ZrCl4 as a new and efficient catalyst for the opening of epoxide rings by amines

Zirconium(IV) chloride catalyses the nucleophilic opening of epoxide rings by amines leading to the efficient synthesis of β-amino alcohols. The reaction works well with aromatic and aliphatic amines in short times at room temperature in the absence of solvent. Exclusive trans stereoselectivity is observed for cyclic epoxides. Aromatic amines exhibit excellent regioselectivity for preferential nucleophilic attack at the sterically less hindered position during the reaction with unsymmetrical epoxides. However, in case of styrene oxide, selective formation of the benzylic amine was observed during the reactions with aromatic amines.     

1,2,3,4-Tetrahydro-γ-carbolinium salts: novel reactions with thiols, mediated by polymer-supported reagents

A series of dialkyl-[2-(3-alkylsulfanylmethyl-1H-indol-2-yl)-ethyl]amines was produced using a novel route involving nucleophilic ring opening of 2,2-dialkyl-1,2,3,4-tetrahydro-γ-carbolinium salts with thiols. The insertion reaction was mediated by a strong, polymer-supported base, and the purification of the target compounds was facilitated using resin-bound sulfonic acid.     

Réactivité des cinnamoyl-3 pyrones-2 vis à vis des amines primaires

The reaction of primary amines (methylamine, isopropylamine, benzylamine) in neutral medium, on 3-cinnamoyl-2-pyrones gave 7-amino-3,5-dioxo-l,6-octadienes 2 . The formation of these compounds is presumed to occur via nucleophilic attack of amines with a ring opening reaction followed by decarboxylation. Their structures were determined unambiguously by ¹H, ¹³C nmr spectroscopy, elemental analysis and mass spectrometry.     

Scope and limitations of montmorillonite K 10 catalysed opening of epoxide rings by amines

Montmorillonite K 10 efficiently catalyses the opening of epoxide rings by amines in high yields with excellent regio- and diastereo-selectivities under solvent-free conditions at room temperature affording an improved process for synthesis of 2-amino alcohols. Reaction of cyclohexene oxide with aryl/alkyl amines leads to the formation of trans-2-aryl/alkylaminocyclohexanols. For unsymmetrical epoxides, the regioselectivity is controlled by the electronic and steric factors associated with the epoxide and the amine. Selective nucleophilic attack at the benzylic carbon of styrene oxide takes place with aromatic amines, whereas, aliphatic amines exhibit preferential nucleophilic attack at the terminal carbon. Aniline reacts selectively at the less hindered carbon of other unsymmetrical epoxides. The difference in the internal strain energy of the epoxide ring in cycloalkene oxides and alkene oxides led to selective nucleophilic opening of cyclohexene oxide by aniline in the presence of styrene oxide. Due to the chelation effect, selective activation of the epoxide ring in 3-phenoxy propylene oxide takes place in the presence of styrene oxide leading to preferential cleavage of the epoxide ring in 3-phenoxy propylene oxide by aniline.     

An unusual Mannich type reaction of tertiary aromatic amines in aqueous micelles

An efficient, unusual Mannich type reaction of tertiary aromatic amines, formaldehyde and 1,3-dicarbonyl compounds is described in aqueous micelles catalyzed by boric acid to afford dialkylaminoarylated 1,3-dicarbonyls. In this unusual Mannich type reaction, tertiary aromatic amines react with formaldehyde to generate an N-alkyl-N-(4-methylenecyclohexa-2,5-dienylidene)alkylaminium intermediate (aza quinone methide), which undergoes nucleophilic addition with 1,3-dicarbonyl compounds. The reaction is highly regioselective, and exclusively para functionalized products are formed in high yields.     

Synthesis of Complex Diarylamines through a Ring-Opening Difunctionalization Strategy**

The diarylation and skeletal diversification of unstrained cyclic amines was exploited to expand and modify the favorable properties of this important substrate class with pivotal roles in drug discovery. Cyclic amines were employed in the synthesis of a novel class of amino-substituted diaryliodonium salts, which were converted to highly functionalized diarylamines through an atom-efficient one-pot N-arylation/ring opening reaction with external nucleophiles. The reaction proceeds through in situ formation of a diarylammonium intermediate that undergoes a nucleophilic ring opening by cleavage of the strong C−N bond. A wide variety of diarylamines was obtained through introduction of two different aryl groups of varied electronics, and the retained iodo-substituent enables downfield diversifications of the products. More than 20 nucleophiles, including amines, phenols, carboxylic acids, thiols and halides, were alkylated with high functional group tolerance, and the strategy proved efficient also in in late-stage functionalization of natural products and pharmaceuticals.     

