- Enantioselective Synthesis of 5,5-Disubstituted Hydantoins by Br?nsted Base/H-Bond Catalyst Assisted Michael Reactions of a Design Template
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A new method for the enantioselective synthesis of 5,5-disubstituted (quaternary) hydantoins was developed on the basis of an organocatalytic Michael reaction approach involving the use of 2-benzylthio-3,5-dihydroimidazol-4-ones as key hydantoin surrogates. The method is general with respect to the substitution pattern at the hydantoin N1 (alkyl, aryl, acyl), N3 (aryl), and C5 (linear/branched alkyl, aryl) positions and affords essentially single diastereomeric products with enantioselectivities higher than 95 % ee in most cases. Among the bifunctional Br?nsted base/H-bond catalysts examined, a known squaramide–tertiary amine catalyst and a newly prepared squaramide–tertiary amine catalyst provide the highest selectivity so far with either nitroolefins or vinyl ketones as the acceptor components. Kinetic measurements support a first-order rate dependence on both reaction partners, the donor template and the Michael acceptor, whereas competitive 1H NMR spectroscopy experiments reveal the high ability of the template for catalyst binding.
- Izquierdo, Joseba,Etxabe, Julen,Du?abeitia, Eider,Landa, Aitor,Oiarbide, Mikel,Palomo, Claudio
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supporting information
p. 7217 - 7227
(2018/05/04)
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- Microwave assisted synthesis of 1,3,4-oxadiazole/thiohydantoin hybrid derivatives via dehydrative cycliztion of semicarbazide
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A series of compounds containing both 1,3,4-oxadiazole and thiohydantoin were synthesized as a promising scaffold for application in medicinal chemistry. The key step of the synthesis is a microwave-assisted cyclization of semicarbazides possessing a thiohydantoin moiety at one of the acyl termini using POCl3 as a dehydrating reagent. A wide range of semicarbazides were prepared through the substitution of hydrazides with an N-acylated thiohydantoin derived from the cyclization of the corresponding isothiocyanate with an amino acid and subsequent N-acylation of the resultant thiohydrantion. Consequently, the 58 number of 1,3,4-oxadiazole derivatives having a thiohydantoin substituent were prepared in good overall yields. Thiohydantoin 134-Oxadiazole Semicarbazide Microwave Amino acid Acknowledgments. This research was conducted under the Industrial Infrastructure Program for Fundamental Technologies and Institute for Advancement of Technology through the Inter-ER Cooperation Projects (R0002016) which are funded by the Ministry of Trade, Industry & Energy, Korea to YDG and Open Translational Research Center for Innovative Drug (2012M3A9C1053532) which are funded by National Research Foundation of Korea.
- Yang, Seung-Ju,Lee, Jae-Min,Lee, Gee-Hyung,Kim, NaYeon,Kim, Yong-Sang,Gong, Young-Dae
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supporting information
p. 3609 - 3617
(2015/02/05)
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- BASE CATALYZED CYCLIZATION OF SUBSTITUTED ESTERS OF HYDANTOIC AND THIOHYDANTOIC ACID
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Base catalyzed cyclization rates have been measured of 22 derivatives of hydantoic and thiohydantoic acid esters in water and methanol.The cyclization of methyl and ethyl esters of hydantoic and 5-methylhydantoic acids is accompanied by hydrolysis of the ester group, whereas with the other derivatives the hydrolysis does not take place.Hydrolysis of the cyclization products (hydantoin and thiohydantoin derivatives) is not significant under the kinetic conditions.The cyclization of methyl ester of 5-phenylhydantoic acid in methanol is reversible; the equilibrium mixture contains 30percent of the starting ester.In all the cases the cyclization is subject to specific base catalysis; exceptions are esters of 5-phenylthiohydantoic and 5-phenyl-2-methylthiohydantoic acids whose cyclizations are subject to general base catalysis.Substituents always accelerate the cyclization.The 3-substituents have the greatest effects, the cyclization rate being considerably increased with bulk of the substituents; similarly large effect of 5-phenyl group consists mainly in its polar effects on the pre-equilibrium.The cyclizations are slower in methanol at the same concentration of the lyate ion: the greatest difference (up to 3 orders of magnitude) is observed with the 5-phenyl derivatives.
- Kavalek, Jaromir,Machacek, Vladimir,Svobodova, Gabriela,Sterba, Vojeslav
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p. 375 - 390
(2007/10/02)
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- CHIRAL ANALYSIS OF THE REACTION STAGES IN THE EDMAN METHOD FOR SEQUENCING PEPTIDES
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Chiral isothiocyanate reagents suitable for 'Edman sequencing' have been synthesised and used to assess the chiral features of individual stages in the Edman method.Using h.p.l.c. analysis of the diastereoisomeric thiohydantoins obtained, it has been deduced that the cyclisation and cleavage of thiazolinone step is the likely source of racemisation of the chiral centre derived from the N-terminal amino acid.
- Davies, John S.,Mohammed, Karim A.
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p. 1723 - 1728
(2007/10/02)
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