Microwave‐Assisted Solid‐State Synthesis and Characterization of Thiohydantoin Derivatives

Abstract

A new and efficient solid‐state method for the preparation of thiohydantoins is reported. With this method, twelve thiohydantoin compounds have been synthesized in good to excellent yields (81–92%). In addition, this method has the advantages of high yields, a cleaner reaction, simple methodology, and short reaction times.     

Inclusion Complexation of Carbaryl and β-Cyclodextrin in Solution and in the Solid State

This study was carried out with the aim ofinvestigating the interactions between-cyclodextrin and carbaryl, a carbamatepesticide, and their effect on some physico-chemicalproperties of carbaryl, such as aqueous solubility andlipophilicity. The interactions between carbaryl and-cyclodextrin were thoroughly investigated bothin solution and in the solid state. The effect of-cyclodextrin on the aqueous solubility ofcarbaryl was evaluated by the phase solubility method.The amount of carbaryl dissolved increased linearlywith the addition of -cyclodextrin according toan A_L type plot and without precipitation of thecomplex. The apparent stability constant of thecomplex was 289 ± 21 M^-1, assuming a 1 : 1stoichiometry; this value was confirmed by a methodbased on circular dichroism measurements.Equimolar carbaryl/-cyclodextrin solid systemswere prepared by physical-mixing and freeze-drying,and fully characterised by Differential ScanningCalorimetry, X-ray powder diffractometry and FourierTransform Infra-Red analysis. The results of the solidstate study demonstrated that the freeze-drying methodyields a system with a high degree of amorphisationand yields an inclusion complex.The dissolution profile of the pesticide was affectedby the physico-chemical properties of each solidsystem, the freeze-dried form dissolving more rapidly. However, the physical association of-cyclodextrin and carbaryl enhanced the aqueoussolubility of the insecticide as well.     

Acronycine Analog: New Selective Synthesis of 6‐Methoxy‐3,3‐dimethyl‐3H,7H‐pyrano[2,3‐c]xanthen‐7‐one

A new, convenient, and selective route to the dimethylpyrano[2,3‐c]xanthen‐7‐one, analog of acronycine, via aromatization and dehydrogenation reactions from the corresponding saturated hexahydro intermediate is described.     

Crystal Structure and Solid‐State 13C NMR of Methyl α‐d‐Mannofuranoside

The crystal structure of methyl α‐d‐mannofuranoside was determined by X‐ray crystallography. The C‐1–C‐2, C‐2–C‐3, C‐3–C‐4, C‐4–O and O‐4–C‐1 distances within the furanoside ring are 1.513(2), 1.523(2), 1.516(2), 1.445(2) and 1.422(2) Å, respectively. The hydrogen bonding consists of O–H–O interactions which include the anomeric oxygen but exclude the ring oxygen atom. The two hydroxyls OH‐6 and OH‐2 are H‐bond acceptors and donors with H···O distances of 1.92–1.93 Å, whereas the OH‐3 and OH‐5 are only H‐bond donor [H···O distance of 2.04(2) Å]. Additionally, OH‐6 participates in a weak hydrogen bond to the anomeric oxygen [H···O distance of 2.19(3) Å]. The crystalline methyl α‐d‐mannofuranoside adopts an ³ E ring conformation. The analysis of ¹³C CPMAS NMR chemical shifts for solid methyl α‐d‐mannofuranoside confirm such H‐bonding pattern.     

Iodobenzene Diacetate Mediated Solid‐State Synthesis of Heterocyclyl‐1,3,4‐oxadiazoles

Abstract

A simple and efficient method has been developed for the oxidation of various heterocyclyl acylhydrazones 3 with iodobenzene diacetate (IBD) to heterocyclyl‐1,3,4‐oxadiazoles 4 in solid state. The reaction took place at room temperature within few minutes. The products were isolated by simple aqueous work-up in good yields.     

Novel and Efficient Solid‐State Synthesis of 3‐Alkyl‐6‐Aryl‐s‐triazolo[3,4‐b]‐1,3,4‐thiadiazine Derivatives

A novel and efficient solid‐state synthesis of s‐triazolo[3,4‐b]‐1,3,4‐thiadiazine derivatives has been reported. Twelve 3‐alkyl‐6‐aryl‐s‐triazolo[3,4‐b]‐1,3,4‐thiadiazine derivatives have been synthesized in excellent yields with short reaction time.     

Convenient Synthesis and Reactivity of Ethyl 8‐amino‐6‐methyl‐2,3‐dihydro‐4H‐1‐benzopyran‐2‐carboxylate

Abstract

We report and comprehensively describe the synthesis and reactivity of ethyl 8‐amino‐6‐methyl‐3,4‐dihydro‐2H‐1‐benzopyran‐2‐carboxylate. This peptidomimetic building block provides a constrained template that allows for the introduction of various functionalities in a specific spatial orientation.     

