ChemInform Abstract: Radical Hydrostannylation, Pd(0)-Catalyzed Hydrostannylation, Stannylcupration of Propargyl Alcohols and Enynols: Regio- and Stereoselectivities (original) (raw)

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

The Journal of Organic Chemistry, 2003

A study on the addition of trineophyltin hydride (1) to alkynones under free radical (AIBN and Et 3 B) and palladium-catalyzed [(PPh 3 ) 2 PdCl 2 ] 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 R 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 2-5 with 1 led to addition products in good yields (60-88%); with the more hindered ketones 6 and 7-9 the yields obtained were lower. The radical additions initiated by triethylboron to ynones 2-6 follow a similar pattern but with lower yields; no addition products in the hydrostannation of ynones 7-9 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 1 H, 13 C, and 119 Sn NMR data are given.

Domino reaction: Pd(II)-catalyzed cyclization of unsaturated polyols and cross-coupling

Tetrahedron: Asymmetry, 2012

The Pd-catalyzed cyclization and cross-coupling of hydroxylated alkenes in domino reactions are described. The alkenols undergo Pd-catalyzed cyclization and subsequent cross-coupling reactions with aryl bromides to afford (poly)hydroxylated tetrahydrofuran derivatives. The relationship between the stereoselectivity of the transformation and the steric and/or electronic effects of the substrates has also been studied. The diastereoselectivity of the cyclization of c-hydroxyalkenes 1, 4-6 is influenced by the allylic hydroxyl functionality in favor of 2,3-cis stereoselectivity. Substitution at the C-1 carbon in alkenitols 7 and 8 ensured the formation of products with 2,5-trans diastereoselectivity (up to >19:1), independent of additional substituents.

Cyclization Reactions of Allylic O-Stannyl Ketyls

Journal of Organic Chemistry, 1995

This is a summary of an investigation of the tributyltin hydride-induced cyclization reactions of unsaturated ketones with electronically deficient olefins. This reaction was initiated by an 0-stannyl ketyl formed by the addition of a tributyltin radical to a carbonyl, which has both anionic and radical character. The intramolecular coupling produced functionalized cyclopentanes, bearing two synthetically useful carbon appendages. An activating or electron-withdrawing function on the alkene was essential to the cyclization. A dilution study revealed that excellent anti stereoselectivities ('50:l) could be achieved, and this was attributed to a reversible cyclization. Another goal of this study was to separate the radical reactivity from the anionic reactivity of the 0-stannyl ketyl by the participation of labile functional groups and external electrophiles. The presence of minor products and enolate-trapping studies demonstrated that the anionic character of the ketyl could be utilized in the form of a tin enolate. This work represents the first free radical-and reagentbased approach to the study of the intramolecular hydrodimerization of activated alkenes. ( 5 ) (a) Sugawara, T.; Otter, B. A.; Ueda, T.

Promiscuous Substrate Binding Explains the Enzymatic Stereo- and Regiocontrolled Synthesis of Enantiopure Hydroxy Ketones and Diols

Advanced Synthesis & Catalysis, 2009

Regio-and stereoselective reductions of several diketones to afford enantiopure hydroxy ketones or diols were accomplished using isolated alcohol dehydrogenases (ADHs). Results could be rationalised taking into account different (promiscuous) substrate-binding modes in the active site of the enzyme. Furthermore, interesting natural cyclic diketones were also reduced with high regio-and stereoselectivity. Some of the 1,2-and 1,3-diketones used in this study were reduced by employing a low excess of the hydrogen donor (2-propanol) due to the quasi-irreversibility of these ADH-catalysed processes. Thus, using lower quantities of co-substrate, scale-up could be easily achieved.