Sequential isomerization and ring-closing metathesis: masked styryl and vinyloxyaryl groups for the synthesis of benzo-fused heterocycles

The use of an aryl allyl ether and an arylallyl group as masked vinyl ether and 1-propenylphenyl groups for ring-closing metathesis (RCM) leading to the synthesis of benzo-fused heterocycles was demonstrated by using a ruthenium-mediated isomerization followed by a ruthenium-mediated RCM reaction. This resulted in the syntheses of a variety of products including two substituted benzo[1,4]dioxins, a naphtho[2,3-b][1,4]dioxin, a 2H-chromene and a benzo[b]furan.     

Cu(II)-catalyzed one-pot synthesis of fully substituted dihydrothiophenes and thiophenes from thioamides and enynones

A facile and direct synthetic method was developed for the construction of fully substituted dihydrothiophenes, which via a copper-catalyzed Michael addition/intramolecular cyclization/protonation cascade reaction of readily available thioamides with enynones under air atmosphere. This approach provides 2,3-dihydrothiophenes with up to 92% yield in a one-pot process. In addition, several fully substituted thiophenes could also be synthesized by changing the substituents of thioamides.     

Synthesis and properties of thermoplastic propyl-etherified amylose

Amylose was etherified with 1-bromopropane in DMSO. The degree of substitution (DS) was varied by altering the feed ratio of 1-bromopropane. The structures of the products were characterized by IR and 1H-NMR spectroscopy. When the molar feed ratio of 1-bromopropane to hydroxyl groups of amylose was beyond 7.5, the hydroxyl groups were completely substituted with propyl ether groups. The etherified amylose with DS 1.9 showed a glass transition temperature (T_g), and that with DS 2.3 or 3.0 showed both T_g and melting temperature (T_m) (DS 3.0 means complete substitution). The etherification imparted melt processability and solubility in nonpolar organic solvent to amylose.     

Synthesis of methyl substituted [5,6]- and [7,8]-fused pyridocoumarins via the iodine-catalyzed reaction of aminocoumarins with n-butyl vinyl ether

2-Methyl substituted [5,6]- or [7,8]-fused pyridocoumarins are prepared from the Povarov-type, three-component reactions of 6- or 7-aminocoumarins with n-butyl vinyl ether, catalyzed by iodine in refluxing acetonitrile, through the aza-Diels–Alder reaction of the initially formed N-iminoaminocoumarins with a second equivalent of the vinyl ether.     

Synthesis of (E)-4-ethoxyphenyliminomethylaryls and their hydrochlorides

Condensation of p-phenetidine with the substituted aromatic benzaldehydes in methanol results in (E)-4-methylethoxyphenyliminoaryl derivatives. The latter react with gaseous hydrogen chloride in diethyl ether to form 4-ethoxymethylphenyliminoaryl hydrochlorides.     

Expanding the substitution pattern of 2(1H)-pyrazinones via Suzuki and Heck reactions

Various 3,5-dichloropyrazinones were substituted at the C-3 position with (hetero)aryl, alkyl and alkenyl groups by means of Suzuki and Heck reactions. The methodology could be extended to reactions on the far less reactive C-5 position by transhalogenation of the 5-Cl substituent to a 5-Br or a 5-I group prior to performing the cross-coupling.     

Synthesis and reactions of 1,10-phenanthroline-2(1H)-thione: a facile synthesis of 2,2′-thiobis-1,10-phenanthroline

Treatment of 2-chloro-1,10-phenanthroline with NaSH hydrate in DMF, Na₂S nonahydrate in DMF or thiourea in refluxing ethanol readily afforded 1,10-phenanthroline-2(1H)-thione. This thione undergoes reaction with 1,2-dibromoethane to yield a thiazole bromide salt. Upon heating the thione in diphenyl ether with 2-chloro-1,10-phenanthroline, the hydrochloride salt of 2,2′-thiobis-1,10-phenanthroline precipitated and could be converted into the corresponding free base on treatment with aqueous base. Heteroaryl substituted sulfides could be prepared by treatment of 2-chloro-1,10-phenanthroline with pyridine-2-thione or pyrimidine-1-thione with potassium carbonate in DMF.     