Solid‐State Photodimerization of 1,2‐Bis(5′‐pyrimidyl)ethene

The photodimerization of 1,2‐bis(5′‐pyrimidyl)ethene in the solid state is reported. Photolysis of the crystalline solid formed on self‐assembly of 1,2‐bis(5′‐pyrimidyl)ethene and C‐methylcalix[4]resorcinarene and photolysis of the solid recystallized from dichloromethane yielded cis‐anti‐cis‐1,2,3,4‐tetrakis(5′‐pyrimidyl)cyclobutane as the only product. Single‐crystal X‐ray analysis of each of these solids confirms that the alkenes are π‐stacked, colinear, and separated by less than 4.2 Å.     

Alternative Route for the Synthesis of 6‐Methoxy‐5‐methyl‐α‐tetralone and 6‐Methoxy‐2,5‐dimethyl‐α‐tetralone

The ketoesters 3 and 4, obtained by the condensation of 2‐cyclohexanone carboxylate and 1‐chloro‐3‐pentanone, were heated with 2,3‐dichloro‐5,6‐dicyanobenzoquinone (DDQ) to yield the dienones 5 and 6, which on hydrolysis with potassium t‐butoxide and dimethyl sulfoxide afforded tetralin 8. These were converted to tetralone 10 by methylation and oxidation respectively. Further methylation of 10 yielded tetralone 11.     

Polymerization of Acrylamide in Aqueous Solution of Poly(N‐isopropylacrylamide) at Lower Critical Solution Temperature

Acrylamide (AAm) was found to polymerize in a solution of poly(N‐isopropylacrylamide) (PNIPAAm) in water at around its lower critical solution temperature (LCST) (32°C) without any initiators. This phenomenon was specifically observed in aqueous solutions of the polymers having LCST such as PNIPAAm and poly(methylvinylether) (PMVE). AAm polymerized only when PNIPAAm and AAm were dissolved in water below LCST of PNIPAAm and then the solution was warmed up to the polymerization temperature (40°C). On the other hand, the polymerization of AAm did not proceed when AAm was added into aqueous PNIPAAm solution during and after the phase separation above 32°C. Furthermore the polymerizability of AAm was remarkably affected by the concentration and molecular weight of the PNIPAAm additives. Under the condition of lower PNIPAAm concentration (0.30 mol/L), the increase in the molecular weight of PNIPAAm considerably increased the molecular weight of the resulting PAAm but decreased the yield of PAAm. Under the condition of higher PNIPAAm concentration (0.60 mol/L) the polymerizability was not so affected by the molecular weight of PNIPAAm, while the molecular weight of PAAm formed by using higher molecular weight PNIPAAm was higher than those of PAAm formed by using lower molecular weight PNIPAAm. Moreover, the molecular weight of PAAm formed by the PNIPAAm induced polymerization of AAm was much higher than that of the polymer obtained by the radical polymerization using AIBN in THF or VA‐ 061 in water.     

Pseudorotaxanes of β-Cyclodextrin with Diamino End-functionalized Oligo-phenyl and -benzyl Compounds in Solution and in the Solid State

-Cyclodextrin forms a 1:1 host:guest inclusion complex ([2]pseudorotaxane) with 4-[2-(4-aminophenyl)ethyl]-benzenamine (1) in water as determined by 1D and 2D NMRexperiments. In the crystalline state, the structure of the complex has revealed a 2:2 stoichiometry, with two CD molecules forming head-to-head dimers byH-bonds between the secondary O3 hydroxyl groups and enclosing two molecules of the guest. The packing mode of the present complex is encountered for the first time, since it does not belong to any of the four known packing types of the dimeric CD inclusion complexes. On the other hand,N ¹,N ⁴-bis(4-aminophenyl)-1,4-benzenedimethanamine 2), which is longer than 1 by a phenylene diamine unit, has not afforded any crystals, at present, however it threads into CD in aqueous solution forming most probably [2]- and [3]pseudorotaxanes. The solution structures and the equilibria in this system are investigated.     

Facile Synthesis of 2‐Alkylthio‐5,5‐dimethyl‐4H‐imidazol‐4‐ones

The isothiocyanate 3, obtained from aza‐Wittig reaction of iminophosphorane 2 with CS₂, reacts with phenylhydrazine to give thiosemicarbazide 4. Reactions of 4 with alkyl halides in the presence of K₂CO₃ directly provided 2‐alkylthio‐4H‐imidazol‐4‐ones 6 in good yields.     

Conformational Heterogeneity of a Tripeptide in the Solid State and in Solution: Characterization of a γ-Turn Containing Incipient Hairpin in Solution

A terminally blocked tripeptide Boc--Ala-Aib--Ala-OMe 1 with noncoded amino acids forms a novel type of hairpin structure containing a -turn instead of a conventional -turn in the central loop region in solution. This new type structural motif was characterized by NMR and restraint molecular dynamics simulation study. In the solid state peptide 1 adopts an extended backbone conformation and self-assembles to form supramolecular -sheet.     

