Non-fluoride-promoted coupling

A survey of coupling partners shows this to be a very general method that tolerates several functionaHties and proceeds readily at room temjjerature. Unlike most TBAF-promoted reactions, however, the Z-isomer of the silanol reacts at a much lower rate than the -isomer. In general, electron-deficient aryl iodides couple faster than their electron-rich counterparts. The synthetic potential of this new method of activation is clearly demonstrated in the synthesis of ( )-and (Z)-64. The coupHng reaction occurs cleanly in the presence of a TBS (t-butyldimethylsilyl)-protected alcohol, without any observable deprotection. Thus, not only is the compatibihty with silyl protective groups estabhshed, the concept of employing the silanol moiety as a prosthetic group for controlled carbon-carbon 

As in the fluoride-promoted couphng reaction of silanols with triflates, water is essential for the success of this reaction. The added water may increase the solubility of the base or disfavor the silanol to disiloxane conversion (the latter being unreactive in this system). The optimal hydration level is determined to be three moles of water per mole of cesium carbonate. [(Allyl)PdCl 2 is the most 

Clearly, the promoter-less coupling discussed previously follows a pathway that is mechanistically distinct from all the other reported palladium-catalyzed silanol cross-couplings, namely, that of a Heck-type process. Another use of organosi-lanols in coupling reactions that proceed by a unique pathway has been reported by Sames et al. [48] In studies with the ortho-t-butylaniline substrate 75 (arising 

This coupling works equally well for both aryl- (76) and alkenylsilanols (78). 

Finally, both PhB(OH)2 and PhSnBuj fail to react under these conditions, thereby highlighting the importance of silicon in this particular system. 

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