共查询到20条相似文献,搜索用时 15 毫秒
1.
Ramapanicker Ramesh 《Tetrahedron》2007,63(37):9153-9162
The base catalyzed cyclization of N-aryl and N-alkyl-O-propargyl carbamates is studied in detail. The effect of various bases and solvents on the efficacy of this cyclization reaction is analyzed and a new base-solvent system (LiOH in DMF) for effective cyclization of these carbamates is reported. A number of differentially substituted O-propargyl carbamates were cyclized to the corresponding 2-oxazolidinones under these conditions. The reaction conditions reported here are mild and no side reactions were observed in any of the substrates studied. A propargyl carbonate group was unaffected during the course of the cyclization of the O-propargyl carbamate group. The propargyl carbamates were prepared from the corresponding alkyl or aryl amines and the corresponding propargyl chloroformate, resulting in oxazolidinones diversely substituted at the nitrogen atom. N-Aryl-O-propargyl carbamates cyclized readily to the corresponding oxazolidinones with LiOH in DMF, whereas N-alkyl-O-propargyl carbamates reacted slowly under the same conditions. O-Propargyl carbamates substituted at the 1-position tend to cyclize faster whereas those substituted at 3-position cyclize considerably slower than the unsubstituted carbamates. 相似文献
2.
(E)-O-Arylsulfonyl-N-(2-nitroalk-2-enyl)hydroxylamines were easily obtained in good yields starting from (E)-nitro allylic alcohols, the crucial step being an inorganic base-catalyzed decarboxylative rearrangement of proposed labile unsaturated carbamates. A possible mechanism for the outcome of the reaction, characterized by the unusual retention of the sulfonyloxy group, is proposed. 相似文献
3.
Jean-Michel Vatèle 《Tetrahedron》2004,60(19):4251-4260
Prenyloxycarbonylimidazole (PreocIm) and prenyl p-nitrophenyl carbonate (PreocOC6H4p-NO2), two substitutes for the unstable prenyl chloroformate, allowed an efficient introduction of the prenyloxycarbonyl group to a variety of primary and secondary amines. Deprotection of prenyl carbamates was readily achieved by, first their conversion to 2-iodo-3-methoxy-3-methylbutyl carbamates with iodine in methanol followed by reductive β-elimination with zinc powder. These reaction conditions are compatible with the presence of a number of functional groups such as Boc and Cbz carbamates, sulfides, double bonds, indoles and aromatic ethers. 相似文献
4.
An efficient direct benzylic C-H amination via dehydrogenative-coupling by using an inexpensive catalyst/oxidant (CoBr2/tBuOOtBu) system is described. Various unmodified amides including primary or secondary sulfonamides, carboxamides, and carbamates preformed well with benzylic hydrocarbons with moderate to good yields. 相似文献
5.
The action of F-alkylated (alkylamino)ethanols on alkoxy- and aroxy-sulfonyl isocyanates allowed the preparation of the corresponding carbamates. The reaction occurred rapidly with good yields. 相似文献
6.
A series of 3-(N-substituted)-aminoquinolin-2(1H)-ones have been synthesized by the palladium-catalyzed C-N coupling reaction starting from 3-bromoquinolin-2-(1H)-ones. Various nucleophiles including amines, amides, sulfonamides, carbamates and ureas have been used successfully. In all the cases, the reactions take place rapidly in 1,4-dioxane and proceed in good to excellent yield using palladium acetate as a catalyst, Xantphos as a ligand and Cs2CO3 as a base. 相似文献
7.
Jan Pícha 《Tetrahedron letters》2008,49(28):4366-4368
The synthesis of norleucine-derived phosphonopeptides was achieved by BOP-catalyzed coupling of the monobenzyl ester of a N-CBz-protected phosphonate derivative of norleucine with hydroxyl moieties of derivatized lactic or glycolic acids. The complete deprotection of the product esters/carbamates was achieved in good yields by one-step Pd-catalyzed hydrogenolysis. 相似文献
8.
The conversion of carbamates into ureas using aluminum amide complexes is reported. This reaction is a convenient method to prepare bi-, tri- and tetra-substituted ureas from carbamate-protected primary or secondary amines by reaction with primary or secondary amines in the presence of stoichometric quantities of trimethylaluminum. A reactivity trend of the various carbamates was observed and methyl and benzyl carbamates were reacted selectively in the presence of t-butyl carbamates. 相似文献
9.
