Synthesis and characterization of two isomeric liquid crystal series with reactive double bonds

Two series of potentially cross-linkable liquid crystal materials derived from p-phenylenebisacrylic (series I, n(P.FB.P), n = 2-10) and p-hydroxycinnamic acid (series II, n(HC.T.HC), n = 2-10) have been synthesized and their thermal and mesomorphic properties studied. All these compounds show enantiotropic mesomorphism over a wide range of temperatures. Compounds with short terminal chains are nematic and when the terminal chain length is increased they show smectic polymorphism-smectic A and C. Most of the compounds are thermally stable over their mesophase ranges.     

Synthesis of isomeric triazolopyrrolopyrimidines

4‐Hydrazino‐7H‐pyrrolo[2,3‐d]pyrimidines ( 4 ) were cyclocondensed with formic acid or triethyl orthoformate to give 7H‐1,2,4‐triazolo[1,5‐c]pyrrolo[3,2‐e]pyrimidines ( 5 ) and 7H‐1,2,4‐triazolo[4,3‐c]pyrrolo‐[3,2‐e]pyrimidines ( 6 ) respectively. The [4,3‐c]‐isomers ( 6 ) were rearranged into thermodynamically more stable [1,5‐c]‐isomers ( 5 ). The identical compounds ( 5 ) were prepared using another route by reacting 3‐amino‐4‐imino‐7H‐pyrrolo[2,3‐d]pyrimidines ( 3 ) with formic acid or triethylorthoformate. Reaction of 2‐amino‐3‐cyanopyrroles ( 1 ) with triethyl orthoformate followed by hydrazinolysis afforded ( 3 ) via the formation of N‐ethoxymethylene‐2‐amino‐3‐cyanopyrroles ( 2 ).     

Synthesis and structures of isomeric benzobisthiazoles

It is shown that the bases described in a number of papers and patents as 2,6-dimethyl-, 2,6-diamino-, and 2,6-dimercaptobenzo[1,2-d:4,3-d']bisthiazoles (isomers of linear structure) are actually 2,7-dimethyl-, 2,7-diamino-, and 2,7-dimercaptobenzo [1,2-d:6,5-d']bisthiazoles (isomers of angular structure). The synthesis of the hitherto unknown 2,6-dimethylbenzo[1,2-d:4,5-d'] bisthiazoles is described.     

Synthesis and structures of isomeric benzobisthiazoles

It is shown that the bases described in a number of papers and patents as 2,6-dimethyl-, 2,6-diamino-, and 2,6-dimercaptobenzo[1,2-d:4,3-d']bisthiazoles (isomers of linear structure) are actually 2,7-dimethyl-, 2,7-diamino-, and 2,7-dimercaptobenzo [1,2-d:6,5-d']bisthiazoles (isomers of angular structure). The synthesis of the hitherto unknown 2,6-dimethylbenzo[1,2-d:4,5-d'] bisthiazoles is described.     

Synthesis and interconversion of isomeric pyrrolotriazolopyrimidines

4‐Hydrazino‐7H‐pyrrolo[2,3‐d]pyrimidines 4 were cyclocondensed with formic acid or triethyl orthoformate to give 7H‐pyrrolo[3,2‐e][1,2,4]triazolo[1,5‐c]pyrimidines 6 and 7H‐pyrrolo[3,2‐e][1,2,4]triazolo[4,3‐c]pyrimidines 7 , respectively. The [4,3‐c] isomers 7 were rearranged into thermodynamically more stable [1,5‐c] isomers 6 . The identical compounds 6 were prepared using another route by reacting 3‐amino‐4‐imino‐7H‐pyrrolo[2,3‐d]pyrimidines 3 with formic acid or triethyl orthoformate. The reaction of 2‐amino‐3‐cyanopyrroles 1 with triethyl orthoformate gave N‐ethoxymethylene‐2‐amino‐3‐cyanopyrroles 2 . Further reaction with an equivalent of hydrazine hydrate provided 3‐amino‐4‐imino‐7H‐pyrrolo[2,3‐d]pyrimidines 3 , whereas treatment with excess of hydrazine hydrate, 3 rearranged to 4‐hydrazino‐7H‐pyrrolo[2,3‐d]pyrimidines 4 . Compounds 4 were also obtained by the treatment of N‐ethoxymethylene‐2‐amino‐3‐cyanopyrroles 2 in excess of hydrazine hydrate. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:265–273, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20295     

