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Andre M Beauchemin - One of the best experts on this subject based on the ideXlab platform.
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intramolecular alkene aminocarbonylation using concerted cycloadditions of amino Isocyanates
Chemistry: A European Journal, 2016Co-Authors: Ryan A Ivanovich, Jeanfrancois Vincentrocan, Jeangregoire Roveda, Christian Clavette, Serge I Gorelsky, Andre M BeaucheminAbstract:The ubiquity of nitrogen heterocycles in biologically active molecules challenges synthetic chemists to develop a variety of tools for their construction. While developing metal-free hydroamination reactions of hydrazine derivatives, it was discovered that carbazates and semicarbazides can also lead to alkene aminocarbonylation products if nitrogen-substituted Isocyanates (N-Isocyanates) are formed in situ as reactive intermediates. At first this reaction required high temperatures (150-200 °C), and issues included competing hydroamination and N-Isocyanate dimerization pathways. Herein, improved conditions for concerted intramolecular alkene aminocarbonylation with N-Isocyanates are reported. The use of βN-benzyl carbazate precursors allows the effective minimization of N-Isocyanate dimerization. Diminished dimerization leads to higher yields of alkene aminocarbonylation products, to reactivity at lower temperatures, and to an improved scope for a reaction sequence involving alkene aminocarbonylation followed by 1,2-migration of the benzyl group. Furthermore, fine-tuning of the blocking (masking) group on the N-Isocyanate precursor, and reaction conditions relying on base catalysis for N-Isocyanate formation from simpler precursors resulted in room temperature reactivity, consequently minimizing the competing hydroamination pathway. Collectively, this work highlights that controlled reactivity of aminoIsocyanates is possible, and provides a broadly applicable alkene aminocarbonylation approach to heterocycles possessing the β-aminocarbonyl motif.
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diversity oriented heterocyclic synthesis using divergent reactivity of n substituted iso thio cyanates
Chemical Communications, 2015Co-Authors: Jeanfrancois Vincentrocan, Joshua S Derasp, Andre M BeaucheminAbstract:Carbon-substituted Isocyanates and isothiocyanates are common building blocks in organic synthesis. In contrast, synthetic uses of N-substituted Isocyanates and isothiocyanates are severely underdeveloped: few have been reported and their reactivity had not been compared. Herein, we compare the reactivity of blocked (masked) N-Isocyanate and N-isothiocyanate precursors in cascade reactions. Divergent reactivity is observed with secondary propargylic and allylic systems, leading to new syntheses of imidazolones, thiazolidines, and a tool to form complex azomethine imines.
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one pot synthesis of aza diketopiperazines enabled by controlled reactivity of n Isocyanate precursors
Organic Letters, 2015Co-Authors: Ryan A Ivanovich, Jeanfrancois Vincentrocan, Eslam B. Elkaeed, Andre M BeaucheminAbstract:A one-pot sequence for the synthesis of aza-diketopiperazines is reported, involving carbazate acylation with chloroacetyl chloride, SN2 with a primary amine, N-Isocyanate formation, and cyclization. Nitrogen-substituted Isocyanates (N-Isocyanates) are a rare class of amphoteric Isocyanate with high, but severely underdeveloped synthetic potential. This approach highlights that βN-acyl carbazates can act as blocked (masked) N-Isocyanates, thus allowing a challenging intermolecular SN2 reaction of a primary amine to proceed while the N-Isocyanate is “protected”, and then cyclization once it is unmasked. Control experiments show that the alternate pathway—N-Isocyanate substitution and then cyclization by an intramolecular SN2 reaction—is not operating.
P. Andrew Evans - One of the best experts on this subject based on the ideXlab platform.
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Metal-free metathesis reaction of C-chiral allylic sulfilimines with aryl Isocyanates: construction of chiral nonracemic allylic Isocyanates.
Journal of the American Chemical Society, 2014Co-Authors: Rebecca L Grange, P. Andrew EvansAbstract:We report the facile and efficient metal-free metathesis reaction of C-chiral allylic sulfilimines with aryl Isocyanates. This process facilitates the room temperature construction of an array of chiral nonracemic allylic Isocyanates, which are versatile intermediates for the construction of unsymmetrical ureas, carbamates, thiocarbamates and amides. Furthermore, the sulfilimine/Isocyanate metathesis reaction with 4,4′-methylene diphenyl diIsocyanate (4,4′-MDI) circumvents harsh reaction conditions and/or hazardous reagents employed with more classical methods for the preparation of this important functional group.