One-pot three-component reaction of fluoroalkanesulfonyl azide, vinyl ether and aldehyde: the formation of polysubstituted fluorinated oxazolidines

Efficient and diastereoselective synthesis of highly substituted fluorinated oxazolidines was achieved via a one-pot three-component reaction of fluoroalkanesulfonyl azides 1, vinyl ether 2 and various aldehydes at 0 °C within 10 min in moderate to good diastereoselectivities (syn/anti). A competing process could be involved in the initial step and an unstable fluorinated aziridine was postulated as the intermediate for these reactions. Additionally, rational transition states were also proposed to elucidate the diastereoselectivities. This synthetic method provides a convenient and expeditious access to N-per(poly)fluoroalkanesulfonyl oxazolidines.     

Novel crown ethers with pendant,proton-ionizable,chromogenic groups

Synthesis of fifteen new chromogenic crown ethers is described in which one phenyl group of diphenylamine has been substituted at the 2-, 4-, and 6-positions with strongly electron-withdrawing groups and the other phenyl group bears an oxymethyl crown ether substituent. Structural variations include the crown ether ring size, identity of the electron-withdrawing groups, acidity of the amine function, and positioning of the oxymethyl crown ether substituent ortho, meta, and para to the amine nitrogen. Preparation of a structurally-related chromogenic bis(crown ether) is also reported.     

Direct N- and C-alkenylation of nitrogen-containing heterocycles with magnesium alkylidene carbenoids

Treatment of magnesium alkylidene carbenoids, which were generated from 1-chlorovinyl p-tolyl sulfoxides with isopropylmagnesium chloride at −78 °C in toluene, with N-lithio nitrogen-containing heterocycles gave N-alkenylated products in moderate to good yields. Also, the reaction of C-lithio indoles, which were generated from N-protected indoles, with magnesium alkylidene carbenoids gave C-2 or C-3 alkenylated products, corresponding to the protective group. The intermediate of these reactions were found to be the alkenyl anion, which could be trapped with electrophiles to give the heterocycles having fully substituted alkenes.     

Synthesis and characterization of novel heat resistant poly(amide imide)s

A series of new poly(amide imide)s was prepared from new diacid containing sulfone, ether, amide and imide groups with various aromatic diamines. The diacid was synthesized via four steps, starting from reaction of 4-aminophenol with 4-nitrobenzoyl chloride in the presence of propylene oxide afforded N-(4-hydroxy phenyl)-4-nitrobenzamide. In the second step, reduction of nitro group resulted in preparation of 4-amino-N-(4-hydroxy phenyl) benzamide. In the next step for the preparation of diamine, the reaction of 4-amino-N-(4-hydroxy phenyl) benzamide with bis-(4-chlorophenyl) sulfone in the presence of K₂CO₃ was achieved. The prepared sulfone ether amide diamine was reacted with two moles of trimellitic anhydride to synthesize related sulfone ether amide imide diacid. The precursors and final monomer were characterized by FT-IR, H-NMR and elemental analysis. Direct polycondensation reaction of the sulfone ether amide imide diacid with different diamines in the presence of triphenyl phosphite afforded five different poly (sulfone ether amide imide amide)s. The obtained polymers were fully characterized and their physical properties including thermal behavior, thermal stability, solubility, and inherent viscosity were studied.     

Diels-Alder reaction of 4-halogenated masked o-benzoquinones with electron-rich dienophiles

Inverse-electron-demand Diels-Alder reaction of masked o-benzoquinones (MOBs) ensuing from the corresponding 4-halo-2-methoxyphenols with styrene, dihydrofuran and ethyl vinyl ether, butyl vinyl ether, phenyl vinyl sulfide and vinyl acetate to afford the highly functionalized halogen substituted bicylclo[2.2.2]octenones are described.     

