannanes Stille reactions

One of the first cross-coupling reactions performed on solid supports was the Stille reaction [250] which is a paUadium-catalyzed reaction of a trialkylaryl or trialkylalkenyl stannane with an aromatic iodide, bromide or triflate. In contrast to the process in liquid-phase, the organotin reagent is easily removed from the solid-phase because of the subsequent washing processes. Immobilized aryl halides have been frequently coupled with aryl and alkenylstannanes, whereas stan-nanes attached to the solid support have been used less frequently for the StiUe reaction. An example is the synthesis of a benzodiazepine library by EUman et al. Recently, a Stille cross-couphng reaction has been employed in the synthesis of al-kenyldiarylmethanes (ADAM) series of non-nucleoside HlV-1 Reverse Transcriptase Inhibitors (Scheme 3.14) [251]. 

Stannaries have become prominent in multifunctional anchoring groups. A polymer-bound tin hydride 41 has been used to hydrostannylate alkynes under the action of palladium-catalysis to give polymer-bound alkenylstannanes 42. These alkenyl stannanes have been employed in intermolecular [45] and intramolecular Stille reactions [46]. Alkenylstannanes can also undergo protonation to give alkenes 44 in a traceless fashion. This linker is therefore multifunctional (Scheme 6.1.12). 

C.ii.b. Stille Couplings. A polymer-bound tin hydride has been used to hydrostannylate alkynes under palladium catalysis hydrostaimylation to give polymer-bound alkenyl-stannanes.t Alternatively, the latter could be prepared from a polymer-bound tin chloride and an alkenyllithium or -magnesium halide reagent. These alkenylstannanes were employed in intermolecular as well intramolecular Stille reactions. The inter-molecular reactions provided the coupling products in good yields. In addition, the... 

The coupling of benzyl halides with stannanes has been occasionally used in synthesis.One illustrative example is the total syntheses of piericidin A1 (119) and B1 (120).i2o in these syntheses a heterobenzylic Stille cross-coupling reaction of 116 with alkenylstannane 117 proceeded in the presence of a Pd(0) complex bearing bulky PrBuj as the ligand to give key intermediate 118 (Scheme 5.4.23). 

This alternative to the Friedel-Crafts reaction, extensively developed by Stille and coworkers, is particularly important, since the reaction conditions are essentially neutral, and so provides a method for acylation of compounds containing an acid-sensitive functionality which would preclude the use of the Friedel-Crafts reaction. Reaction temperatures are often below 100 C, and high (1000-fold) turnovers of the catalyst have been achieved. Solvents employed include chloroform, toluene, and, on occasions, HMPA. Some reactions have been carried out under an atmosphere of carbon monoxide to prevent excessive decarbonylation of the acyl palladium intermediate. Indeed, carbonylative coupling of alkenylstannanes with allyl halides in the presence of carbon monoxide ca. 3 atm or greater 1 atm =101 kPa) offers an alternative to the Friedel-Crafts acylation, ketones being formed by the reaction of the stannane with the acyl species formed by carbon monoxide insertion into the allyl palladium intermediate. ... 

The Shapiro reaction has also been used to convert sulfonylhydrazones into alkenylstannanes or alkenylboronic acids, which have been employed in Pd-catalyzed Stille or Suzuki coupling reactions.14,15 For example, Keay has described a one-pot... 

B.ii.b. Termination by Boronates (Heck-Suzuki Cascade), Stannanes (Heck—Stille Cascade), or Cyanide Ion. The Heck reaction of aryl or alkenyl halides with norbomene can be terminated by coupling with either a boronate (Scheme 5, Eq. or an alkenylstannane (Scheme 5, Eq. 2) to stereoselectively formed vicinal biscoupling products with formation of two new C,C bonds. 

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