Reactions of heterocyclic paramagnetic aldonitrone, 2,2,5,5-tetramethyl-3-imidazoline-1-oxyl 3-oxide, with alkynes

The reactions of heterocyclic paramagnetic aldonitrone,viz., 2,2,5,5-tetramethyl-3-imidazoline-1-oxyl 3-oxide, with mono- and disubstituted alkynes afford unstable isoxazoline derivatives. The reactions with monosubstituted alkynes yield predominantly 5-substituted regioisomers. The resulting isoxazoline derivatives are readily (and often spontaneously) converted into enaminoketones,viz, imidazolidine-1-oxyl derivatives. In the presence of tolan, the title paramagnetic aldonitrone gives a dimer in which one imidazoline ring undergoes profound transformation. The structure of the resulting dimer was established by X-ray diffraction analysis. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 112–117, January, 2000.     

Reactions of heterocyclic paramagnetic aldonitrone, 2,2,5,5-tetramethyl-3-imidazoline-1-oxyl 3-oxide, with alkynes

The reactions of heterocyclic paramagnetic aldonitrone,viz., 2,2,5,5-tetramethyl-3-imidazoline-1-oxyl 3-oxide, with mono- and disubstituted alkynes afford unstable isoxazoline derivatives. The reactions with monosubstituted alkynes yield predominantly 5-substituted regioisomers. The resulting isoxazoline derivatives are readily (and often spontaneously) converted into enaminoketones,viz, imidazolidine-1-oxyl derivatives. In the presence of tolan, the title paramagnetic aldonitrone gives a dimer in which one imidazoline ring undergoes profound transformation. The structure of the resulting dimer was established by X-ray diffraction analysis. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 112–117, January, 2000.     

Development of the Pictet-Spengler reaction catalyzed by AuCl3/AgOTf

Mild and efficient AuCl3/AgOTf-catalyzed Pictet-Spengler reactions were developed to afford in good yields a variety of tetrahydroisoquinoline and tetrahydro-beta-carboline ring systems, which constitute important motifs in biologically active natural and synthetic organic compounds.     

Application of 4,5-O,N-oxazolidinone protected thiophenyl sialosyl donor to the synthesis of α-sialosides

The synthesis of a novel oxazolidinone sialosyl donor is reported. The introduction of a trans-fused ring enhances reactivity and stereoselectivity in glycosylation reactions for the synthesis of α-sialosides. The oxazolidinone ring can also be removed under basic conditions to afford the deprotected amine, which can be further functionalized.     

Sels d'aziridinium stables,C-fonctionnalisés

Aziridines bearing a functionnality on a ring carbon have been treated with methyl fluorosulfonate to afford the corresponding aziridinium salts in high yields. These compounds were unambiguously characterised by the ring opening reactions using lithium chloride. Two quantitative methods for effecting counter-ion exchange are described.     

H3PW12O40催化水相介质中苯并恶嗪和喹唑啉合成（英文）简

A heteropolyacid efficiently catalyzed the cyclocondensation reaction of 2-aminobenzamide and salicylamide with aldehydes and ketones to afford good yields of benzoxazine and quinazoline ring systems in an aqueous medium. The method gives clean reactions, has simple workup procedure, and uses environment friendly conditions.     

1,4-pentadienyl-3-sulfonamides: frameworks for "disfavored" radical cascade cyclizations

[reaction: see text]. 1,4-pentadienyl-3-sulfonamides afford products including those resulting from disfavored 5-endo-trig reactions when subjected to radical cyclization conditions. Products resulting from pathways featuring 4-exo-trig cyclizations are also detected, even when the 4-exo-trig reaction leads to a highly strained bicyclo[3.2.0] ring system.     

Structurally Divergent Lithium Catalyzed Friedel–Crafts Reactions on Oxetan‐3‐ols: Synthesis of 3,3‐Diaryloxetanes and 2,3‐Dihydrobenzofurans

The first examples of 3,3‐diaryloxetanes are prepared in a lithium‐catalyzed and substrate dependent divergent Friedel–Crafts reaction. para‐Selective Friedel–Crafts reactions of phenols using oxetan‐3‐ols afford 3,3‐diaryloxetanes by displacement of the hydroxy group. These constitute new isosteres for benzophenones and diarylmethanes. Conversely, ortho‐selective Friedel–Crafts reactions of phenols afford 3‐aryl‐3‐hydroxymethyl‐dihydrobenzofurans by tandem alkylation–ring‐opening reactions; the outcome of the reaction diverging to structurally distinct products dependent on the substrate regioselectivity. Further reactivity of the oxetane products is demonstrated, suitable for incorporation into drug discovery efforts.     

