- Versatile Cp*Co(III)(LX) Catalyst System for Selective Intramolecular C-H Amidation Reactions
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Herein, we report the development of a tailored cobalt catalyst system of Cp*Co(III)(LX) toward intramolecular C-H nitrene insertion of azidoformates to afford cyclic carbamates. The cobalt complexes were easy to prepare and bench-stable, thus offering a convenient reaction protocol. The catalytic reactivity was significantly improved by the electronic tuning of the bidentate LX ligands, and the observed regioselectivity was rationalized by the conformational analysis and DFT calculations of the transition states. The superior performance of the newly developed cobalt catalyst system could be broadly applied to both C(sp2)-H and C(sp3)-H carbamation reactions under mild conditions.
- Chang, Sukbok,Jung, Hoimin,Kim, Dongwook,Lee, Jeonghyo,Lee, Jia,Park, Juhyeon
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supporting information
p. 12324 - 12332
(2020/08/06)
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- Synthesis of novel L-series 2',3'-dideoxy-3'-hydroxy-methyl-nucleosides and a convenient method for the separation of nucleoside anomers
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Photoinduced addition of methanol to 5(R)-(tert- butyldimethylsilyloxymethyl) -2(5H)-furan-2-one (derived from L-gulono-1,4- lactone) provided the photoadduct 5(R)-(tert-butyldimethylsiloxymethyl)- 4(S)-hydroxymethyl-tetrahydrofuran-2-one, which was converted into two L- series-2',3'-dideoxy-3'-hydroxymethyl-nucleosides. In addition, we describe a new method for the chromatographic separation of cytidine anomers using a N- 2-(4-nitrophenyl)ethyl carbamate derivative.
- Gould, Jayne H.M.,Mann, John
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p. 193 - 213
(2007/10/03)
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- Chemical compounds
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A novel class of protecting compounds, particularly for amino acids, is based on 2,2 di nitrophenyl ethan- groups, particularly the groups wherein the nitro is in the para position. The ethyl group may be substituted, e.g. by an alkyl group, in the l- position. Preferred compounds include the alcohol or halide which are suitable for protecting acid functional groups, and esters, including activated and substituted esters, particularly the succinimidyl ester, for protecting amine groups. The invention includes methods of manufacture and use, together with protected amino acids.
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- THE p-NITROPHENYLETHYL (NPE) GROUP. A VERSATILE NEW BLOCKING GROUP FOR PHOSPHATE AND AGLYCONE PROTECTION IN NUCLEOSIDES AND NUCLEOTIDES
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The syntheses of new monomeric building blocks for oligonucleotide synthesis via the phosphotriester approach containing the p-nitrophenylethyl group for phosphate and aglycone protection are described.Blocking of the amide function in guanosines at O6 can be achieved by the Mitsunobu reaction forming the corresponding O6-p-nitrophenylethyl derivatives (4,5,10).Sugar-protected thymidine (16) and uridine (17) have been alkylated at O4 in an SN1-type reaction by p-nitrophenylethyl iodide-silver carbonate in benzene to form the O4-p-nitrophenylethyl derivatives (18,19).Protection of the amino group in 2'-deoxycytidine (25) and cytidine (26) can be performed directly by 1-(p-nitrophenylethoxycarbonyl)-benzotriazole in DMF to obtain the corresponding carbamates (27,28) as a new type of N4-acylated cytidine derivative. p-Nitrophenylethoxycarbonylation of the amino group in 2'-deoxyadenosine (33) and adenosine (34) requires previous sugar protection by acyl or silyl groups and can then be achieved by p-nitrophenylethyl chloroformate or better by 1-methyl-3-p-nitrophenylethoxycarbonylimidazolium chloride to form N6-p-nitrophenylethoxycarbonyladenosines (38,39,40,42).The various p-nitrophenylethyl blocking groups are stable under mild hydrolytic conditions (e.g. ammonia and triethylamine) but can be cleaved selectively by DBU or DBN in aprotic solvents. 5'-O-Monomethoxytritylation (12,29,43) as well as phosphorylations at the 3'-OH group can be effected to give the corresponding 3'-(2,5-dichlorophenyl,p-nitrophenylethyl)-phosphotriesters (13,22,30,44) also in high yields.Oximate cleavage of the latter compounds to the phosphodiesters (14,24,32,46) and detritylation to the 5'-unblocked phosphotriesters (15,23,31,45) do not affect the aglycone protecting groups, thereby demonstrating their general versatility.The newly synthesized compounds have been characterized on the basis of their elementary analyses (C,N,H), and UV- and 1H-HMR-spectra.
- Himmelsbach, Frank,Schulz, Bernd S.,Trichtinger, Thomas,Charubala, Ramamurthy,Pfleiderer, Wolfgang
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- THE USE OF THE p-NITROPHENYLETHOXYCARBONYL GROUP FOR AMINO PROTECTION IN CYTIDINE AND ADENOSINE CHEMISTRY
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Amino protection in 2'-deoxycytidine (1) and cytidine (2) as well as in 2'-deoxyadenosine (8) and adenosine (9) respectively can be achieved by the new reagents 1-(p-nitrophenylethoxycarbonyl)-benzotriazole (3) and 1-methyl-3-(p-nitrophenylethoxycarbonyl)-imidazolium chloride (7) to from the corresponding carbamates (4, 5, 13, 14) in high yields.
- Himmelsbach, Frank,Pfleiderer, Wolfgang
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p. 3583 - 3586
(2007/10/02)
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