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1.
Reaction of N-tosyl aziridines with nitric oxide affords the corresponding ring-opened products in regio-, stereoselectivities and excellent yields.  相似文献   

2.
Direct conversion of epoxides to aziridines was achieved with guanidines as a nitrogen source. Stereochemical inversion at the chiral centers of epoxides was observed without loss of optical purity.  相似文献   

3.
The reactions of 3,4-epoxytetrahydropyran and of its cis- and trans-2-methyl derivatives with hydrogen halides and with lithium aluminum hydride have been investigated in order to assess the influence of an O atom in the β position on the regioselectivity of the epoxide ring opening. All these reactions exhibit a high preference for nucleophilic attack at position 4, which decreases moderately only when the inductive effect of the O atom and the stereoelectronic requirements of the attack act in opposite directions. Similar trends are observed in the reactions of the 5,6-dihydro-2H-pyrans with NBA, which occur with preferential nucleophilic attack by water at position 4 of the intermediate epibromonium ions. A remarkably high preference (96%) for electrophilic attack syn to the 2-Me group is observed in the latter type of reaction, in accordance with a previous proposal of a mechanism in which the nucleophilic step is rate determining.  相似文献   

4.
A conceptually new, simple and practical method for the syn-nucleophilic displacement of aryl and vinyl epoxides and aryl aziridines with (substituted) phenols, using aryl borates as activating nucleophiles under neutral conditions, is reported.  相似文献   

5.
Epoxides and aziridines undergo ring-opening readily with NaN3 in the presence of ammonium-12-molybdophosphate to afford the corresponding 2-azidoalcohols and 2-azidoamines in high yields with good regio- and stereoselectivity under mild reaction conditions.  相似文献   

6.
Epoxides and aziridines undergo ring opening efficiently with (bromodimethyl)sulfonium bromide at room temperature to form the corresponding β-bromohydrins and β-bromoamines, respectively. The conversions are highly regioselective and afford the products in excellent yields within a short period of time.  相似文献   

7.
The regio- and stereoselective ring opening of vinyl epoxides has been achieved by the use of Lewis acid, MgBr2, affording bromohydrins in excellent yield, which are readily transformed to azidoalcohol, a key intermediate of several classes of pyrrolizidine and indolizidine alkaloids. The scope and limitations of the reaction are discussed.  相似文献   

8.
The addition of primary and secondary aliphatic amines to glycal-derived allyl epoxides is completely 1,2-regio- and anti-stereoselective, whereas mixtures of the corresponding anti-1,2- [3-N-(substituted-amino) glycals] and anti-1,4-addition products (N-glycosyl amines) are obtained with N-(mesyl)-aziridines. In this way, structural moieties, otherwise difficult to synthesize, are obtained by means of a very simple protocol. The regio- and stereoselectivity observed with epoxides is the consequence of an isomerization process, whereas the result obtained with aziridines is explained by the absence of an effective substrate-nucleophile (amine) coordination.  相似文献   

9.
The cycloaddition of (Z)-7-(prop-1-enyl)-7-azabicyclo[4.1.0]heptane with dimethyl acetylene dicarboxylate (DMAD) was reported previously to proceed with complete stereoselectivity. Quantum chemical calculations (B3LYP) were used to evaluate the mechanism of the cyclization process, and it was discovered that a stepwise pathway is preferred. The subsequent electrocyclic ring opening reaction of the cyclobutene was also studied, and it was found that ring opening to the "methyl-in" dienamine is preferred to the "methyl-out" product by some 4-5 kcal/mol.  相似文献   

10.
C-Amidonitrones add regio- and stereoselectively to esters of 3-methylenecyclopropane-1,2-dicarboxylic, 2-(diphenylmethylene)cyclopropane-1,1-dicarboxylic, and 2-(1-phenylethylidene)cyclopropane-1,1-dicarboxylic acids to form a single diastereomer of 4-spirocyclopropaneisoxazolidines.  相似文献   

