RAFT Polymerization of Styrene in the Presence of 2‐Nonyl‐benzoimidazole‐1‐carbodithioic Acid Benzyl Ester

A novel dithiocarbamate, 2‐nonyl‐benzoimidazole‐1‐carbodithioic acid benzyl ester ( 1a ), was synthesized and successfully used in RAFT polymerization of styrene in bulk with thermal initiation. The effect of molar ratio of styrene to RAFT agent on the polymerization was investigated. The linear relationship between ln([M]₀/[M]) and polymerization time indicated that the polymerization was first‐order with respect to monomer concentration. The molecular weights increased linearly with monomer conversion and were close to corresponding theoretical values. The molecular weight distributions (M _w /M _n ) kept very narrow (M _w /M _n <1.1) at a wide range of conversions of 14.2% to 73.3%. The obtained polymer had a strong ultraviolet absorption at 329 nm, which indicated that the 1a moiety remained at the end of polymer chain.     

2‐Hydroxy‐1,2,3,6‐tetrahydro‐azulen‐6‐carboxylic Acid Ethyl Ester—A Novel Precursor for a New Class of Liquid Crystalline Materials

A novel approach for the syntheses of carbene adduct 4 is reported. A ring-enlargement strategy was employed for the synthesis of precursors 5 and 6 and established the mechanism of the formation of azulene derivative 6. Synthesis of target precursor 13, a novel precursor for the synthesis of new mesogenic materials, and its various halogenated derivatives (14–16) was carried out.     

Organic Base‐Catalyzed Stereoselective Isomerizations of 4‐Hydroxy‐4‐phenyl‐but‐2‐ynoic Acid Methyl Ester to (E)‐ and (Z)‐4‐Oxo‐4‐phenyl‐but‐2‐enoic Acid Methyl Esters

We have developed a 1,4‐diazabicyclo[2.2.2]octane (DABCO)‐catalyzed isomerization of 4‐hydroxy‐4‐phenyl‐but‐2‐ynoic acid methyl ester to (E)‐4‐oxo‐4‐phenyl‐but‐2‐enoic acid methyl ester and an N,N‐diisopropylethylamine‐catalyzed isomerization of the same substrate to (Z)‐4‐oxo‐4‐phenyl‐but‐2‐enoic acid methyl ester.     

Nitroimidazoles,Part 1. An Unexpected Reactivity During the Cyclization of 3‐(4‐Amino‐1‐benzyl‐2‐ethyl‐1H‐imidazol‐5‐ylsulphanyl)‐propionic Acid Methyl Ester

Nucleophilic substitution of the 5‐bromo group in 1 by methyl 3‐mercaptopropionate gave the 5‐alkyl‐mercapto derivative 2. Reduction of 2 with H₂/Pd led to the amine 3, meanwhile reduction with Fe/HOAc afforded the 5‐acetamido derivative 4 and not the cyclized derivative 1,3,8‐triaza‐azulen‐7‐one 6, as expected. Treatment of 3 with NaOMe/MeOH furnished the racemic mixture 5a and 5b via an unexpected reactivity.     

Unexpected Isolation of 4‐Isothiocyanatomethylene‐4H‐pyridine‐1‐carboxylic Acid Ethyl Ester as Potential Template in Organic Synthesis

The synthesis of 4‐isothiocyanatomethyl‐pyridine 4 in 36% yield by Hasegawa and Kotani (Japanese patent 49088878, 1974) has spurred us to investigate this preparation in detail. In addition to this compound, 4‐isothiocyanatomethylene‐4H‐pyridine‐1‐carboxylic acid ethyl ester 3 can be isolated. The synthesis of both compounds 3 and 4 were optimized to 75% and 50% yield respectively. Reaction of compound 3 with methylamine gave thiourea derivatives 5, the same product obtained on reacting 4‐isothiocyanatomethyl‐pyridine 4 with methylamine. We succeed in adjusting the reaction conditions to obtain high yield either from compound 3 or isothiocyanate derivatives 4.     

