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Stereoselective Synthesis of Stannyl Enones via Palladium-Catalyzed and Free Radical Hydrostannation of Alkynyl Ketones with Trineophyltin Hydride

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journal contribution
posted on 26.12.2003, 00:00 by Verónica I. Dodero, Liliana C. Koll, M. Belén Faraoni, Terence N. Mitchell, Julio C. Podestá
A study on the addition of trineophyltin hydride (1) to alkynones under free radical (AIBN and Et3B) and palladium-catalyzed [(PPh3)2PdCl2] conditions is reported. The results obtained indicate that the addition of 1 to eight ynones catalyzed by bis(triphenylphosphine)palladium(II) chloride led in all cases to addition products in very high yields (80−96%). These additions take place with excellent regio- and stereochemistry, leading to the α adducts as major products in seven out of the eight cases studied. Also the E adducts, resulting from a syn attack, were the only (seven cases) or the predominant (one case) products. The radical hydrostannations initiated by AIBN of ynones 25 with 1 led to addition products in good yields (60−88%); with the more hindered ketones 6 and 79 the yields obtained were lower. The radical additions initiated by triethylboron to ynones 26 follow a similar pattern but with lower yields; no addition products in the hydrostannation of ynones 79 were detected. The new acyl-substituted vinylstannanes, owing to their greater stability compared with that of their tributyl- and trimethylstannyl analogues, can be purified by column chromatography using neutral alumina (in all cases) or silica gel 60 (in most cases) as adsorbents. Full 1H, 13C, and 119Sn NMR data are given.