Guanidines in Organic Synthesis

Ishikawa, Tsutomu

doi:10.1002/9780470740859.ch4

Cited by 63 publications

(66 citation statements)

References 84 publications

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“…1–5 Organic molecules catalyze ring-opening polymerization (ROP) by a variety of mechanisms that are distinct from those of metal alkoxide initiators; the mild conditions and high functional group tolerance of many of these organic catalysts have provided new opportunities for macromolecular synthesis and design. 1,2 Superbases 6 such as N-heterocyclic carbenes (NHCs), guanidines, amidines, isothioureas, and phosphazenes have proven especially effective as organic catalysts for ROP; in the presence of alcohol initiators these catalysts can hydrogen bond to the alcohol or chain-ends to activate them for the ring-opening of strained monomers (Scheme 1, illustrated for lactide). 2 At low initiator (alcohol) concentrations, competitive initiation mechanisms can occur and can be probed by carrying out polymerizations in the absence of alcohols.…”

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confidence: 99%

Cyclopropenimine Superbases: Competitive Initiation Processes in Lactide Polymerization

et al. 2015

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Cyclopropenimine superbases were employed to catalyze the ring-opening polymerization of lactide. Polymerization occurred readily in the presence and absence of alcohol initiators. Polymerizations in the absence of alcohol initiators revealed a competitive initiation mechanism involving deprotonation of lactide by the cyclopropenimine to generate an enolate. NMR and MALDI-TOF analysis of the poly(lactides) generated from cyclopropenimines in the absence of alcohol initiators showed acylated lactide and hydroxyl endgroups. Model studies and comparative experiments with guanidine and phosphazene catalysts revealed the subtle influence of the nature of the superbase on competitive initiation processes.Organocatalysis has proven a versatile strategy for ring-opening polymerization reactions. [1][2][3][4][5] Organic molecules catalyze ring-opening polymerization (ROP) by a variety of mechanisms that are distinct from those of metal alkoxide initiators; the mild conditions and high functional group tolerance of many of these organic catalysts have provided new opportunities for macromolecular synthesis and design. 1,2 Superbases 6 such as Nheterocyclic carbenes (NHCs), guanidines, amidines, isothioureas, and phosphazenes have proven especially effective as organic catalysts for ROP; in the presence of alcohol initiators these catalysts can hydrogen bond to the alcohol or chain-ends to activate them for the ringopening of strained monomers (Scheme 1, illustrated for lactide). 2 At low initiator (alcohol) concentrations, competitive initiation mechanisms can occur and can be probed by carrying out polymerizations in the absence of alcohols. 2,7 In the absence of alcohol initiators, Nheterocyclic carbenes, 8,9 amidines, 10 and isothioureas 11 mediate zwitterionic ring-opening polymerization reactions by a nucleophilic 12 mechanism; this latter strategy has proven useful for generating cyclic macromolecules. 9 Herein, we describe ring-opening polymerization reactions with another class of potent neutral bases derived from bis(dialkylamino)-cyclopropenimines. [13][14][15] Lambert recently showed that these compounds have comparable basicity to phosphazenes, are readily *Corresponding Author: waymouth@stanford.edu. ASSOCIATED CONTENT NMR Spectra, GPC traces, MALDI and ESI-MS of polymers and model studies. This material is available free of charge via the Internet at http://pubs.acs.org HHS Public AccessThree achiral cyclopropenimines bearing N-alkyl substituents (Table 1, right inset) were prepared. [13][14][15] Polymerizations of lactide initiated with 1-pyrenebutanol in the presence of catalytic amounts of cyclopropenimine 1 proceeded rapidly with greater than 85% conversion in 30 seconds (Table S1, Supporting Information). Molecular weights up to 13 kDa were obtained by controlling the monomer to alcohol ratio. The molecular weight distributions ranged from 1.2-1.4 and generally increased over the course of the reaction. These data, coupled with the observations that polymeric ions corresponding to both odd and ...

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confidence: 99%

Cyclopropenimine Superbases: Competitive Initiation Processes in Lactide Polymerization

et al. 2015

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“…In their oxidized state, some GFA compounds are versatile proton‐coupled electron‐transfer (PCET) reagents (2e – ,2H + transfer as shown exemplary for compound 1 in Figure b) , . Reduction of the oxidized (dicationic) form is favored by the distinct Brønsted basicity , , of the reduced state (e.g. protonated tetramethylguanidine exhibits a p K a value of 15.2 in water and 23.3 in CH 3 CN, and protonated tetramethylguanidino‐benzene a p K a value of 12.2 in water and 20.6 in CH 3 CN).…”

Section: Introductionmentioning

confidence: 99%

Redox‐Active Guanidines with One or Two Guanidino Groups and Their Integration in Low‐Dimensional Perovskite Structures

et al. 2019

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Redox‐active guanidines are versatile reagents in redox and proton‐coupled electron‐transfer (PCET) reactions. Recently, they were integrated as sacrificial electron donors for the prohibition of metal oxidation in perovskite materials. Herein we report the synthesis and characterization of several new redox‐active guanidines with aromatic (benzene, naphthalene or anthraquinone) cores. Two of these compounds are then integrated in lead iodide materials. The structure, thermal stability and optical band‐gap of the resulting materials are evaluated.

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“…47 Even though they are more basic than common trialkylamines, the pKa values of their conjugate acids would not warrant them to qualify as superbasic substances. [48][49][50] Nevertheless, their associated anions possess sufficiently high nucleophilicity to attach weakly electrophilic CO2, enabling them to be used in CO2 gas capture and catalysis. 47,[51][52][53][54][55] In this paper, we refer to them as azolate ionic liquids (or salts).…”

Section: Introductionmentioning

confidence: 99%

Sustainable Cyclic Carbonate Production, Utilizing Carbon Dioxide and Azolate Ionic Liquids

Goodrich

Gunaratne

Jacquemin

et al. 2017

ACS Sustainable Chem. Eng.

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Guanidines in Organic Synthesis

Cited by 63 publications

References 84 publications

Cyclopropenimine Superbases: Competitive Initiation Processes in Lactide Polymerization

Cyclopropenimine Superbases: Competitive Initiation Processes in Lactide Polymerization

Redox‐Active Guanidines with One or Two Guanidino Groups and Their Integration in Low‐Dimensional Perovskite Structures

Sustainable Cyclic Carbonate Production, Utilizing Carbon Dioxide and Azolate Ionic Liquids

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