Unequivocal experimental evidence for a unified lithium salt-free Wittig reaction mechanism for all phosphonium ylide types: reactions with β-heteroatom-substituted aldehydes are consistently selective for cis-oxaphosphetane-derived products

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Title: Unequivocal experimental evidence for a unified lithium salt-free Wittig reaction mechanism for all phosphonium ylide types: reactions with β-heteroatom-substituted aldehydes are consistently selective for cis-oxaphosphetane-derived products
Authors: Byrne, Peter A.Gilheany, Declan G.
Permanent link: http://hdl.handle.net/10197/4934
Date: May-2012
Online since: 2013-11-15T17:23:15Z
Abstract: The true course of the lithium salt-free Wittig reaction has long been a contentious issue in organic chemistry. Herein we report an experimental effect that is common to the Wittig reactions of all of the three major phosphonium ylide classes (non-stabilized, semi-stabilized, and stabilized): there is consistently increased selectivity for cis-oxaphosphetane and its derived products (Z-alkene and erythro-B-hydroxyphosphonium salt) in reactions involving aldehydes bearing heteroatom substituents in the B-position. The effect operates with both benzaldehydes and aliphatic aldehydes and is shown not to operate in the absence of the heteroatom substituent on the aldehyde. The discovery of an effect that is common to reactions of all ylide types strongly argues for the operation of a common mechanism in all Li salt-free Wittig reactions. In addition, the results are shown to be most easily explained by the [2+2] cycloaddition mechanism proposed by Vedejs and co-workers as supplemented by Aggarwal, Harvey, and co-workers, thus providing strong confirmatory evidence in support of that mechanism. Notably, a cooperative effect of ortho-substituents in the case of semi-stabilized ylides is confirmed and is accommodated by the cycloaddition mechanism. The effect is also shown to operate in reactions of triphenylphosphine-derived ylides and has previously been observed for reactions under aqueous conditions, thus for the first time providing evidence that kinetic control is in operation in both of these cases.
Funding Details: Irish Research Council for Science, Engineering and Technology
Other funder
Funding Details: University College Dublin for a President’s Research Fellowship
Type of material: Journal Article
Publisher: American Chemical Society
Journal: Journal of the American Chemical Society
Volume: 134
Issue: 22
Start page: 9225
End page: 9239
Copyright (published version): 2012 American Chemical Society
Keywords: Cycloaddition mechanismTriphenylphosphine-derived ylidesKinetic diasteros electivityStereochemical drift
DOI: 10.1021/ja300943z
Language: en
Status of Item: Peer reviewed
This item is made available under a Creative Commons License: https://creativecommons.org/licenses/by-nc-nd/3.0/ie/
Appears in Collections:Chemistry Research Collection

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