The Experts below are selected from a list of 53103 Experts worldwide ranked by ideXlab platform
Wenxiong Zhang - One of the best experts on this subject based on the ideXlab platform.
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recent development of synthetic preparation methods for Guanidines via transition metal catalysis
Chemical Communications, 2015Co-Authors: Wenxiong ZhangAbstract:Multisubstituted Guanidines have received much attention because of important applications in many fields, such as pharmaceutics, organometallic and coordination chemistry, and organic synthesis. Although classical methods are available for the preparation of Guanidines, synthetic preparation approaches to Guanidines are still in great demand. In this review, we summarize recent developments on synthetic methods via the C–N bond formation. Three aspects are included: transition-metal-catalyzed guanidine synthesis based on classical methods; catalytic guanylation reaction of amines with carbodiimides; and tandem catalytic guanylation/cyclization reactions.
Murray Goodman - One of the best experts on this subject based on the ideXlab platform.
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Triurethane-Protected Guanidines and Triflyldiurethane-Protected Guanidines: New Reagents for Guanidinylation Reactions
The Journal of Organic Chemistry, 1998Co-Authors: Konrad Feichtinger, Heather L. Sings, Tracy J. Baker, Kenneth S. Matthews, Murray GoodmanAbstract:New guanidinylation reagents are reported. These reagents consist of N,N‘,N‘‘-tri-Boc-guanidine (1) and N,N‘,N‘‘-tri-Cbz-guanidine (2), which allow for the facile conversion of alcohols to substituted Guanidines. A series of arginine analogues were synthesized via condensation of a primary or secondary alcohol with the guanidinylation reagents 1 or 2, under Mitsunobu conditions,1 to produce protected alkylated Guanidines. In addition, an extended study of the previously reported reagents2 N,N‘-di-Boc-N‘‘-triflylguanidine (3) and N,N‘-di-Cbz-N‘‘-triflylguanidine (4) is presented. The triflyldiurethane-protected guanidine 3 was utilized to guanidinylate primary and secondary amines under mild conditions with high yield in both solution and on solid phase.
Tatsuro Yasukata - One of the best experts on this subject based on the ideXlab platform.
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a mild method for the synthesis of carbamate protected Guanidines using the burgess reagent
Organic Letters, 2014Co-Authors: Toshikatsu Maki, Takayuki Tsuritani, Tatsuro YasukataAbstract:A simple method for the synthesis of carbamate-protected Guanidines from primary amines is described. A variety of thioureas derived from primary amines and isothiocyanates react with the Burgess reagent to give the corresponding Guanidines via either a stepwise or one-pot procedure. By tuning the carbamoyl units of isothiocyanates and the Burgess reagent, differentially N,N′-diprotected Guanidines can be obtained. Selective deprotection of the products affords N-monoprotected Guanidines.
Watanabe Teruki - One of the best experts on this subject based on the ideXlab platform.
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Investigation Of The Intramolecular 1,3-Diaza-Claisen Rearrangement In The Ring Expansion Reactions Of Vinyl Pyrrolidines And Vinyl Piperidines
ScholarWorks @ UVM, 2020Co-Authors: Watanabe TerukiAbstract:The 1,3-diaza-Claisen rearrangement was discovered and developed in the Madalengoitia group since 2004. The rearrangement is initiated by the desulfurization of the electron deficient thiourea and isothiourea to obtain the highly electrophilic carbodiimide which can be reacted with an allylic tertiary amine to form the zwitterionic intermediate which then undergoes [3,3]-sigmatropic rearrangement. Previous investigation includes multiple examples of successful formation of complex Guanidines through intermolecular and intramolecular variants. Providing an easy access to guanidine which is one of the most prevalent functional groups in the biologically relevant system, the rearrangement can be a valuable tool in the organic synthesis. The ring expanding 1,3-diaza-Claisen rearrangement is facilitated by the thiophilic metal promoted desulfurization of the isothioureas tethered to vinyl pyrrolidine which affords electron deficient carbodiimide. Addition of the tertiary amine to the carbodiimides via intramolecular cyclization forms zwitterionic spirocycles which then undergo 1,3-diaza-Claisen rearrangements to afford nine-membered ring guanidine containing fused bicycles with cis-alkene. The mechanistic study with the various additives and DFT calculations revealed that Lewis acid promoted cationic [3,3]-sigmatropic rearrangement mechanism is at play which results in dramatic rate acceleration. The substrate scope examination with varying tether lengths and electron withdrawing groups has shown the less electron deficient carbodiimides engage in faster rearrangement and works optimal with shorter carbon tethers. The vinyl piperidine ring expansion reactions exhibited the reaction trend similar to the non-strained system. Desulfurization of both tosyl- and triflate- substituted isothioureas afforded exotic guanidine containing transannular 10-membered ring while le electron withdrawing carbodiimides failed to undergo the rearrangement. Mechanistic investigation with DFT calculations suggested the reaction is zwitterionic [3,3]-rearrangement rather than the cationic [3,3]- rearrangement
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Investigation of the 1,3-diaza-Claisen Rearrangements in Ring Expansion of Vinyl N-heterocycles
ScholarWorks @ UVM, 2019Co-Authors: Watanabe TerukiAbstract:Electron-deficient isothioureas tethered to vinyl tertiary N-heterocycles can afford carbodiimides upon desulfurization with thiophilic metals and non-nucleophilic amine bases. Addition of the N-heterocycles to the carbodiimdes form zwitterionic spiro-cycles which then undergo zwitterionic 1,3-diaza-Claisen rearrangements to afford guanidine containing macro-cycles. Variation of the N-heterocycles and the tether lengths influences the different reactivity in the rearrangement. Solvent effect and stereoselectivity are also explored. The method provides easy access to novel Guanidines that would be difficult to synthesize through conventional pathways
Ulf Berg - One of the best experts on this subject based on the ideXlab platform.
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new approach to biomimetic transamination using bifunctional 1 3 proton transfer catalysis in thioxanthenyl dioxide imines
Journal of Organic Chemistry, 2002Co-Authors: Anders Hjelmencrantz, Ulf BergAbstract:A pyridoxamine equivalent, 9-aminothioxanthene 10,10-dioxide, has been designed that is capable of affording transamination in good to excellent yields of natural as well as artificial amino acids. Amidines and Guanidines in catalytic amounts were capable of performing [1,3]-proton transfer in the imines under mild conditions, whereas various simple amines failed. The use of chiral catalysts resulted in modest asymmetric induction (ee ≤ 45%). The electronic dependence in para-substituted phenyl glyoxylate imines, isotope effects, and computational studies support a stepwise, bifunctional mechanism for amidine and guanidine catalysts. Attempts toward an autocatalytic model system are described.