Transformations of 5,6,7,8-tetrafluoro-2-ethoxycarbonylchromone under the action of primary amines

5,6,7,8-Tetrafluoro-2-ethoxycarbonylchromone in aprotic polar solutions formed by nucleophilic aromatic ipso-substitution 7-alkyl(aryl)amino-5,6,8-trifluorochromones. This transformation in ethanol depended on the reactivity of the acting amine: with stronger nucleophiles, aliphatic amines, an opening of the γ-pyrone ring occurred, with aromatic amines 7-monosubstituted chromones were the main products, and the open-chain esters formed in lesser amount.     

The mechanism of N-haloamide promoted electrophilic additions. high regio and stereoselectivity in the conversion of 2-tert-butyl-3,6-dihydro-2H-pyran into bromohydrins and in the opening of the corresponding epoxides

The reactions of cis- and trans-2-tert-butyl-4,5-epoxytetrahydropyran with HBr and with LAH have been examined as a model for the nucleophilic step of the reaction of the corresponding olefin with NBA in aqueous dioxane. A remarkable 90:10 preference for electrophilic attack syn to the tert -butyl group in the NBA reaction is found and shows that the two epoxides, as well as the intermediate epibromonium ions, undergo nucleophilic attack with high preference for diaxial opening, even when this requires reaction at carbon 5, which is more subject than carbon 4 to the unfavourable inductive effect of the pyran ring oxygen. These results constitute a further proof in favour of a mechanism of N-haloamide promoted electrophilic additions in which the electrophilic step is rapidly reversible and product composition is determined during the nucleophilic step.     

Stereoselective tribromomethylation of N-(tert-butanesulfinyl)imines with bromoform: practical synthesis of α-tribromomethyl amines

The unprecedented nucleophilic tribromomethylation of N-(tert-butanesulfinyl)imines with bromoform has been shown to be a highly stereoselective and practical method for the synthesis of enantiomerically pure α-tribromomethyl amines. THF has proven to be the best solvent in this addition reaction. By changing the reaction solvent from THF to DMF, 2,2-dibromoaziridines can also be synthesized directly from bromoform and N-(tert-butanesulfinyl)imines under similar reaction conditions.     

Traceless solid-phase synthesis of 2,4,6-chlorodiamino and triaminopyrimidines

An effective traceless solid-phase synthesis of chloro-diaminopyrimidines via an amino-de-chlorination reaction of polymer-bound 4-alkoxycarbonylamino-2,6-dichloropyrimidines has been developed. After release from the polymer the target molecules were obtained in good to excellent purity, although with modest regiocontrol. Further reaction of solid-supported N-alkoxycarbonyl-chloro-diaminopyrimidines with secondary amines afforded triaminopyrimidines in good purity under mild conditions, whereas less nucleophilic primary amines did not perform well under the conditions explored so far.     

Development of one-pot benzylic amination reactions of azine N-oxides

An efficient one-pot synthetic methodology has been developed for the benzylic amination reactions of methyl-substituted azine N-oxides that operate under mild conditions. The reaction was found to tolerate quinoline and isoquinoline N-oxides with electron donating and withdrawing substituents as the electrophilic reaction partners as well as a broad range of nucleophilic primary, secondary and aromatic amines, affording the benzylic amination products in up to 82% yield.     

Ring-Enlargement and Ring-Opening Reactions of 1,2-Thiazetidin-3-one 1,1-Dioxides with Ammonia and Primary Amines as Nucleophiles

The N-benzyl- and N-alkyl-substituted 1,2-thiazetidin-3-one 1,1-dioxides 1b – d reacted readily with NH₃ and primary amines via ring opening. The reaction with NH₃ proceeded at −78°→room temperature yielding ring-opened adducts via nucleophilic attack of NH₃ at the sulfonyl group, whereas the reactions with amines at room temperature yielded products via attack at the carbonyl group. The N-unsubstituted analogue 1a , when reacted with benzylamine in refluxing EtOH, also gave a product of ring opening via nucleophilic attack at the carbonyl group of 1a . The transamidation-like reactions of the 2-(aminoalkyl)-1,2-thiazetidin-3-one 1,1-dioxides 19a – d proceeded via six-, seven-, and eight-membered intermediates, giving the ring-enlarged eight-, nine-, and ten-membered products 21 – 24 (Schemes 8 and 9), respectively, in 42 – 87% yields. The products resulted from the nucleophilic attack of the amino group of the side chain at the carbonyl C-atom. The structure of the eight-membered product 24 with an asymmetrically situated methyl substituent was established by X-ray crystallography.     

Nucleophilic alkynylation of N-bis(trimethylsilyl)methyl aldimines

N-Bis(trimethylsilyl)methyl aldimines undergo nucleophilic addition reaction with premixed lithium alkynides/BF₃·OEt₂ to give moderate to good yields of N-bis(trimethylsilyl)methyl propargyl amines.     

