Squaric acid dichloride

Symmetrical, aniline-based, and aromatic oxo-squaraines are synthesized via a one-step reaction by heating two equivalents of the appropriate /V,/V-dialkylaniline or other reactive aromatic or heteroaromatic derivatives with squaric acid (Fig. 6) [38, 41]. Unsymmetrical aniline-type squaraines can be synthesized in two steps first one component is reacted with squaric acid dichloride to yield a mono-squaraine intermediate, which in a subsequent step is then reacted with the second component to yield the unsymmetrical squaraine dye [53]. 

Other electrophilic substitution reactions on aromatic and heteroaromatic systems are summarized in Scheme 6.143. Friedel-Crafts alkylation of N,N-dimethyl-aniline with squaric acid dichloride was accomplished by heating the two components in dichloromethane at 120 °C in the absence of a Lewis acid catalyst to provide a 23% yield of the 2-aryl-l-chlorocydobut-l-ene-3,4-dione product (Scheme 6.143 a) [281]. Hydrolysis of the monochloride provided a 2-aryl-l-hydroxycyclobut-l-ene-3,4-dione, an inhibitor of protein tyrosine phosphatases [281], Formylation of 4-chloro-3-nitrophenol with hexamethylenetetramine and trifluoroacetic acid (TFA) at 115 °C for 5 h furnished the corresponding benzaldehyde in 43% yield, which was further manipulated into a benzofuran derivative (Scheme 6.143b) [282]. 4-Chloro-5-bromo-pyrazolopyrimidine is an important intermediate in the synthesis of pyrazolopyrimi-dine derivatives showing activity against multiple kinase subfamilies (see also Scheme 6.20) and can be rapidly prepared from 4-chloropyrazolopyrimidine and N-bromosuccinimide (NBS) by microwave irradiation in acetonitrile (Scheme... 

M. M. Krayushkin, V. Z. Skirinian, L. I. Belen kii, A. Y. Shadronov, L. G. Vorontsova, Z. A. Starikova, Photochromic dihetarylethenes 13. Optimization of conditions for the acylation of 2,5-dimethylthiophene with squaric acid dichloride, Russ. Chem. Bull, 51, 1510-1514 (2002). 

Squaric acid formed polymer 87 with titanocene dichloride.172-175 IR and Raman spectra of the systems were very similar to the starting spectra with the exception of the formation of Ti-O and loss of —OH stretching bands. 

M. Williams, C. Carraher, F. Medina, M. Aloi, Comparative Raman and Infrared Vibrational Study of the Polymer Derived from Titanocene Dichloride and Squaric Acid, in Structure-Property Relations in Polymers, M. Urban, C. Craver, Eds., p. 769-776, American Chemical Society, Washington, DC, 1993. 

M. Williams, C. Carraher, Comparative Infrared and Raman Spectroscopy of the Condensation Product of Squaric Acid and Bis(cyclopentadienyl)titanium Dichloride, in Inorganic and Metal-Containing Polymeric Materials, J. Sheats, C. Carraher, C. Pittman, Jr., M. Zeldin, B. Currell, Eds., pp. 295-318, Plenum Publishing, New York, 1995. 

Squaric acid diesters react with 2- or 4-substituted pyridinium, quino-linium, and benzothiazolium iodides to yield 1,2-disubstituted dyes [16] (Structure 1). 1,2-Disubstituted dyes were also synthesized using Friedel-Crafts reaction of squaraine dichloride with various nucleophiles as a key step [27]. 

COMPARATIVE INFRARED AND RAMAN SPECTROSCOPY OF THE CONDENSATION PRODUCT OF SQUARIC ACID AND BIS(CYCLOPENTADIENYL)TITANIUM DICHLORIDE... 

We recently synthesized the interfacial condensation product of biscyclopentadienyltitanium IV dichloride, Cp2TiCl2, and the disodium salt of squaric acid. 

Sodium ethoxde Natronkalk Soda lime Oxydation Oxidation Peressigsaure Peroxyacetic acid Phenyljodidchlorid lodobenzene dichloride Polymerisierung Polymerization Quadratsaure Squaric acid... 

The derivatization method is compensated by the electrophihc addition reaction using organosilicon reagents [40-43]. Thus, the squaric acid family of derivatives, e.g., dichloride 17, methyl ester chloride 18, amide chloride 19, and diester 5 are the partners of the reactions with allylsilanes, silyl enol ethers, and silyl ketene acetals (Scheme 3). In this case, 1,2- and 1,4-addition to 20 and 21, respectively, are regulated by the substitution pattern of unsaturated organosilanes, kind of Lewis acid catalysts, and the reactivity of acid derivatives. The less congested is the reaction site, the more preferable is 1,2-... 

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