One‐Pot Synthesis of 2‐Arylthio‐2‐cyclohexenone Derivatives by the Diels–Alder Reaction of 4‐Arylthio‐3‐hydroxy‐2‐pyrones

The base‐catalyzed Diels–Alder reactions of 4‐arylthio‐3‐hydroxy‐2‐pyrones are reported. Treatment of 4‐arylthio‐3‐hydroxy‐2‐pyrones and dienophiles with triethylamine gave 2‐arylthio‐2‐cyclohexenone derivatives by the Diels–Alder reaction involving a decarboxylation in excellent to reasonable yields.     

Synthesis of Acylated Methyl 2‐Acetamido‐2‐Deoxy‐α‐D‐Mannopyranosides

Abstract

2‐Acetamido‐2‐deoxy‐β‐D‐mannopyranose (1) was glycosylated by the Fischer method using an acidic ion‐exchange resin as the catalyst to give α‐methyl glycoside 2. Selective pivaloylations of methyl 2‐acetamido‐2‐deoxy‐α‐D‐mannopyranoside (2) have been studied under various reaction conditions. Two partially pivaloylated products were submitted to additional acetylations. All structures were established by NMR spectroscopy. Structure of the methyl 2‐acetamido‐2‐deoxy‐3,6‐di‐O‐pivaloyl‐α‐D‐mannopyranoside (4) was determined by X‐ray analysis.     

Synthesis of Substituted 2‐Amino‐cyclobutanones

A series of weakly nucleophilic nitrogen derivatives including carbamates, amides, sulfonamides, and anilines were reacted with 1,2‐bis(trimethylsilyloxy)cyclobutene under acidic conditions to afford various substituted 2‐aminocyclobutanone derivatives 3a–i in modest to excellent yields.     

Convenient Method for Synthesis of Substituted 2‐Amino‐2‐chromenes

Some substituted 2‐amino‐2‐chromenes were synthesized by the reaction of arylidenemalononitriles with 1‐naphthol or 2‐naphthol in the presence of sodium hydroxide as catalyst under solvent‐free condition.     

An Efficient Synthesis of Derivatives of 2‐Acetamido‐4‐amino‐2,4,6‐trideoxy‐D‐galactopyranose

Abstract

Methyl 2‐acetamido‐4‐amino‐2,4,6‐trideoxy‐α‐D‐galactopyranoside (10) was synthesized from D‐glucosamine hydrochloride in eight steps in an overall yield of 31%. Key steps include the selective benzoylation at O‐3 of methyl 2‐acetamido‐2,6‐dideoxy‐α‐D‐glucopyranoside in 89% yield and the subsequent Mitsunobu reaction using diphenylphosphoryl azide as the azide source which proceeded in 92% yield. Di‐ and mono‐benzyloxycarbonyl derivatives of 10 were also prepared.     

Novel Copolymers of N‐(4‐Bromophenyl)‐2‐Methacrylamide with 2‐Acrylamido‐2‐Methyl‐1‐Propanesulfonic Acid

The new acrylamide monomer, N‐(4‐Bromophenyl)‐2‐methacrylamide (BrPMAAm) has been synthesized by reacting 4‐Bromoaniline with methacryloyl chloride in the presence of triethylamine(NR₃) at 0–5°C. The radical‐initiated copolymerization of (BrPMAAm), with 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPS) has been carried out in dimethylformamide (DMF) solution at 70±1°C using 2,2′‐azobisisobutyronitrile (AIBN) as an initiator with different monomer‐to‐monomer ratios in the feed. The copolymers were characterized by FTIR, ¹H‐ and ¹³C‐NMR spectroscopy. The copolymer composition was evaluated by nitrogen content (N for AMPS‐units) in polymers led to the determination of reactivity ratios. The monomer reactivity ratios for BrPMAAm (M₁)‐AMPS (M₂) pair were computed using the Fineman‐Ross (F‐R), Kelen‐Tüdös (KT) and Extended Kelen‐Tüdös (EKT) methods. These parameters were also estimated using a non‐linear computational fitting procedure, known as reactivity ratios error in variable model (RREVM). The mean sequence lengths determination indicated that the copolymer was statistically in nature. By TGA and DSC analyses, the thermal properties of the polymers have been studied. The antimicrobial effects of polymers were also tested on various bacteria, and yeast.     