Synthesis of 1,2,4-oxadiazines and their rearrangement to pyrimidines

Several amide oximes underwent condensation reactions with dimethyl acetylene dicarboxylate to afford 1:1 adducts. Under basic conditions, these adducts underwent ring closure to afford several methyl [3-(substituted)-4,5-dihydro-5-oxo-6H-1,2,4-oxadiazin-6-ylidene]acetates. The reactions of these compounds with a variety of amines resulted in addition-rearrangement reactions with the formation of the corresponding methyl 2-substituted-5-substituted amino-1,6-dihydro-6-oxo-4-pyrimidine carboxylates.     

Studies on thermal reactivity of beta-(1,2-allenyl)butenolides and 2-allyl-3-allenylcyclohex-2-enones

A series of thermal pericyclic reactions of beta-allenylfuranones have been studied. It was observed that beta-allenylfuranones would undergo 1,5-hydrogen shift to afford a new type of trienes upon heating. Due to their high reactivity, these trienes would undergo subsequent pericyclic reactions based on the nature of the substituent group R: When R is an alkyl group, the intermediate 4a or 4b would undergo a further 1,7-hydrogen shift to afford a more stable conjugated triene 3; with R being phenyl or cyclopropyl group, the 1,7-hydrogen shift was inhibited and the 4-type conjugated triene would form a six-membered ring 5 via 6 pi-electrocyclization. Interestingly, introducing another C=C double bond into the triene intermediate (R = CH=CH2, the 18-type intermediate would undergo 8 pi-electrocyclization reaction to form an eight-membered ring. Such a transformation was also observed with 2-allyl-3-allenylcyclohex-2-enones. The deuterium-labeling mechanistic studies show that the alkyl groups at the allenyl moiety of 1 participated in the isomerization process via 1,7-hydrogen shifts between 18 A, 20 A, and 29 A.     

Syntheses of 3-substituted 2,3-dihydrobenzofuranes, 1,2-dihydronaphtho(2,1-b)furanes,and 2,3-dihydro-1H-indoles by tandem ring closure-S(RN)1 reactions

3-Substituted 2,3-dihydrobenzofuranes (7a-c), 1,2-dihydronaphtho(2,1-b)furanes (10a-c), and N-substituted 2,3-dihydro-1H-indoles (8a-c, 9a,b) are obtained in very good yields by S(RN)1 photostimulated reactions in liquid ammonia from adequate haloaromatic compounds ortho-substituted with a suitable double bond (3a,b; 4a,b; 5a; 6a,b) and Me3Sn-, Ph2P-, and -CH2NO2 anions. The novelty of the work involves the versatile application of a 5-exo ring closure process during the propagation cycle of the S(RN)1 reaction; the alkyl radical intermediates formed react with the nucleophiles to afford the ring closure-substituted heterocycles. The factors governing the observed product distribution are discussed.     

Nucleophilic addition of grignard reagents to 3-acylindoles: stereoselective synthesis of highly substituted indoline scaffolds

3-Acylindoles undergo nucleophilic-type reactions with Grignard reagents to efficiently afford either cis- or trans-substituted indolines, depending on the different quenching procedures. The enolate intermediate could be trapped by aryl acyl chlorides to provide indolines bearing a quaternary carbon center with high stereoselectivity. In contrast, the use of benzyl bromide as an electrophile results in the fragmentation of the indole ring. The indoline products could be easily transformed into indoles through oxidation with DDQ in a one-pot manner.     

Synthesis of Some New Pyrazole,Pyrimidine, Pyridazine,and Their Fused Derivatives from 3‐Oxo‐3,N‐diphenylpropionamide

The title compounds were obtained from the reactions of 3‐oxo‐3,N‐diphenylpropionamide 3 with dimethylformamide dimethylacetal followed by hydrazine to afford the pyrazole 7 , condensation with benzaldehyde followed by cyclocondensation with guanidine to afford the pyrimidine derivative 13 , condensation with active methylenes followed by azo coupling of the products followed by cyclization to afford the pyridazines 17a , 17b . The pyridazinone 17b was explored for the synthesis of some novel pyridazine‐fused heterocyclic compounds 19 , 21 , 24a , 24b , 24c , and 26 . All structures were proved via their elemental analyses and spectral data.     

