The gold(I)-catalysed reaction of N-Boc-protected 6-alkynyl-3,4-dihydro-2H-pyridines, which gives synthetically useful vinylogous amides (-enaminones), has been studied in detail, in order to optimize the reaction conditions, enlarge the scope and gain insight into the mechanism and the structural features that selectively favour the 6-endo-dig oxyauration of the triple bond. Experimental studies and DFT calculations demonstrate that the 6-endo-dig approach is exclusive with substituted alkynes, whereas with terminal alkynes the 5-exo-dig cyclization prevails, despite the large angle (120 degrees) at C-6. The same selectivity was observed with N-Cbz-protected 2-alkynylpiperidines. With these compounds, -amino ketones are obtained as a consequence of the 6-endo-dig attack onto a substituted triple bond. Sedamine alkaloids are easily obtained by this approach.

Gold-Catalysed Synthesis of Exocyclic Vinylogous Amides and β-Amino Ketones: A Detailed Study on the 5-exo/6-endo-dig Selectivity, Methodology and Scope

PRANDI, Cristina;OPPEDISANO, ALBERTO;DEAGOSTINO, Annamaria;
2015-01-01

Abstract

The gold(I)-catalysed reaction of N-Boc-protected 6-alkynyl-3,4-dihydro-2H-pyridines, which gives synthetically useful vinylogous amides (-enaminones), has been studied in detail, in order to optimize the reaction conditions, enlarge the scope and gain insight into the mechanism and the structural features that selectively favour the 6-endo-dig oxyauration of the triple bond. Experimental studies and DFT calculations demonstrate that the 6-endo-dig approach is exclusive with substituted alkynes, whereas with terminal alkynes the 5-exo-dig cyclization prevails, despite the large angle (120 degrees) at C-6. The same selectivity was observed with N-Cbz-protected 2-alkynylpiperidines. With these compounds, -amino ketones are obtained as a consequence of the 6-endo-dig attack onto a substituted triple bond. Sedamine alkaloids are easily obtained by this approach.
2015
2015
15
3251
3265
www.interscience.wiley.com
Amides; Enynes; Gold; Homogeneous catalysis; Nitrogen heterocycles; Regioselectivity; Organic Chemistry; Physical and Theoretical Chemistry
Scarpi, Dina; Begliomini, Stefano; Prandi, Cristina; Oppedisano, Alberto; Deagostino, Annamaria; Gómez-Bengoa, Enrique; Fiser, Béla; Occhiato, Ernesto...espandi
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2318/1530758
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