Highly Stable Keto-Enamine Salicylideneanilines

Chong, Jonathan H.; Sauer, Marc; Patrick, Brian O.; MacLachlan, Mark J.

doi:10.1021/ol0352714

Cited by 290 publications

(219 citation statements)

References 36 publications

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“…The generation of a keto-enamine species has been previously observed in similar cases and confirmed through X-ray diffraction, being attributed to the relatively higher basicity of the nitrogen against that of the phenolic oxygen. 21 The comparison of the traditionally admitted and the newly proposed TSs, revealed that in the accepted approximation the C-C bond being formed has smaller distances (1.81-1.87 Å) and smaller Wiberg bond indexes (WBI, 0.56-0.59) than in this newly discovered attack mode (Fig. 1).…”

Section: Resultsmentioning

confidence: 87%

A theoretical study of the Duff reaction: insights into its selectivity

2016

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The Duff reaction is one of the most employed methods for the ortho-formylation of phenols; however, not much is truly known about its mechanism. Using DFT calculations, we disclose the first theoretical study regarding the selectivity-determining step of the reaction. We have found that this stage is governed by a hydrogen bond, that gives rise to a cyclohexa-2,4-dienone intermediate and establishes the position where the formylation will take place. These findings were evaluated by analysis of the reaction outcome of several non-symmetrically substituted phenols.

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Section: Resultsmentioning

confidence: 87%

A theoretical study of the Duff reaction: insights into its selectivity

2016

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“…2,4,6-Triformylphloroglucinol (H 3 11) [30] and 2,4,6-triacetylphloroglucinol (H 3 12) [133] were prepared according to reported procedures. The assignments of the NMR resonances (Scheme 7) in all products were supported by 2D COSY, HMBC, and HMQC spectroscopy.…”

Section: Methodsmentioning

confidence: 99%

Electronic and Molecular Structures of Heteroradialenes: A Combined Synthetic, Computational, Spectroscopic, and Structural Study Identifying IR Spectroscopy as a Simple but Powerful Experimental Probe

Richthofen

Feldscher

Lippert

et al. 2013

Zeitschrift Für Naturforschung B

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The vicinity of a hydrogen bond donor (O-H) and a hydrogen bond acceptor (C=O or C=N-R) in salicylaldehydes and ortho-Schiff bases results in significant structural variations compared to the monosubstituted derivatives that are reflected in the electronic structure and thus in the spectroscopic properties. This interplay between intramolecular hydrogen bonding and multicenter π-electron delocalization is the origin of the concept of resonance-assisted hydrogen bonding (RAHB). Herein, the complexity is extended from one hydrogen bond donor-acceptor pair in salicylaldehyde and ortho-Schiff bases to three hydrogen bond donor-acceptor pairs in 2,4,6-tricarbonyl-and 2,4,6-triimine-substituted phloroglucinols (1,3,5-trihydroxybenzene), respectively. To evaluate the changes in the molecular and electronic structures, we have performed a comprehensive computational, spectroscopic, and structural study starting from monosubstituted benzene derivatives as references over ortho-disubstituted derivates to the sixfold-substituted derivatives. Whereas in salicylaldehydes, ortho-Schiff bases, and 2,4,6-tricarbonyl-phloroglucinols the phenolic O-protonated tautomers represent the energy minima, the N-protonated tautomers represent the energy minima in 2,4,6-triiminephloroglucinols. The analysis provides a keto-enamine resonance structure with six exocyclic double bonds to be dominant for these species reminiscent of [6]radialenes, which were termed heteroradialenes. These heteroradialenes are non-aromatic alicycles. However, the predominance of this resonance structure does not represent a sudden change going from the 2,4,6-tricarbonyl-to the 2,4,6-triimine-phloroglucinols, but a gradual increase of analogous resonance structure contributions is observed even in salicylaldehyde and ortho-Schiff bases demonstrating some hetero-orthoquinodimethane character. These changes are, besides in the molecular structures, well reflected in the IR spectra, which can therefore be used as a simple tool to probe the electronic structures in these systems. Interruption of the delocalized π system supporting the intramolecular hydrogen bond, i. e. going from 2,4,6-triimine-to 2,4,6-triamine-substituted phloroglucinols, reestablishes an O-protonated aromatic phloroglucinol system.

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“…This high stability arises from the irreversible nature of the imine-to-enamine tautomeric step, which is attributable to the reasonably large basicity of the -NH group and then the phenolic -OH group, leading to a stable β-ketoenamine linkage. 30 …”

Section: Introductionmentioning

confidence: 99%

Intensified synthesis and post-synthetic modification of covalent organic frameworks using a continuous flow of microdroplets technique

et al. 2018

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Covalent organic frameworks (COFs) are two-dimensional/three-dimensional crystalline polymeric materials with diverse molecular backbones and topologies and are strong candidates for numerous applications. However, the ready availability of these materials is a challenge. The key issues are slow production rates, harsher and longer reaction conditions, and a need for post-synthetic modification to obtain desired molecular functionalities. Only a few studies, including those using microfluidic techniques, have focused on refining these factors, but these reports lack synthetic continuity and scalability. Herein, we present a fast, intensified and continuous synthesis and post-synthetic modification of β-ketoenamine-linked COFs by confining organic building units into moving microdroplets in a transparent capillary. This study introduces a one-step, facile approach to serially modify NO 2 -to NH 2 -substituted COFs in a fraction of the time, effort and cost of traditional methods. These results may stimulate the development of novel COFs with unique chemistries and functions for various applications.

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Highly Stable Keto-Enamine Salicylideneanilines

Cited by 290 publications

References 36 publications

A theoretical study of the Duff reaction: insights into its selectivity

A theoretical study of the Duff reaction: insights into its selectivity

Electronic and Molecular Structures of Heteroradialenes: A Combined Synthetic, Computational, Spectroscopic, and Structural Study Identifying IR Spectroscopy as a Simple but Powerful Experimental Probe

Intensified synthesis and post-synthetic modification of covalent organic frameworks using a continuous flow of microdroplets technique

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