Reaction of ferrocenium ion with secondary phosphines: replacement of cyclopentadienyl ligand rather than its C—H functionalization

Russian Chemical Bulletin - The reactions of ferrocenium salts with secondary phosphines Ph2PH, Cy2PH, and Et2PH proceed as replacement of the cyclopentadienyl ring to afford half-sandwich...     

Palladium-catalysed cascade ring expansion reaction of cyclobutanols that have a propargylic moiety with nucleophiles

Cascade ring rearrangement of four-membered ring systems containing various propargylic components by a palladium catalyst is described. The reactions of cyclobutanols that have a propargylic carbonate moiety with phenols as nucleophiles produce phenoxy-induced cyclopentanones in high yields. The reactions proceed in a regio- and diastereoselective manner to afford the substituted cyclopentanones with high selectivities. Imides also act as nucleophiles to produce the imidyl-induced products. Propargylic bromide successfully reacts with sodium alkoxides to produce the corresponding products in good yields.     

3-Pyrrolidinecarboxylic acid for direct catalytic asymmetric anti-Mannich-type reactions of unmodified ketones

We report the development of direct catalytic, enantioselective, anti-selective Mannich-type reactions between unmodified ketones and alpha-imino esters under mild conditions. The reactions were performed using 5-10 mol % of (R)-3-pyrrolidinecarboxylic or (R)-beta-proline as catalyst in an environmentally benign solvent, 2-PrOH, at room temperature. The anti-Mannich products were obtained in good yields with high diastereo- and enantioselectivities (up to anti/syn >99:1, 99% ee). While (3R,5R)-5-methyl-3-pyrrolidinecarboxylic acid is an excellent catalyst for the anti-Mannich-type reactions of aldehydes, it did not efficiently catalyze the corresponding Mannich-type reactions of ketones; (R)-3-pyrrolidinecarboxylic acid did efficiently catalyze the Mannich-type reactions of ketones. (S)-Proline or (S)-2-pyrrolidinecarboxylic acid has been reported to catalyze the Mannich-type reactions of ketones to afford the syn-products. Thus, the position of the carboxylic acid group on the pyrrolidine ring directs the stereoselection of the catalyzed reaction, providing either syn- or anti-Mannich products.     

A New Synthesis of 3-Chloro Butenolides via Rearrangement of 3,3-Dichloro Beta Lactones

4,4-Dialkyl 3,3-dichloro oxetan-2-ones rearrange under Lewis acid catalysis, accompanied by loss of HC1, to afford 4,5-dialkyl 3-chloro butenolides.

We have recently been investigating the reactions of beta lactones under the influence of Lewis acid catalysis.¹ When the lactone ring oxygen is bonded to a secondary carbon atom, a rearrangement occurs in which the beta lactone 1 expands to a butyrolactone 4 with the concommitant migration of a hydrogen or carbon atom into the lactone ring.² If the oxygen is bonded to a tertiary carbon, an ionization/elimination sequence ensues, producing a β, γ-unsaturated carboxylic acid     

Highly-functionalised difluorinated cyclohexane polyols via the Diels-Alder reaction: regiochemical control via the phenylsulfonyl group

A difluorinated dienophile underwent cycloaddition reactions with a range of furans to afford cycloadducts which could be processed regio- and stereoselectively via episulfonium ions, generated by the reaction between their alkenyl groups and phenylsulfenyl chloride. The oxabicyclic products were oxidised to the phenylsulfonyl level and ring opened via E1(C)B or reductive desulfonative pathways to afford, ultimately, difluorinated cyclohexene or cyclohexane polyols.     

Synthesis of phosphorus containing medium ring heterocycles by sequential Claisen rearrangement and ring closing metathesis

An efficient method for the synthesis of novel medium ring phosphorus containing heterocycles starting from phenol derivatives by ruthenium catalyzed ring closing metathesis is described. This work deals with a sequential aromatic Claisen-rearrangement, coupling of an allyl/vinyl phosphonate, and ring closing metathesis reaction. All of these reactions were carried out at ambient temperature to afford the medium-sized phosphorus heterocycles in excellent yields.     

Thermal rearrangement of indolyl oxime esters to pyridoindoles

Acyl oximes derived from a variety of indolylalkanones underwent a ring closure sequence during FVP to afford 9H-pyrido[2,3-b]indoles. Unlike UV light promoted reactions of oxime esters, the mechanism is almost certainly not mediated by iminyl radicals but probably involves tautomerism, elimination of acetic acid, and a final electrocyclic ring closure.