Claudia Feberero Cintia Virumbrales Carlos Sedano Lorena Renedo Samuel Surez-Pantiga Roberto Sanz 《Molecules (Basel, Switzerland)》2022,27(2)
A straightforward and transition metal-free one-pot protocol to synthesize halobenzo[b]furans has been developed employing simple and easily available starting materials such as O-aryl carbamates and alkynylsulfones. The fine-tuning of the different steps involved was key to achieving a successful one-pot procedure. Initially, a directed ortho-lithiation process, which uses the carbamate as the directed metalation group, was crucial in providing access to O-2-alkynylaryl N,N-diethyl carbamates by a direct alkynylation of the o-lithiated carbamate, with arylsulfonylalkynes as electrophilic reagents. Cyclization of the generated o-alkynylaryl carbamates was successfully accomplished through a strategy involving in situ carbamate alkaline hydrolysis under conventional heating or microwave irradiation, coupled with a subsequent heterocyclization step delivering the desired benzo[b]furans. A wide variety of new halobenzo[b]furans has been synthesized and their utility has been demonstrated by their further transformation. 相似文献
10.
Srinivasarao V. Narina 《Tetrahedron letters》2007,48(1):65-68
An efficient enantioselective synthesis of (−)-cytoxazone (1) and (+)-epi-cytoxazone (2) using proline-catalyzed asymmetric α-amino-oxylation of aldehydes followed by Rh-catalyzed diastereoselective oxidative C-H amination as the key steps is described. syn or anti 1,2-aminoalcohols were obtained by Rh-catalyzed intramolecular amidation of the C-H bonds of carbamates or sulfamate esters with good to excellent diastereoselectivity. 相似文献
11.
Condensation of methyl (3-hydroxyphenyl)carbamate with ethyl acetoacetate and ethyl benzoylacetate at room temperature, as well as with L-2-hydroxysuccinic acid on heating, in the presence of concentrated sulfuric acid gave the corresponding methyl (4-R-2-oxo-2H-chromen-7-yl)carbamates (R = Me, Ph, H). Condensation of methyl (3-hydroxyphenyl)carbamate with benzylidenemalononitrile or with aromatic aldehydes and malononitrile on heating in propan-2-ol in the presence of piperidine led to the formation of the corresponding methyl (4-aryl-2-amino-3-cyano-4H-chromen-7-yl)carbamates. 相似文献
12.
Prof. Arun K. Ghosh Amartyo J. Basu Dr. Che-Sheng Hsu Monika Yadav 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(43):e202200941
Asymmetric 1,2-carbamoyl rearrangement of lithiated 2-alkenyl carbamates has been investigated. Deprotonation of chiral 2-alkenyl oxazolidine carbamates with sec-butyllithium in ether at −78 °C followed by warming of the resulting 1-lithio-2-alkenyl derivatives to room temperature resulted in 1,2-carbamoyl rearrangement to provide α-hydroxy amides. The rearrangement proceeded with excellent diastereoselectivity and in good to excellent isolated yield of the α-hydroxy amide derivatives. The substrate scope of the reaction was investigated with a variety of 2-alkenyl and benzyl oxazolidine carbamates. A stereochemical model is provided to explain the stereochemical outcome associated with the rearrangement. Acid-catalyzed removal of the chiral oxazolidine afforded α-hydroxy acid in high optical purity. 相似文献
13.
We have developed an efficient one-pot method for the microwave-assisted synthesis of ureas and carbamates via a proposed Lossen rearrangement. Herein we report the first examples of the direct conversion of benzoyl chlorides into N,N′-disubstituted ureas and N-aryl carbamates using hydroxylamine-O-sulfonic acid as reagent. Using our general method, we have produced 11 examples of N,N′-disubstituted phenylureas in yields up to 95% using various substituted anilines, and primary and secondary amines. Additionally, we were able to generate a series of N-aryl carbamates in moderate yields using primary, secondary and tertiary alcohols. 相似文献
14.
《Tetrahedron: Asymmetry》1999,10(18):3467-3471
The reaction of cyclic ketones with tert-butyl or benzyl carbamate under acidic conditions directly affords prochiral ene carbamates. Their enantioselective hydrogenation in the presence of a chiral ruthenium catalyst provides a new access to optically active carbamates easy to deprotect to the corresponding optically active amines. 相似文献
15.