Synthesis and properties of two new series of isomeric liquid crystalline polyesters with conjugated double bonds

Two homologous series of flexible main chain liquid crystalline polyesters with isomeric mesogenic groups containing conjugated double bonds, were synthesized and studied by differential scanning calorimetry and optical microscopy. One series (S1) has the p-phenylene-diacryloyloxydibenzoyl moiety as a mesogenic unit. The other (S2) has the terephtaloyl dioxydicinnamoyl moiety as a mesogenic unit. The reactivity of the conjugated double bonds of the p-phenylenediacryloxy unit, at the temperature of mesophase formation, impedes the stability of liquid crystalline mesophases of polymers of series (S1). Two low molecular weight analogues of polymers were also prepared and their properties compared with those of polymers of similar structure. The two model compounds form stable smectic mesophases over a wide range of temperatures, which shows the high mesomorphogenic ability of both mesogenic units.     

Synthesis of two isomeric dimethylthiazolophenothiazines

Two condensed four-ringed heterocyclic bases—2, 10-dimethylthiazolo[4, 5-b]phenothiazine and 2, 6-dimethylthiazolo[4, 5-c]pheno-thiazine-have been synthesized. The structure of the new heterocycles has been confirmed by their IR and UV spectra.     

Synthesis of isomeric β-haloethylthienopyrroles

The preparation of ethyl 4-(2-bromoethyl)thieno[2,3-b]pyrrole-5-carboxylate and ethyl 6-(2-bromoethyl)thieno[3,2-b]pyrrole-5-carboxylate by reaction of t-butyl 2-(2-thienyl)carbazate and t-butyl 2-(3-thienyl)carbazate with ethyl-5-bromo-2-oxopentanoate are described.     

Synthesis of isomeric fluoronitrobenzene-sulfonyl chlorides

The synthesis of five hitherto unknown isomeric fluoronitrobenzenesulfonyl chlorides is described. The compounds are prepared from difluoronitrobenzenes by a two-step procedure. In the first step the starting compounds undergo a regioselective reaction with phenylmethanethiol giving rise to the corresponding thioethers. The oxidative cleavage of the latter with chlorine results in the sulfonyl chlorides in good yields. One example of a threefold sequential functionalization of 2-fluoro-6-nitrobenzenesulfonyl chloride showing the synthetic utility of the title compounds is provided.     

Synthesis and characterization of isomeric diphenylphosphatoisosorbide acrylates

Abstract

Isosorbide is a diether diol readily available from starch, an abundant, renewable biomaterial. Because of its structure and functionality, it may serve as a base for the development of nontoxic polymer additives, particularly flame retardants. Conversion of one of the hydroxyl groups to a diphenylphosphato moiety followed by conversion of the other to an acrylate affords isomeric vinyl monomers suitable for copolymerization with a variety of monomers to generate flame-retardant polymers.     

Synthesis of isomeric benzodipyrrolenines and their derivatives

The Fischer reaction was used to synthesize 2,3,3,5,5,6-hexamethyl-3H,5H-benzo[1,2-b5,4-b]dipyrrole and 2,3,3,7,8,8-hexamethyl-3H,8H-benzo[1,2-b3,4-b]dipyrrole from the dihydrazone obtained by the action of methyl isopropyl ketone on m-phenylenedihydrazine. Centrosymmetrical 2,3,3,6,7,7-hexamethyl-3H,7H-benzo[1,2-b4,5-b]dipyrrole was synthesized from p-phenylenediamine and methyl bromoisopropyl ketone. Mono- and diquaternary salts were obtained from the new bases. The diquaternary salts were converted to bismethylene bases.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 614–617, May, 1971.     