“One pot” synthesis of tertiary amines: Ru(II) catalyzed direct reductive N-benzylation of imines with benzyl bromide derivatives

The direct reductive N-benzylation of imines by reaction with benzyl bromide derivatives, in the presence of [RuCl₂(p-cymene)]₂ catalyst and PhSiH₃, is performed under mild conditions without additional base. This reaction proceeds by a tandem imine hydrosilylation/nucleophilic substitution with benzyl bromide derivatives to result the tertiary amines.     

Nucleophilic substitution in nitrofluorenones

The reaction of 2,4,5,7-tetranitrofluorenone with amines, thiols, and phenol in a polar aprotic solvent led to the preferable substitution of the nitro group in the position 2, and in the reaction of 2,4,7-trinitrofluorenone first the nitro group in the position 4 was replaced. The different regioselectivity is due evidently to the steric hindrances to the nucleophilic attack on the atom C⁴ caused by the nitro group in the position 5 of tetranitrofluorenone.     

Synthesis of 4-amino-1,2,3,4-tetrahydropyridine derivatives by intramolecular nucleophilic addition of tertiary enamides to in-situ generated imines

The reactivity of stable tertiary enamides in nucleophilic addition reaction with various in-situ generated imines was explored. Under very mild conditions, formyl-bearing tertiary enamides reacted with both aromatic and aliphatic amines to form imine intermediates. In the absence or presence of p-toluenesulfonic acid as a catalyst, intramolecular nucleophilic addition of enamide to imine functionality proceeded effectively to produce diverse 4-amino-1,2,3,4-tetrahydropyridine derivatives in good to excellent yields.     

Synthesis of pyrimidinyl arylglycines through subsequent Mitsunobu and Petasis reactions

The synthesis of highly functionalized pyrimidinyl arylglycines is presented. The highlight in our synthetic sequence includes selective O-alkylation of 2-(benzylsulfanyl)-4(3H)-pyrimidinones with N-Boc β-aminoalcohols under Mitsunobu conditions, Petasis reaction with glyoxylic acid and phenylboronic acid and nucleophilic ipso-substitution of the activated sulfur with morpholine. The unexpected spontaneous Smiles rearrangement of several pyrimidinyl amines is also discussed.     

Ring cleavage of dihydropyrimidine skeleton

The first observation of ring cleavage between positions 1 and 2 of a 1,4-dihydropyrimidine skeleton was reported upon the nucleophilic addition of 4,6-unsubstituted 1,4-dihydropyrimidine with 3 equiv of an aniline derivative or phenylhydrazine in the presence of 0.1 equiv of pyridinium p-toluenesulfonate (PPTS) in CH₂Cl₂; the nucleophilic reactions of 4-methyl-6-unsubstituted 1,6(3,4)-dihydropyrimidine with the same amines gave conventional substituted products at position 2. The effect of this ring opening was found to be due to the electron density of the benzene ring of a nucleophilic amine. On the other hand, aralkylamines, alkylamines, or heterocyclic amines did not cleave the skeleton. The ring-opening chemical structure was confirmed by X-ray crystallographic analysis. This characteristically different phenomenon may be due to the pattern of two CC double bonds of 1,4-DP and 1,6(3,4)-DP as well as to the effect of two substituted groups on the DP ring.     

Novel one pot synthesis of azolo[1,5-a]pyridines from Viehe’s salts

We have developed a practical procedure for the synthesis of polyfunctional azolo[1,5-a]pyridines via the reactive species generated in situ from N-substituted lactams and Viehe’s salt. The reaction is regioselective with respect to the nucleophilic addition of bis-anions derived from methyl azolyl acetates. The described protocol allowed for the introduction of three elements of diversity into the targeted molecules, including substituents originating from the (i) nucleophile input, (ii) lactam ring, and (iii) nucleophilic aromatic displacement (S_NAr) of the NMe₂ group with amines. A short reaction sequence, good yields of title compounds (44-69%), as well as their ready isolation, and purification are the distinct advantages of the reported protocol.     

Synthesis of chiral vicinal C2 symmetric and unsymmetric bis(sulfonamide) ligands based on trans-1,2-cyclohexanediamine by aminolysis of N-tosylaziridines

The ring opening of N-tosylaziridines with aliphatic amines can be efficiently catalyzed by lithium perchlorate to provide derivatives of the trans-1,2-diamine in high yields. The reaction was used in desymmetrization of several cyclic N-tosylaziridines using chiral amines. Using this strategy, an efficient synthesis of chiral vicinal C₂ symmetric bis(sulfonamide) and unsymmetrical bis(sulfonamide) ligands based on trans-1,2-cyclohexanediamine was developed.