Regioselective ring opening of unsymmetrical cyclic ethers with the A1C13-NaI-acetonitrile system: Application to hydroxylation of ent-kaurene.

Unsymmetrically substituted 5-membered cyclic ethers were effectively cleaved with the A1C1₃-NaI-CH₃CN system at the less hindered carbon atom to afford δ-iodoalcohols. Conversion of ent-kaurene to ent-14α- and ent-12β-hydroxykaurene was achieved through the ring opening of the cyclic ether with the present system as a key step.     

氟取代聚芳醚酮低温合成及其结构研究

通过傅克酰基化反应合成4,4'-二(4-氟苯甲酰基)二苯醚、4,4'-二(五氟苯甲酰基)二苯醚、4,4'-二(4-氟苯甲酰基)二苯硫醚以及4,4'-二(五氟苯甲酰基)二苯醚4种长链双卤单体,并进一步制备了含二氮杂萘酮聚芳醚酮聚合物.通过多氟取代双卤单体在含二氮杂萘酮聚芳醚酮聚合物主链中引入氟原子.多氟取代双卤单体具有多...     

Catalyst free 1,3-dipolar cycloaddition of 3-oxo-1,2-pyrazolidinium ylides to β-trifluoroacetyl vinyl ethyl ether: Synthesis of 6-trifluoroacetyl substituted bicyclic pyrazolidinones

A catalyst free cycloaddition reaction of 3-oxo-1,2-pyrazolidinium ylides with β-trifluoroacetyl vinyl ethyl ether is reported, which proceeded smoothly at ambient temperature and afford the bicyclic pyrazolidinone products in good yield. This is the first report of synthesis of 6-trifluoroacetyl substituted bicyclic pyrazolidinones that are potentially anti-microbial and herbicidal.     

Model compounds of caged capsaicin: design, synthesis, and photoreactivity

Molecules were prepared with substituted nitrobenzyl groups covalently bonded to N-(4-hydroxy-3-methoxybenzyl)acetamide (2) by ether or carbonate linkages. These compounds decomposed under irradiation at 363 nm. Those with carbonate linkages decomposed at slower rates than those with ether linkages. Molecules with dimethoxy-substituted benzyl groups decomposed more slowly than monomethoxy-substituted benzyl groups due to the electronic characteristics of the benzylic carbon.     

Regioselective synthesis of 1,3,5- and 1,3,4,5-substituted pyrazoles via acylation of N-Boc-N-substituted hydrazones

Acylation of N-Boc-N-methylhydrazones followed by TFA treatment affords regioselective access to substituted pyrazoles. Both regioisomers of 1-methyl-3,5-disubstituted-1H-pyrazoles can be selectively obtained. This procedure can also be employed for the regioselective preparation of fully substituted 1H-pyrazoles.     

A two-step procedure for the preparation of mono-protected bis-N-heterocyclic alkyl ether systems

A two-step convenient sequence for the synthesis of previously inaccessible mono-Boc-protected bis-N-heterocyclic alkyl substituted ether derivatives 4 is described. Mitsunobu protocol was applied to the preparation of pyridinyl ether precursor 5. The reduction of the electron rich pyridinyl system 5 has been achieved catalytically using the combination of PtO₂-H₂SO₄ or PtO₂-pTsOH under a hydrogen atmosphere maintained by a gas balloon at ambient temperature.     

A one-pot synthetic approach to the functionalized isomeric ellipticine derivatives through an imino Diels-Alder reaction

An efficient, three component, one-pot synthesis of new isomeric ellipticine derivatives prepared through an imino Diels-Alder reaction of 3-aminocarbazoles and substituted benzaldehydes with electron-rich alkenes such as 3,4-dihydro-2H-pyran, 2,3- dihydrofuran and ethyl vinyl ether catalyzed by InCl₃ (10 mol %) in ionic liquid is reported. In the case of substituted benzaldehydes, reductive amination is observed.