Bromination of 4‐Dichloromethyl‐4‐methylcyclohexa‐2,5‐dien‐1‐ones

Bromination of 4‐dichloromethyl‐4‐methylcyclohexa‐2,5‐dien‐1‐one and 4‐dichloromethyl‐3,4‐dimethylcyclohexa‐2,5‐dien‐1‐one has been studied. The reaction conditions required for the formation of mono‐, di‐, and tribrominated products have been optimized.     

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.     

Synthesis and study of 4‐(4′‐n‐alkoxybenzoyloxybenzoyl)‐4′′‐n‐butoxyanilides

Thirteen compounds with ester and amide linkages were synthesized and their mesogenic properties evaluated. Methyl to n‐propyl derivatives exhibit nematic phases, n‐butyl to n‐decyl derivatives exhibit smectic and nematic mesophases, whereas n‐dodecyl to n‐octadecyl derivatives exhibit only smectic phases. All the smectic homologues exhibit smectic C phases. Middle members of the homologous series exhibit polymorphism of smectic mesophase. A plot of transition temperatures versus number of carbon atoms in the alkoxy chain reveals an odd–even effect for nematic–isotropic transition temperatures. Nematic–isotropic and smectic–cholesteric thermal stabilities of the prepared compounds (series I) are higher compared to those of previously reported compounds, series A, B and C. The results indicate that a simple reversal of a central linkage has a dramatic effect on the appearance of smectic mesophase in a homologous series. The structures of the synthesized compounds were characterized using elemental analysis, thin‐layer chromatography and spectral data.     

Synthesis of 4‐Substituted‐ and 1,4‐Disubstituted‐4‐Hydroxypyrrolidin‐2‐ones

This report describes the synthesis of 4‐substituted‐ and 1,4‐disubstituted‐4‐hydroxypyrrolidin‐2‐ones by cyclization of intermediate γ‐aminoesters prepared from alkylbenzylamines, α‐bromoketones, and lithio ethyl acetate.     

Synthesis of 1,1‐Dimethyl‐4‐indanol Derivatives

The synthesis of 1,1‐dimethyl‐4‐indanols (3a,b) has been achieved by intramolecular Friedel–Crafts cyclization of 2‐(3‐methyl‐2‐butenyl)phenols (5a,b) or 1‐methoxy‐2‐(3‐methyl‐2‐butenyl)benzenes (6a,b) followed by demethylation, respectively.It was found that the solvent was critical for the formation of different products in the intramolecular Friedel–Crafts reactions of 6. The unexpected product 4‐methoxy‐1,1,6,6‐tetramethyl‐as‐hydrindacene (11) was obtained from the Friedel–Crafts reactions of 6a, and its structure was confirmed by X‐ray diffraction analysis. The key intermediates 5a,b were prepared by ortho‐alkenylation of phenols with 1‐bromo‐3‐methyl‐2‐butene, and the reaction temperature exerted an obvious impact on the yield of 2‐(3‐methyl‐2‐butenyl)phenol (5a).     

Facile Synthesis of 2‐Alkylthio‐3‐alkyl‐5‐phenylmethylidene‐4H‐imidazol‐4‐ones

2‐Alkylthio‐3‐alkyl‐5‐phenylmethylidene‐4H‐imidazol‐4‐ones 6 were synthesized by N‐alkylation and S‐alkylation of 2‐thioxo‐5‐phenylmethylidene‐4‐imidazolidinone 5, which was obtained via cyclization of vinyl isothiocyanate 4 with excess ammonium hydroxide (28% NH₃ in water).     

Synthesis of cis‐3‐methyl‐4‐aminopiperidine Derivatives

A facile approach for the preparation of cis‐3‐methyl‐4‐aminopiperidine derivatives is described. The synthesis was carried out via regioselective ring opening of N‐benzyl‐3‐methyl‐3,4‐epoxi‐piperidine (8), which can be easily obtained in two steps from the corresponding N‐benzyl‐pyridinium salt (5). Seven new cis‐3‐methyl‐4‐amino and amido piperidines compounds were obtained.     

