Linker stannane linkers

Linkers based on sulfur, stannane and selenium chemistry are certainly some of the most flexible systems, because these elements can favorably be tailored for the use as fragile points of attachment. 

Details of the Janda-Chen synthesis were as follows. A tetrahydropyran (THP) linker was attached to the NCPS support enabling attachment of alcohols via THP ether formation.13 The THP-NCPS resin 1 is derivatized with / -(+)-4-hydroxy-2-cyclopentanone 2, giving the THP ether-based resin 3, followed by coupling of the C13 20 fragment by enone-cuprate addition. The cuprate required was generated from the corresponding E-vinyl stannane 4. The resulting enolate was trapped as the silyl end ether... 

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). 

Cleavage reagents Benzyl- type linkers Ketal/ acetal linkers Esters/ amide linkers Silyl linkers Triazene linkers Selenium/ sulfur/ stannane linkers... 

Scheme 6.1.21. A cleavage Stille strategy using a stannane linker for the synthesis of zearalenone 97.

Since the renaissance of solid-phase organic chemistry in 1992, carbon-carbon bond formation reactions on solid support have probably been the best studied reactions. Many different facets of the Suzuki, Heck and Stille reactions have been evaluated. The influence of linkers, catalyst, solvents, microwave, polymer-bound aryl halides or polymer-bound arylboronic acids (or stannanes) have been studied in detail. 

Drawbacks of this method are poor yields and stereoselectivity for substrates having longer spacers between the alcohol and alkyne functionalities (eq 3). As the unsubstituted chain was elongated from one to three methylene units, the yield of Z-vinyl stannane decreased dramatically while the yield of the Z-isomer increased. However, when BuzSnHOTf is employed, consistently high yields are obtained for all linker lengths. 

Scheme 37. Cleavage StiUe strategies using stannane linker. ...

Beyond the Stille reaction, halogen displacement of trialkyltin groups is a widely used reaction in organic synthesis. Thus, halogenation of substrates attached to supports via stannane linker units has also been reported. This reaction is particularly attractive for radiochemists and has been used to prepare radiopharmaceuticals labeled with iodine-123 or iodine-131, such as [ l]MIBG (Table 1.17, Entry 5), and [ I]Congo red (Table 1.17, Entry... 

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