Palladium-Catalyzed Silastannation of Secondary Propargylic Alcohols and their Derivatives

Pd-catalyzed element-element addition to alkynes-a route to bis-functionalized alkenes

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Tanner et al. has reported the silastannation reaction of several secondary terminal propargylic alcohols (protected and unprotected) with Pd2(dba)3·CHCl3/ Ph3P (1-2 equivalents of per Pd). Excellent regio and stereoselectivity (cis addition with tin always added to the internal position) in good to excellent yields (61- 95%) are reported. Application of this method to functionalize the terminal acetylenic moiety (as a part of a complex indole system) with a chiral methyl group in place of a secondary alcohol provided the desired silastannane product in good yields (70-76%), with complete regioselectivity and preservance of chirality as confirmed by X-ray analysis. Reaction went to completion in 4 h instead of overnight reflux as the catalyst and ligand loading was doubled.

Based on the success I had with the catalytic system reported in this paper, the system appears to be more general and has the potential to be expanded to other terminal acetylenes with diverse substituents at the α position. 



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