Crystal structure of 1,2‐[4‐butoxybenzoyloxy‐4′‐pentyl]diphenylethane

The crystal structure of 1,2‐[4‐butoxybenzoyloxy‐4′‐pentyl]diphenylethane (C₃₀H₃₆O₃) has been determined by direct methods using single crystal X‐ray diffraction data. It crystallizes in the monoclinic system with space group P2₁/a and Z?=?4. The unit cell parameters are: a?=?8.098(1), b?=?10.926(1), c?=?29.643(2)?Å and β?=?94.01(1)°. The final reliability factor is R?=?0.073 and the goodness of fit is equal to 1.027. The molecular arrangement is very typical, with molecules associated in dimers very closely parallel to the Oz axis. In a given dimer, the backbones of the two molecules run alongside each other; this association can be attributed to strong dipole–dipole interactions through the polar ester and ether groups. In addition these dimers are connected to neighbours via dipole–dipole interactions along the Oy direction. There are numerous very weak van der Waals interactions, particularly between the terminal aliphatic chains.     

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.     

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.     

Facile Synthesis of 2‐Substituted 4‐Azaindoles

A novel and efficient strategy for the synthesis of 2‐substituted 4‐azaindoles from 2‐chloro‐3‐nitropyridine through Pd‐catalyzed Sonogashira cross‐coupling, followed by reduction and heteroannulation on t‐BuOK, is reported.     

Two Efficient Syntheses of Protected 4‐Deoxy‐D‐lyxo‐hexose (4‐Desoxy‐D‐mannose)

The formation of four differently protected 4‐deoxy‐D‐lyxo‐hexose derivatives 7, 8, 12, and 14 is described. In the first procedure, a nucleophilic displacement of the allylic mesylate 4 by hydride was combined with a highly stereoselective osmylation of olefin 6 to afford diol 7. In the second radical procedure, tributyl tin hydride was substituted by the cheap and environmentally friendly hypophosphorous acid as a hydrogen donor in the reduction of xanthate 13 to 4‐deoxy lyxo‐hexose 14.     

Synthesis of Mesoionic 4‐(para‐substituted Phenyl‐5‐2,4‐dichlorophenyl)‐1,3‐4‐thiadiazolium‐2‐aminides by Direct Cyclization via Acylation of Thiosemicarbazides

The synthesis of ten novel mesoionic 4‐[para‐substituted (H, CH₃, OCH₃, NO₂, Cl, Br, OH, t‐C₄H₉, C₆H₅, C₄H₉) phenyl‐5‐2,4‐dichlorophenyl]‐1,3‐4‐thiadiazolium‐2‐aminides, as hydrochlorides, are described. The synthesis strategy utilized the corresponding para‐substituted isothiocyanates as starting materials to obtain the thiosemicarbazides through reaction with phenylhydrazine (61–98%), which were then submitted to acylation with 2,4‐dichloro benzoyl chloride and direct cyclization to generate the desired substituted mesoionic compounds in good yields (ca. 80%).     

Microwave‐Assisted Elimination Reaction of trans‐4‐(4‐Fluorophenyl)‐3‐chloromethyl‐1‐methylpiperidine on Alumina

Abstract

trans‐4‐(4‐Fluorophenyl)‐3‐chloromethyl‐1‐methylpiperidine 3b was subjected to elimination reaction on alumina or KF‐alumina under solvent‐free conditions and microwave irradiation. Compared with the “classical” method of heating in the presence of an organic base, the microwave‐assisted methodology provided higher yields of 4‐(4‐fluorophenyl)‐3‐methylene‐1‐methylpiperidine 7b (65.5–71%) in considerably shorter reaction times (20–40 min). Furthermore, the exocyclic double bond in 7b underwent rearrangement to the endocyclic double bond to furnish compound 8. The effect of alumina and irradiation time on reaction conversion and the extent of isomerization was examined.     

