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Please use this identifier to cite or link to this item: http://hdl.handle.net/123456789/12935

Title: Computational study on the mechanism of transition metal-catalyzed formation of highly substituted furo [3,4-d] [1,2] oxazines
Authors: Gyamfi, Abigail Owusuwaa
Yeboah, Martin Amponsah
Tia, Richard
Adei, Evans
Keywords: Furo [3,4-d] [1,2] oxazine
2-(1-alkynyl)2-alken-1-one
nitrone
1,3-dipolar cycloaddition
density functional theory
gold catalysis
Issue Date: 6-Feb-2018
Publisher: World Scientific Publishing Company
Abstract: The mechanism of gold(III)-catalyzed 1,3-dipolar [3 þ 3] cycloaddition reactions of 2-(1-alkynyl)-2-alken-1-ones with nitrones to a®ord highly-substituted furo [3,4-d] [1,2] oxazines, which are useful as structural skeletons in biologically active compounds and as synthetic building blocks in organic synthesis, have been studied computationally. The results show that the reaction proceeds via the formation of a -complex in which the gold moiety coordinates to the triple bond of the 2-(1-alkynyl)-2-alken-1-ones, resulting in an intramolecular cyclization of the gold intermediate to generate a carbocation intermediate which is trapped by the nucleophilic oxygen of the nitrone to form a furanyl–gold complex, which upon subsequent cyclization a®ords the furo [3,4-d] [1,2] oxazine as well as regenerates the gold catalyst. The highest activation barrier in the entire cycle is 19.5 kcal/mol which accompanies the intramolecular cyclization step. The activation barriers for the reactions of 2-(1-alkynyl)2-alken-1-ones with electron-donating and cyclic substituents are generally lower compared to those of the parent 2-(1-alkynyl)2-alken-1-one while the reactions of 2-(1-alkynyl)2-alken-1-ones with electron-withdrawing substituents have higher activation barriers. Preliminary exploratory calculations on the possibility of replacing gold, an expensive and rare metal, with a copper-based catalyst for the reaction, show that for the key elementary steps, the Cu (III) catalyst is at least as active as the Au (III) complex, thus providing a cheaper route to furo [3,4-d] [1,2] oxazine.
Description: An article published by World Scienti¯c Publishing Company and also available at DOI: 10.1142/S0219633618500116
URI: http://hdl.handle.net/123456789/12935
Appears in Collections:College of Science

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