11.
Regio- and stereoselectivity of 1,3-dipolar cycloaddition of cyclic aldonitrones of the 3-imidazoline 3-oxide series mainly depends on the type of the substituent in the dipolarophile. The configuration of the main cycloadduct has been determined, and a method has been suggested to establish the stereochemistry of the cycloaddition products by1H NMR spectroscopy. An increase in electron-acceptor properties of the substituent in the alkene molecule results in a decrease in the regio- and stereoselectivity of the cycloaddition.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 894–898, May, 1994.  相似文献   

12.
Epoxides and aziridines are cleaved efficiently and regioselectively in the presence of zirconyl nitrate at room temperature to afford the corresponding β-nitrato-alcohols and -sulfonamides, respectively, in high yields.  相似文献   

13.
Upon epoxidation with dimethyldioxirane, the 2',5'-bis-O-silyl derivatives of 9-(3-deoxy-beta-D-glycero-pent-3-enofuranosyl)adenine gave the respective "3',4'-up" epoxides exclusively. Reaction between these epoxides and Me3Al was investigated in detail. It was found that the stereoselectivity of epoxide ring opening (anti versus syn) varied significantly upon changing the amount of Me3Al, the solvent, the O-silyl protecting group, and the reaction temperature. A possible reaction mechanism is proposed.  相似文献   

14.
Epoxides can be opened under neutral conditions with TMSN3 and TMSCN in the presence of catalytic amounts of Lewis acid, affording the corresponding ring-opened compounds in high yields.  相似文献   

15.
The reactions of some organocopper reagents with cyclic 2-alkenyl aziridines were examined. The stereoselectivity of the addition reaction of dialkylzinc can be strongly influenced by the use of phosphoramidites as ligands for copper. Chiral copper complexes of 2,2′-binaphthyl-based phosphoramidites were shown to be highly effective catalysts for the regio- (SN2′) and anti-stereoselective addition of dialkylzinc reagents to these compounds according to a kinetic resolution protocol. The corresponding new cyclic allylic amine reaction products were obtained with a good enantioselectivity (83% ee).  相似文献   

16.
A new entry to optically pure trans-2,3-disubstituted N-sulfinyl aziridines starting from 1,2-aminosulfides, involving formation of a sulfonium salt intermediate followed by intramolecular nucleophilic attack by the sulfinamide nitrogen atom, is reported. The regio- and stereoselective opening of the aziridine ring can be achieved by anchimeric assistance of the sulfinyl group.  相似文献   

17.
Di- and trisubstituted steroidal epoxides are shown to be converted smoothly to halohydrins in high yield by triphenylphosphine-halogen complexes, under non-acidic and non-eliminating conditions.  相似文献   

18.
The review summarizes methods for the synthesis of 1,3-oxazolidin-2-ones, 1,3-oxazolidines, and dihydro-1,3-oxazoles from epoxides and aziridines. Possible applications of N,O-containing heterocycles in medicinal and organic chemistry as biologically active substances and intermediate products for their preparation are considered.  相似文献   

19.
The stereospecific and regioselective C(3) alkynylation of trisubstituted epoxides has been achieved with lithium alkynyl trimethylaluminium ate complexes in the presence of BF3 x OEt2.  相似文献   

20.
The regio- and stereoselectivity of the reactions of carbanions, generated from alkanals, carboxylates of the type XYCHCOOEt (X = EtOOC, CN, Ac; Y = H, Br), or derivatives of 3-methyl-4-phosphono-2-butenoic acid using PTC techniques, with aldehydes of various types (alkanals, ,-enals, cross-conjugated enedials, benzaldehydes,etc.) are reviewed. The factors affecting the outcome of these reactions are discussed. The carbanion analogs, triphenylphosphorus ylides, are shown to attack selectively at one of the aldehyde groups of aromatic dialdehydes. The regularities found for the title reactions were used in the syntheses of some biologically active isoprenoids.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1867–1885, October, 1995.  相似文献   

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