The Modes of Reaction of Ambident Catioins

Hünig, Siegfried

doi:10.1002/anie.196405481

Cited by 112 publications

(29 citation statements)

References 64 publications

(15 reference statements)

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“…In general, the nucleophilic attack on the cyclic acyloxonium ions (see Fig. 2) can occur in two different pathways, in what is termed as cis ‐pathway 4 O‐nucleophiles such as water, attack the acyl carbon of the cyclic acyloxonium ion to form 1,3‐dioxolan‐2‐ol moiety which can undergo ring opening and lead to the formation of two isomeric hydrolysis products such as 1,2‐ and 1,3‐DAGs. Both of these diesters are capable of forming further acyloxonium ions such as acyloxonium ion II from the 1,2‐diester (see Fig.…”

Section: Introductionmentioning

confidence: 99%

Monitoring cyclic acyloxonium ion formation in palmitin systems using infrared spectroscopy and isotope labelling technique

Rahn

Yaylayan

2011

Euro J Lipid Sci & Tech

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To confirm the possible involvement of acyloxonium ions as reactive intermediates in food related lipids, their formation was monitored in triplamitin, 1,2 dipalmitin, 1-monopalmitin and specifically labelled tripalmitin (1,1,1-13 C 3 ) using Fourier-transform IR spectroscopy (FTIR). Reactions were conducted at 1008C using a mixture of ZnCl 2 and the lipids. When tripalmitin or 1,2-dipalmitin samples were heated at 1008C in the presence of ZnCl 2 a new band centred at 1651 cm À1 was formed and increased over time. When 13 C-labelled tripalmitin (1,1,1-13 C 3 ) was studied the spectrum exhibited an expected 40 cm À1shift from 1651 to 1611cm À1 indicating the involvement of the carbonyl carbon in the formation of the band. The 1-monopalmitin generated a similar but weaker band at higher temperatures and requiring longer times. These observations may indicate that under hydrophobic environment acyloxonium ions are preferentially formed with neighbouring ester groups assisted by the catalytic action of a free hydroxyl group serving as a proton transfer site. In the absence of such a free hydroxyl group tripalmitin undergoes acyloxonium ion formation at a slower rate than 1,2-dipalmitoyl glycerol, whereas, 1-monopalmitoyl glycerol due to the absence of a neighbouring ester shows even slower transformation efficiencies. This order of reactivity may however change in the presence of water.

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Section: Introductionmentioning

confidence: 99%

Monitoring cyclic acyloxonium ion formation in palmitin systems using infrared spectroscopy and isotope labelling technique

Rahn

Yaylayan

2011

Euro J Lipid Sci & Tech

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“…On the basis of the results collected from the control experiments and previous works in the literature, a plausible mechanism for this KOt-Bu-promoted ring-opening N-alkylation is illustrated in Scheme 9. The reaction is proposed to begin with the generation of iminium ether A [27,28], gener- General procedure for the KOt-Bu-catalyzed ring-opening N-alkylation of 2-oxazolines with benzyl chlorides…”

Section: Resultsmentioning

confidence: 99%

KOt-Bu-promoted selective ring-opening N-alkylation of 2-oxazolines to access 2-aminoethyl acetates and N-substituted thiazolidinones

Lin¹,

Zhang²,

Li³

2020

Beilstein J. Org. Chem.

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An efficient and simple KOt-Bu-promoted selective ring-opening N-alkylation of 2-methyl-2-oxazoline or 2-(methylthio)-4,5-dihydrothiazole with benzyl halides under basic conditions is described for the first time. The method provides a convenient and practical pathway for the synthesis of versatile 2-aminoethyl acetates and N-substituted thiazolidinones with good functional group tolerance and selectivity. KOt-Bu not only plays an important role to promote this ring-opening N-alkylation, but also acts as an oxygen donor.

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“…4 ). Iminium ether intermediates, which were not isolated, are ambident electrophiles at positions a (hydrolysis, thioamide formation, or iminium ion reduction) or b (S N 2 azide or thioaryl displacement with clean inversion, or benzylic reduction) 37 – 40 . Figure 4a illustrates how A-ring iminium ethers were telescoped with a sample set of four nucleophiles (13 out of 22 A-ring analogs are shown, arising from 2 A-ring substrates × 4 azides × 4 nucleophiles; full collection given in Supplementary Table 6 ).…”

Section: Resultsmentioning

confidence: 99%

Reagent-controlled regiodivergent ring expansions of steroids

Charaschanya

Aubé

2018

Nat Commun

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Ring expansion provides a powerful way of introducing a heteroatom substituent into a carbocyclic framework. However, such reactions are often limited by the tendency of a given substrate to afford only one of the two rearrangement products or fail to achieve high selectivity at all. These limitations are particularly acute when seeking to carry out late-stage functionalization of natural products as starting points in drug discovery. In this work, we present a stereoelectronically controlled ring expansion sequence towards selective and flexible access to complementary ring systems derived from common steroidal substrates. Chemical diversification of the reaction intermediate affords over 100 isomerically pure analogs with spatial and functional diversity. This regiodivergent rearrangement, and the concept of using chiral reagents to affect regiocontrol in chiral natural products, should be broadly applicable to late-stage natural product diversification programs.

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The Modes of Reaction of Ambident Catioins

Cited by 112 publications

References 64 publications

Monitoring cyclic acyloxonium ion formation in palmitin systems using infrared spectroscopy and isotope labelling technique

Monitoring cyclic acyloxonium ion formation in palmitin systems using infrared spectroscopy and isotope labelling technique

KOt-Bu-promoted selective ring-opening N-alkylation of 2-oxazolines to access 2-aminoethyl acetates and N-substituted thiazolidinones

Reagent-controlled regiodivergent ring expansions of steroids

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