Akio Saito Manabu Tojo Hikaru Yanai Fukiko Wada Muga Nakagawa Midori Okada Azusa Sato Rieko Okatani Takeo Taguchi 《Journal of fluorine chemistry》2012
CrCl2/Mn-mediated transformation of various dibromofluoromethylcarbinyl esters including carboxylates, carbonates and carbamates provided 1-fluoro-1-alkenyl esters via [2,3]-sigmatropic rearrangement of ester group. Reaction proceeded by using CrCl2/Mn system under mild conditions (in THF at room temperature) to give 1-fluoro-1-alkenyl esters in good yield with an excellent Z selective manner. 1-Fluoro-1-alkenyl ester thus obtained acts as a double acyl donor in the reaction with necleophiles such as amine, thiol, alcohol as well as bifunctional necleophiles such as ethylene diamine derivative. 相似文献
16.
Halocyclocarbamation of benzyl N-(1-phenyl-3-butenyl)carbamates afforded 6-functionalized 4-aryl-1,3-oxazinan-2-ones with moderate to excellent diastereoselectivity depending on the N-substituent. Importantly, in contrast to reported cyclocarbamations of homoallylic carbamates, which are generally trans-diastereoselective, cyclization of N-unsubstituted Cbz-protected homoallylamines led to cis-1,3-oxazinan-2-ones, predominantly. The use of N-benzylated and in situ prepared N-silylated derivatives resulted however in trans-selectivity. Transition states are proposed to explain the stereochemical influence of the N-substituent on the cyclocarbamations. The functionalized 1,3-oxazinan-2-ones could be further elaborated towards biologically or synthetically important 6-arylpiperidine-2,4-diones and 3-aryl-1,3-aminoalcohols. 相似文献
17.
The reaction of ortho-alkynylphenylureas 1 having a carbamoyl group attached to the nitrogen atom proceeded in the presence of catalytic amounts of PtI4, affording corresponding indole-3-carbamides 2 in moderate to high yields. In addition, the platinum-catalyzed cyclization of ortho-alkynylphenyl carbamates 3 afforded corresponding indole-3-carboxylates 4 in good yields. The present reaction proceeds through the intramolecular addition of carbon-nitrogen bonds to triple bonds, the so-called carboamination. 相似文献
18.
The lithiodestannylation and intramolecular anti-selective carbolithiation of α-lithiated ω-carbamoyloxy-1-alkynyl carbamates have been used to synthesize highly enantioenriched protected 2-alkylidene-cycloalkane-1,3-diols. 相似文献
19.
Synthesis of a N-Boc-protected piperidin-2-yl phosphine oxide starting from piperidine in three steps, followed by olefination using a variety of α,β-unsaturated aldehydes resulted in tert-butyl 2-(2′-alkenylidene)piperidine-1-carboxylates in high yields. A novel type of intramolecular cyclization of these enamides furnished a new family of 3-alkyl-4,6,7,8-tetrahydro-3H-pyrido[1,2-c][1,3]oxazin-1-ones as useful substrates for further elaboration. Subsequent reduction of these unsaturated bicyclic carbamates using NaCNBH3 or NaBH4 afforded the corresponding 3-alkylhexahydropyrido[1,2-c][1,3]oxazin-1-ones in a highly stereoselective way. Reductive ring opening of two representatives furnished the corresponding Sedum alkaloid derivatives in good yields. 相似文献
20.
Anatoly D. Shutalev Anastasia A. Fesenko Olesya M. Kuzmina Alexander N. Volov Dmitry V. Albov Vladimir V. Chernyshev Ilia A. Zamilatskov 《Tetrahedron letters》2014
An efficient method for the stereoselective synthesis of novel 14-membered cyclic bis-semicarbazones based on acid-catalyzed cyclization of the hydrazones of 3-(3-oxobutyl)semicarbazides has been developed. The starting semicarbazides were prepared according to a four-step strategy involving amidoalkylation of the sodium enolate of acetylacetone with N-(α-tosylbenzyl)carbamates followed by base-promoted retro-Claisen reaction and treatment of the obtained N-(3-oxobutyl)carbamates with hydrazine. 相似文献