Ti-Catalyzed Reactions of Hindered Isocyanates with Alcohols

Spino, Claude; Joly, Marc-André; Godbout, Cédrickx; Arbour, Mélissa

doi:10.1021/jo050712d

Cited by 45 publications

(40 citation statements)

References 14 publications

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“…The termination reaction must be carried out at 08C, due to the reaction of methanol with the remaining monomer to give a carbamate product. 10 This alcohololysis reaction is greatly exothermic and is, probably, catalyzed by the titanium complex or HCl. A sudden rise in the temperature results in polymer degradation and formation of the undesired cyclotrimer, trihexyl isocyanurate.…”

Section: Hexyl Isocyanatementioning

confidence: 99%

Synthesis and characterization of chiral poly(alkyl isocyanates) by coordination polymerization using a chiral half‐titanocene complex

Choinopoulos

Koïnis

Pitsikalis

2015

J. Polym. Sci. Part A: Polym. Chem.

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A new chiral half-titanocene complex, [CpTiCl 2 (O-(S)22-Bu)], is synthesized and characterized by 1 H and 13 C NMR spectroscopy. This complex is employed for the coordination polymerization of n-butyl and n-hexyl-isocyanate leading to chiral polymers, as revealed by their CD spectra. Only the left-handed helix is produced, due to the chiral (S)22-butoxy group, which is bound to the polymer chain end. The polymerization of 3-(triethoxysilyl)propyl isocyanate produces less soluble polymers. On the other hand, phenyl isocyanate reacts slowly with the complex leading quantitatively and selectively to triphenyl isocyanurate. 2-Ethylhexyl isocyanate is slowly and selectively cyclotrimerized in the presence of the half-titanocene complex. However, a statistical copolymer of 2-ethylhexyl isocyanate and hexyl isocyanate is produced. The reaction of benzyl isocyanate with the complex leads to a mixture of low molecular weight polymer and cyclotrimer. The polymers are characterized using SEC, NMR, and CD spectroscopy and their thermal properties are investigated by TGA/DSC analysis.

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Section: Hexyl Isocyanatementioning

confidence: 99%

Synthesis and characterization of chiral poly(alkyl isocyanates) by coordination polymerization using a chiral half‐titanocene complex

Choinopoulos

Koïnis

Pitsikalis

2015

J. Polym. Sci. Part A: Polym. Chem.

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“…The transformation of 4 to a carbamate proved problematic because of the steric hindrance of the adjacent α‐carbon as well as the bulkiness of the alcohols used. Copper(I) chloride, titanium(IV) isopropoxide, and titanium(IV) tert ‐butoxide were tested as Lewis acids to assist in the conversion to the Fmoc‐protected amine; however, titanium(IV) tert ‐butoxide was found to give the best yield. From 5 , hydrolysis of the methyl ester yielded 6 , which was used in synthesis of the target peptides.…”

Section: Resultsmentioning

confidence: 99%

Synthesis of alpha‐methyl selenocysteine and its utilization as a glutathione peroxidase mimic

Wehrle

Ste.Marie

Hondal

et al. 2019

Journal of Peptide Science

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Selenocysteine (Sec) is the 21st amino acid in the genetic code where this amino acid is primarily involved in redox reactions in enzymes because of its high reactivity toward oxygen and related reactive oxygen species. Sec has found wide utility in synthetic peptides, especially as a replacement for cysteine. One limitation of using Sec in synthetic peptides is that it can undergo β‐syn elimination reactions after oxidation, rendering the peptide inactive due to loss of selenium. This limitation can be overcome by substituting Cα‐H with a methyl group. The resulting Sec derivative is α‐methylselenocysteine ((αMe)Sec). Here, we present a new strategy for the synthesis of (αMe)Sec by alkylation of an achiral methyl malonate through the use of a selenium‐containing alkylating agent synthesized in the presence of dichloromethane. The seleno‐malonate was then subjected to an enzymatic hydrolysis utilizing pig liver esterase followed by a Curtius rearrangement producing a protected derivative of (αMe)Sec that could be used in solid‐phase peptide synthesis. We then synthesized two peptides: one containing Sec and the other containing (αMe)Sec, based on the sequence of glutathione peroxidase. This is the first reported incorporation of (αMe)Sec into a peptide as well as the first reported biochemical application of this unique amino acid. The (αMe)Sec‐containing peptide had superior stability as it could not undergo β‐syn elimination and it also avoided cleavage of the peptide backbone, which we surprisingly found to be the case for the Sec‐containing peptide when it was incubated for 96 hours in oxygenated buffer at pH 8.0.

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“…This reaction was originally developed for the titanium(IV) tert-butoxide mediated addition of alcohols to sterically hindered isocyanates to give the corresponding carbamates. [27] In this context it has been shown that tetrakis(dimethylamino)titanium(IV) also mediates the addition of dimethylamine to isocyanates to yield ureas. Treating isocyanates with a tertiary amine such as triethylamine as a catalyst, in 1,4-dioxane at room temperature, gives rise to the formation of the corresponding symmetrical ureas.…”

Section: Acyclic Unfunctionalized Ureasmentioning

confidence: 99%

Acyclic and Cyclic Ureas (Update 2013)

Banert¹,

Dobbs²,

Hall³

et al. 2013

Knowledge Updates 2013/3

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Ti-Catalyzed Reactions of Hindered Isocyanates with Alcohols

Abstract: Highly hindered and sensitive isocyanates react with alcohols under mild catalysis by titanium tetra-t-butoxide to give high yields of the corresponding carbamates.

Cited by 45 publications

References 14 publications

Synthesis and characterization of chiral poly(alkyl isocyanates) by coordination polymerization using a chiral half‐titanocene complex

Synthesis and characterization of chiral poly(alkyl isocyanates) by coordination polymerization using a chiral half‐titanocene complex

Synthesis of alpha‐methyl selenocysteine and its utilization as a glutathione peroxidase mimic

Acyclic and Cyclic Ureas (Update 2013)

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