Rujong Jeng - One of the best experts on this subject based on the ideXlab platform.
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poly urethane malonamide dendritic structures featuring blocked deblocked Isocyanate units
Polymer Chemistry, 2011Co-Authors: Yungchung Chen, Tzongyuan Juang, Shenghong A Dai, Yingling Liu, Rongho Lee, Rujong JengAbstract:We have used 4-isocyanato-4′-(3,3-dimethyl-2,4-dioxoazetidino)diphenylmethane and diethylenetriamine as building blocks to synthesize novel poly(urethane/malonamide) dendrons possessing terminal methyl ethyl ketoxime (MEKO) units (blocked Isocyanate groups). Heating the MEKO-containing dendrons regenerated the terminal Isocyanate groups. Subsequently, the regenerated Isocyanate groups would react with any compound with active hydrogens. In one example, the dendrons with the deblocked Isocyanates further reacted with stearyl alcohol (C18-OH) to form the corresponding dendrons presenting C18 moieties. This deblocking strategy allows replacement of reactive exterior groups with desired functionality for the construction of dendritic macromolecules.
Jeanfrancois Vincentrocan - One of the best experts on this subject based on the ideXlab platform.
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intramolecular alkene aminocarbonylation using concerted cycloadditions of amino Isocyanates
Chemistry: A European Journal, 2016Co-Authors: Ryan A Ivanovich, Jeanfrancois Vincentrocan, Jeangregoire Roveda, Christian Clavette, Serge I Gorelsky, Andre M BeaucheminAbstract:The ubiquity of nitrogen heterocycles in biologically active molecules challenges synthetic chemists to develop a variety of tools for their construction. While developing metal-free hydroamination reactions of hydrazine derivatives, it was discovered that carbazates and semicarbazides can also lead to alkene aminocarbonylation products if nitrogen-substituted Isocyanates (N-Isocyanates) are formed in situ as reactive intermediates. At first this reaction required high temperatures (150-200 °C), and issues included competing hydroamination and N-Isocyanate dimerization pathways. Herein, improved conditions for concerted intramolecular alkene aminocarbonylation with N-Isocyanates are reported. The use of βN-benzyl carbazate precursors allows the effective minimization of N-Isocyanate dimerization. Diminished dimerization leads to higher yields of alkene aminocarbonylation products, to reactivity at lower temperatures, and to an improved scope for a reaction sequence involving alkene aminocarbonylation followed by 1,2-migration of the benzyl group. Furthermore, fine-tuning of the blocking (masking) group on the N-Isocyanate precursor, and reaction conditions relying on base catalysis for N-Isocyanate formation from simpler precursors resulted in room temperature reactivity, consequently minimizing the competing hydroamination pathway. Collectively, this work highlights that controlled reactivity of aminoIsocyanates is possible, and provides a broadly applicable alkene aminocarbonylation approach to heterocycles possessing the β-aminocarbonyl motif.
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diversity oriented heterocyclic synthesis using divergent reactivity of n substituted iso thio cyanates
Chemical Communications, 2015Co-Authors: Jeanfrancois Vincentrocan, Joshua S Derasp, Andre M BeaucheminAbstract:Carbon-substituted Isocyanates and isothiocyanates are common building blocks in organic synthesis. In contrast, synthetic uses of N-substituted Isocyanates and isothiocyanates are severely underdeveloped: few have been reported and their reactivity had not been compared. Herein, we compare the reactivity of blocked (masked) N-Isocyanate and N-isothiocyanate precursors in cascade reactions. Divergent reactivity is observed with secondary propargylic and allylic systems, leading to new syntheses of imidazolones, thiazolidines, and a tool to form complex azomethine imines.