Kinetic Study of Radical Polymerization VIII. A Comprehensive Study of Solution Copolymerization of Vinyl Acetate and Methyl Acrylate by 1H‐NMR Spectroscopy

Radical copolymerization reaction of vinyl acetate (VA) and methyl acrylate (MA) was performed in a solution of benzene‐d₆ using benzoyl peroxide (BPO) as the initiator at 60°C. Kinetic studies of this copolymerization reaction were investigated by on‐line ¹H‐NMR spectroscopy. Individual monomer conversions vs. reaction time, which was followed by this technique, were used to calculate the overall monomer conversion, as well as the monomer mixture and the copolymer compositions as a function of time. Monomer reactivity ratios were calculated by various linear and nonlinear terminal models and also by simplified penultimate model with r _2(VA)=0 at low and medium/high conversions. Overall rate coefficient of copolymerization was calculated from the overall monomer conversion vs. time data and k _p  . k _t ^?0.5 was then estimated. It was observed that k _p  . k _t ^?0.5 increases with increasing the mole fraction of MA in the initial feed, indicating the increase in the polymerization rate with increasing MA concentration in the initial monomer mixture. The effect of mole fraction of MA in the initial monomer mixture on the drifts in the monomer mixture and copolymer compositions with reaction progress was also evaluated experimentally and theoretically.     

γ-Radiation-Initiated Polymerization of Acrylonitrile in Aqueous Solution and in Emulsion

The γ-radiation-initiated polymerization of acrylonitrile (AN) at 25[ddot] C has been studied, both in aqueous solution and in emulsion, at dose rates between 70 and 175 krad/hr. The effect of added emulsifier, sodium lauryl sulfate (SLS), on reaction rates, R_p, and on polymer molecular weight, M_n, has been investigated. G (monomer polymerized) values ranged from 7,500 in aqueous solution to 20,000 in bulk to 45,000 in emulsion, all based on the total energy absorbed. In the aqueous solution polymerization, where R_p is approximately first order in initial monomer concentration over the range 0.15 ± [AN]_o ± 1.06 moles/liter, addition of SLS increases R_p but does not influence the order of the reaction with respect to [AN]_o. In the emulsion system at 70 krad/hr and at a phase volume ratio AN/H₂O of 1/2, (PR = 1/2), R_p varies as [SLS]^0.1 over the concentration range 0.01 ± [SLS] ± 2.5± wt/vol of aqueous phase. At the same PR value, and at 80 krad/hr, M_n of the polymer (measured by viscometry in dimethylformamide solution) is effectively independent of [SLS] in the range of 0.01 ± [SLS] ± 10± wt/vol of aqueous phase. Initial R_p values are either independent of PR in the range 1/3 ± PR ± 1/1 or exhibit an insensitive and unsystematic dependence thereon. Based on measurements at 70 and at 175 krad/hr, the intensity exponent of R_p at PR = 1/2 is approximately 0.4.     

Solution properties and mesophase formation of 4‐phenyl‐benzoylcellulose

Cellulose samples were derivatized in dimethylacetamide/LiCl (DMAc/LiCl) to give 4phenylbenzoylcelluloses (PBCs). The process is quantitative and leads to an highly substituted product, as verified by elemental analysis, IR and ¹³CNMR spectroscopy. PBC samples were characterized by viscometric and light scattering measurements in DMAc. The persistance length q is used to evaluate the theoretical critical volume fraction for mesophase formation (v _th, which has been found higher than the experimental critical one (v _exp)     

Facile Synthesis and Unusual Methanesulfonylation Reaction of (2R,3R)‐1,4‐Dimethoxy‐1,1,4,4‐tetrasubstituted‐2,3‐butanediols

A facile method for the synthesis of (2R,3R)‐1,4‐dimethoxy‐1,1,4,4‐tetrasubstituted‐2,3‐butanediols involving oxidative cleavage of benzylidene acetal as a key step is described. These sterically hindered diols unusually formed cyclic sulfites as the major product under methanesulfonylation reaction conditions.     

Thermolysis and [3+2]‐Cycloaddition Reactions of 2,3‐Diferrocenyl‐ and 2,3,‐Diruthenocenylcyclopropenones

Abstract

2,3‐Diferrocenyl‐ and 2,3‐diruthenocenylcyclopropenone undergo thermolysis at ～180°C with opening of the small ring via ketenocarbenes. Intramolecular transformation of the latter occurs with elimination of CO to yield dimetallocenylacetylenes. Alternatively, they enter into 1,3‐dipolar cycloaddition reactions with C≡C or C?C multiple bonds to give cyclopentadienone or cyclopentenone derivatives, respectively.     

Solid State NMR and Fluorescence Studies of Conjugated Polymer Nanocomposties

^13C spin-lattice relaxation times （T1） of a conjugated polymer MEH-PPV in polymer/ layered silicate nanocomposites together with the steady state fluorescence emission and transient fluorescence decay measurements have been investigated. The T1 values of the conjugated carbons decrease dramatically according to the reduction of polymer concentration in the nano composites, while the fluorescence life times （τ） show a linear prolonging tendency. The results are explained from the point of view of molecular dynamics.