A Novel Chemo‐selective Epoxidation across Acrylate Ester: Synthesis of New Water‐Soluble Forskolin Analogues

While removing the TBDMS group from OH protection, a novel epoxidation reaction occurred across acrylate ester attached to a forskolin fragment. Besides spectroscopic data, the epoxide formation was confirmed by ring opening with a secondary amine. This unique epoxidation reaction, to our knowledge, is not known in the literature. This reaction led us to discover a simple deblocking protocol. The epoxide and the desired Michael substrates were used to introduce imidazole into forskolin.     

Bromination Products of 2‐Substituted 5,7‐Dimethoxy‐4‐Naphthols

Bromination in acetic acid is favored at C‐8 in 5,7‐dimethoxy‐4‐naphthol when the C‐2 substituent is methyl carboxylate, whereas C‐1 is favored when the C‐2 substituent is either acetoxymethylene or methyl.     

Efficient Synthesis of 2‐(N‐Substituted)‐2‐imidazolines and 2‐(N‐Substituted)‐1,4,5,6‐tetrahydropyrimidines

A general method for the preparation of 2‐(N‐Substituted)‐2‐imidazolines and 2‐(N‐Substituted)‐1,4,5,6‐tetrahydropyrimidines is described. These heterocycles can be synthesized from their respective anilines with 2‐chloro‐2‐imidazoline or 2‐chloro‐1,4,5,6‐tetrahydropyrimidine, generated in situ from imidazolidin‐2‐one and tetrahydropyrimidin‐2(1H)‐one activated by dimethyl chlorophosphate, in good to excellent yields.     

Structure of 2,4,4,5,5‐pentamethyl‐2‐imidazoline‐1‐oxyl‐3‐oxide

The crystal and molecular structures of the stable nitroxide radical 2,4,4,5,5pentamethyl2imidazoline1oxyl3oxide was determined. The N—O bond lengths are 1.279(2) and 1.280(2), respectively. The O^-—N⁺=C—N— O fragment is nearly planar with carbon atoms of the ethyl fragment that deviated from the O—N⁺=C—N—O plane by –0.204(5) and +0.176(5). The minimum intermolecular distance between the oxygen atoms of NO groups is 4.094.     

Efficient Synthesis of Substituted 2‐Amino‐3‐carbethoxythiophenes

A microwave‐assisted method for the synthesis of a variety of thiophene o‐aminoesters (2a–l) has been developed, starting from an appropriate aldehyde, methyl ketone or acetoacetate ester with ethyl cyanoacetate in the presence of elemental sulfur.     

Novel Synthetic Route of (2S)‐6‐Fluoro‐4‐oxo‐3,4‐dihydro‐2H‐chromene‐2‐carboxylic Acid

(2S)‐6‐Fluoro‐4‐oxo‐3,4‐dihydro‐2H‐chromene‐2‐carboxylic acid, a key intermediate of Fidarestat, was synthesized from natural chiral pool D‐mannitol. Its structure was confirmed by optical analyses, elemental analyses, and IR, ¹H NMR, and ESI‐MS spectra.     

Microwave‐Promoted Ullmann Condensation of 2‐Aminopyridines with 2‐Chlorobenzoic Acids

A new efficient synthetic method of microwave‐promoted Ullmann condensation of 2‐aminopyridines with 2‐chlorobenzoic acids to yield various substituted 11H‐pyrido[2,1‐b]quinazolin‐11‐ones in dry media is presented. Results were compared with those obtained following the classical heating.     

Convenient Synthesis of Some Substituted 5‐Oxonitriles under Aqueous Conditions: Synthesis of 3,4‐Dihydro‐2H‐pyrrole‐2‐carbonitriles

Michael additions of [(diphenylmethylene)amino]acetonitrile (1) to α,β‐unsaturated ketones (chalkones) (2) under aqueous conditions allow for the highly diastereoselective synthesis of substituted 2‐amino‐5‐oxonitriles (3). Selective removal of diphenylmethylene protecting group, followed by in situ cyclization, gives 3,5‐diaryl‐3,4‐dihydro‐2H‐pyrrole‐2‐carbonitriles (4).