Synthesis and conformational analysis of isomeric 3-propananilidotropanes

The isomeric 3-anilino and 3-propananilidotropanes have been synthesized and obtained in isomerically pure form. The configurations and solute conformations of these isomers were studied via glc and nrar analysis. The 3β-isomers have been shown to exist in the normal piper-idine chair conformation whereas the 3α-anilino tropane exists in a flattened piperidine chair conformation and the 3α-propananilidotropane isomer preferentially exists in a conformation in which the piperidine ring system is a boat.     

Synthesis and structural analysis of isomeric pyridinophanes and thiacyclophanes

A one-pot synthesis of structurally isomeric tetrathiacyclophanes through four-centre coupling reactions of suitable bromides and thiols is reported. The structures of the isomers were confirmed by spectroscopy and XRD analysis. Single crystal X-ray analysis reveals interestingly shaped molecular structures with large cavities.     

Synthesis and optical properties of isomeric branched pi-conjugated systems

[structure: see text] Branched conjugated systems with a terminal alkyne function have been prepared starting from 4-(triisopropylsilylethynyl) phenylacetylene by applying the following iterative reaction sequence: (i) metal-catalyzed cross-coupling reaction of the terminal alkyne with 3,4-dibromobenzaldehyde or 2,5- dibromobenzaldehyde; (ii) Corey-Fuchs dibromoolefination and treatment with an excess of LDA. The building blocks thus prepared have been subjected to a Pd-catalyzed cross-coupling reaction with 1,4-diiodobenzene to yield isomeric branched pi-conjugated systems containing 7 (first generation) or 15 (second generation) phenyl units connected by ethynyl spacers. The different pi-conjugation patterns in those isomeric derivatives have a dramatic effect on their electronic properties, as attested by the differences observed in their absorption and emission spectra. Finally, theoretical calculations have been performed to rationalize the optical properties of these compounds.     

Synthesis and separation of racemic, isomeric desoxo-demethyl-cassaine derivatives

For the synthesis of analogues of Erythrophleum alkaloids the tricyclic ketones 3 (trans-anti-trans) and 5 (trans-anti-cis) were prepared. Reaction of 3 and 5 with triethyl phosphonoacetate led to a mixture of cis/trans compounds, which could be separated in a preparative scale into the uniform racemic isomers 8 and 9, 22 and 23 , respectively. Transesterification of these compounds gave the corresponding 2-dimethylamino-ethyl esters.     

Synthesis,structure, and properties of isomeric polyaminoacetophenones

In terms of the ability for electrochemical transformations in acidic medium, the reactivity decreases in the order o-aminoacetophenone > p-aminoacetophenone > m-aminoacetophenone > aniline. The products of electrochemical polycondensation of the ortho and para isomers are conductors. Oxidative polycondensation of o-aminoacetophenone forms emeraldin hydrosulfate, and with p- and m-aminoacetophenones, emeraldin and leucoemeraldin are formed. In terms of thermal stability, polyacetoaminophenones can be ranked in the order poly-o-aminoacetophenone > poly-m-aminoacetophenone > poly-p-aminoacetophenone.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 12, 2004, pp. 2012–2018.Original Russian Text Copyright © 2004 by Stratan, Kovalchuk, Blazejowski.This revised version was published online in April 2005 with a corrected cover date.     

Synthesis and characterization of isomeric cis- and trans-pyrrone model compounds

Isomeric cis- and trans-imidazopyrrolones, obtained from the reaction of pyromellitic di-anhydride and o-phenylenediamine, were prepared as models for pyrrone polymers. The characterization of these model compounds, which represent the repeat unit of the completely cyclized polymer, provided information which could not be obtained by studying the polymer itself. Isomerism was proven by the nuclear magnetic resonance spectra of soluble ester-benzimidazole derivatives. This study indicated that a single band around 1755 cm^?1 should appear in the infrared spectrum of the completely cyclized polymer. The high melting points of the model imidazopyrrolones indicate the extreme thermal stability to be anticipated from perfectly formed pyrrone polymers.