Novel Methods for the Synthesis of 4‐Arylisoquinolinium Perchlorates and 4‐Arylisoquinolin‐1‐ones

2‐Benzylamino‐1‐phenyl‐ethanones 1 were converted to the corresponding isoquinolinium perchlorates 2 in high yields using 70% HClO₄‐FeCl₃ mixture as a cyclization and oxidation reagent. A mild and high yielding method for the oxidation of perchlorates 2 to isoquinolin‐1‐ones 3 involving the treatment of 2 with KOH and K₃[Fe(CN)₆] in THF‐H₂O two‐phase system at room temperature was developed. Compounds 2a–g were shown to be disproportionate to 3 and the corresponding 1,2‐dihydroisoquinoline 4 in the presence of base, which in turn is oxidized by K₃[Fe(CN)₆] to 2.     

Synthesis of Novel Anellated Pyranosides as Precursors of C‐Nucleoside Analogues Using Isopropyl 6‐O‐Acetyl‐3‐deoxy‐4‐S‐ethyl‐4‐thio‐α‐D‐threo‐hexopyranosid‐2‐ulose

Abstract

Isopropyl 6‐O‐acetyl‐3‐deoxy‐4‐S‐ethyl‐4‐thio‐α‐D‐threo‐hexopyranosid‐2‐ulose (3) was converted to the corresponding 3‐[bis(methylthio)methylene] derivative 4 with a push–pull activated C–C double bond. Treatment of 4 with hydrazine and methylhydrazine afforded the pyrano[3,4‐c]pyrazol‐5‐ylmethyl acetates 5a and 5b, respectively. Desulfurization of compound 4 with sodium boron hydride yielded the 3‐[(methylthio)methylene]hexopyranosid‐2‐ulose 7. Compound 7 was reacted with amines to furnish 3‐aminomethylene‐hexopyranosid‐2‐uloses 8, 9. Reaction of 7 with hydrazine hydrate, hydrazines, hydroxylamine, and benzamidine afforded the pyrazolo, isoxazalo, and pyrimido anellated pyranosides (10–13).     

Synthesis of 4‐(Indol‐1‐yl)butanals via Rhodium‐Catalyzed Hydroformylation of 1‐Allylindoles

The rhodium‐catalyzed hydroformylation of new 1‐(β‐methallyl) indoles 1a–e carried out with Rh₄ (CO)₁₂ as the catalyst precursor, at 100 atm total pressure and 100°C, produces the 4-(indol‐1‐yl)‐3‐methylbutanals 2a–e as the sole products in high yields. The synthesized 4‐indolylbutanals are stable under the adopted conditions and are isolated and characterized here for the first time. The preparation of the starting 1‐allylindoles is described too.     

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.     

Synthesis of Potentially Bioactive Heterocycles: Thermal [3,3]Sigmatropic Rearrangement of 4‐(4′‐Aryloxybut‐2′‐ynyloxy)‐6‐methyl‐2‐pyridone

Synthesis of a number of hitherto unreported 4‐aryloxymethylene‐7‐methyl‐2,3‐dihydropyrano[3,2‐c]pyridine‐5‐ones 4a–h have been achieved in moderate yields by the thermal [3,3]sigmatropic rearrangement of 4‐(4′‐aryloxybut‐2′‐ynyloxy)‐6‐methyl‐2‐pyridone.     

Structure and Conformational Mobility of 4′‐Pentyl‐4‐Cyanobiphenyl from IR Spectroscopic Data

The structure and conformational mobility of 4pentyl4cyanobiphenyl in the liquid and liquidcrystal states were investigated by means of IR spectroscopy (experiment and theory). IR absorption spectra in the frequency range 400–4000 cm^-1 were measured in the temperature range 26–150°. Theoretical simulation of the IR spectra was performed using the fragment approach. A comparison of theoretical and experimental spectra showed that the examined samples were mixtures of conformers; characteristics of the most probable conformers are given. Temperaturerelated changes in the spectrum are due to the conformational mobility of the molecules, which is not high in the temperature range considered.