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one pot synthesis of aza diketopiperazines enabled by controlled reactivity of n Isocyanate precursors
Organic Letters, 2015Co-Authors: Ryan A Ivanovich, Jeanfrancois Vincentrocan, Eslam B. Elkaeed, Andre M BeaucheminAbstract:A one-pot sequence for the synthesis of aza-diketopiperazines is reported, involving carbazate acylation with chloroacetyl chloride, SN2 with a primary amine, N-Isocyanate formation, and cyclization. Nitrogen-substituted Isocyanates (N-Isocyanates) are a rare class of amphoteric Isocyanate with high, but severely underdeveloped synthetic potential. This approach highlights that βN-acyl carbazates can act as blocked (masked) N-Isocyanates, thus allowing a challenging intermolecular SN2 reaction of a primary amine to proceed while the N-Isocyanate is “protected”, and then cyclization once it is unmasked. Control experiments show that the alternate pathway—N-Isocyanate substitution and then cyclization by an intramolecular SN2 reaction—is not operating.
Changgeun Chae - One of the best experts on this subject based on the ideXlab platform.
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propagation inspired initiation of an aliphatic sodium amidate for the living anionic homo and copolymerization of Isocyanates access to the multiblocky sequence distribution of binary comonomers
Macromolecules, 2018Co-Authors: Changgeun ChaeAbstract:We report the propagation-inspired initiation of sodium N-phenethyl-3-phenylpropanamide (NaPEPPA), an aliphatic sodium amidate, for the living anionic homo- and copolymerization of Isocyanates. This initiator was compared with sodium benzanilide (NaBA), an aromatic sodium amidate, in the living anionic homopolymerization of n-hexyl Isocyanate (HIC). Only NaPEPPA attained the initiation efficiencies close to unity at the early stage of propagation. The homopolymerization with [HIC]0/[NaPEPPA]0 = 38.9/85.1/203 led to poly(n-hexyl Isocyanate)s (PHICs) with predictable MWs and low dispersities (Mn,theo = 5.12/10.7/24.7 kDa; Mn = 5.22/11.1/27.4 kDa; Đ = 1.11/1.10/1.06). NaPEPPA was also used to initiate the living anionic copolymerization of HIC and furfuryl Isocyanate (FIC). As a result, poly(furfuryl Isocyanate-block-n-hexyl Isocyanate) (P(FIC-b-HIC)) was afforded by the blocky monomer sequence distribution. Based on the copolymerization kinetics, a series of polyIsocyanate-based multiblock copolymers, P(FIC...
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Propagation-Inspired Initiation of an Aliphatic Sodium Amidate for the Living Anionic Homo- and Copolymerization of Isocyanates: Access to the Multiblocky Sequence Distribution of Binary Comonomers
2018Co-Authors: Changgeun Chae, In-gyu Bak, Jaesuk LeeAbstract:We report the propagation-inspired initiation of sodium N-phenethyl-3-phenylpropanamide (NaPEPPA), an aliphatic sodium amidate, for the living anionic homo- and copolymerization of Isocyanates. This initiator was compared with sodium benzanilide (NaBA), an aromatic sodium amidate, in the living anionic homopolymerization of n-hexyl Isocyanate (HIC). Only NaPEPPA attained the initiation efficiencies close to unity at the early stage of propagation. The homopolymerization with [HIC]0/[NaPEPPA]0 = 38.9/85.1/203 led to poly(n-hexyl Isocyanate)s (PHICs) with predictable MWs and low dispersities (Mn,theo = 5.12/10.7/24.7 kDa; Mn = 5.22/11.1/27.4 kDa; Đ = 1.11/1.10/1.06). NaPEPPA was also used to initiate the living anionic copolymerization of HIC and furfuryl Isocyanate (FIC). As a result, poly(furfuryl Isocyanate-block-n-hexyl Isocyanate) (P(FIC-b-HIC)) was afforded by the blocky monomer sequence distribution. Based on the copolymerization kinetics, a series of polyIsocyanate-based multiblock copolymers, P(FIC-b-HIC)1/P(FIC-b-HIC)2/P(FIC-b-HIC)3/P(FIC-b-HIC)4 (Mn,theo = 5.47/10.6/15.8/20.8 kDa; Mn = 5.59/11.5/16.3/20.3 kDa; Đ = 1.10/1.03/1.03/1.03), were afforded by the repetitive sequential addition of comonomers
