Squaric acid bis

Scheme, 30. Conversion of squaric acid bis(phenyihydrazone) to a dianiiide.

Thermal Rearrangement of Squaric Acid Bis(trimethylsilyl) Ester... 

THERMAL REARRANGEMENT OF SQUARIC ACID BIS(TRIMETHYLSILYL) ESTER... 

Squaric acid bis(sulfonylamidines) from squaric acid diamides... 

Tetra-azabinaphthylene (biquinoxalylene) (237) has been prepared (60%) by flash vacuum pyrolysis (800 °C 0.02 Torr) of the pentacycle (238), and also by reduction of the squaric acid bis-amidine derivative (239), prepared as indicated in Scheme 55. 

The reagent has been employed as a quaternizing agent for a variety of N-heterocycles. Regioselective IV-methylation has been observed (eq 4). Thiazoles are exclusively IV-methylated, whereas tetrazoles yield regioisomeric products. The dication of squaric acid bis(amidine) is prepared by regioselective N-methylation (eq 5). ... 

The bis anion of squaric acid is highly resonance stabilized by four equivalent resonance contributors as well as an aromatic resonance contributor. This results in both protons being easily removed. 

For the sake of completeness, nickel complexes with bis(thiosquaramide) ligands such as [Ni(sq— S4XI2 (sq = squaric acid) (45) are to be noted. They exhibit thermochromic behavior in pyridine solution. Their dinuclear structure is concluded from elemental analyses and spectroscopic data. Complexes such as [Ni(S20—H)2] serve as stabilizers in color photography (46a). They are assumed to exhibit six-coordinate Ni(II) centers. 

The most dramatic synthetic achievement with cyclobutenediones is the synthesis of deltic acid derivatives. As illustrated below, photolysis43 of diethyl squarate (16 d) yielded, among other products, diethyl debate (21). The bis-trimethylsilyl ester (16 e) of squaric acid similarly furnished a deltate ester which was successfully hydrolysed to deltic acid itself (22), the lowest member of the series of oxocarbon acids48). 

Formation of the dianilide of acetylenedicarboxylic acid from still another reaction of 16d, photolysis in ether containing aniline, may involve prior reaction 49) of aniline with 16 d. The bis-anhydride (16f) of squaric acid also afforded an acetylene dicarb-... 

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. 

The reaction mixture is evaporated to dryness under reduced pressure and the squaric acid obtained in 60% yield with respect to absorbed CO after treatment of the solid residue with dilute hydrochloric acid. Reduction of CO has been further confirmed reduction to telomerized radical anions on activated magnesium or calcium oxides has been reported. Reductive coupling of coordinated CO on Nb, Ta, or V complexes gives a coordinated bis(trimethylsiloxy)ethyne ligand. 

Cyclobutane polyhydrazones are accessible from the commercially available squaric acid (47, R = H). The latter, when treated with phenylhydrazine yields a tetrakis(phenylhydrazones) (48), and its butyl ester (47, R = Bu) yields the tris(phenylhydrazone) 49. When squaric acid is oxidized by bromine to cyclobutanetetraone (shown in the tetrahydrated form 50) and treated with phenylhydrazine, it yields the l,3-bis(phenylhydrazone) 51. The tetrakis- and the bis-(phenylhydrazones) exist in the all-hydrazone forms, whereas the tris(phenyl-hydrazone) exists in the azoenehydrazine form 49 (see Scheme 8) 257-261... 

Scheme 12. Structure of 2-oxo-l,3-bis(phenylhydrazono)-cyclohexene, -cyclopentene, and squaric acid tetrakis(phenylhydrazone) in neutral and acid media.258-261 270 271...

Allylations. In reactions using allylsilane as nucleophiles TiCU is one of the most popular catalysts. It is now employed in allylating squaric acid derivatives, 8-phenylmenthyl pyruvate, and (V-acyliminium ions. A remarkable observation is that the four stereocenters of the products from l,8-bis(trimethylsilyl)-2,6-octadiene and two aldehyde molecules are generated with good control. The stereoselective intramolecular reaction is most suitable for the synthesis of bicyclic a-methylene-y-lactones. ... 

Fig.8 Synthesis of bis(trimethylsilyl)squarate from CO and SiMeaCl, with the uranium complex providing electrons for reductive oligomerisation and steric control conversion to squaric acid previously reported...

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

Squaric acid l,2-bis(dimethylamide) warmed with excess p-toluenesulfonyl isocyanate until COg-evolution ceases product. Y 85%. F. e., also from thio-analogs, and 1,3-isomers, s. G. Seitz, R. Schmiedel, and K. Mann, Chem. Ztg. 99, 463 (1975). 

Photoaddition of bis(methylthio)acetylene to a thione gives an a-(thiomethoxy-thiocarbonyl) vinyl sulphide R R C=C(CSSMe)SMe. Vinyl sulphides of particular interest, prepared by straightforward methods, include optically active alkyl vinyl sulphides EtCHMe(CH8) SCH=CHj amides R NHCMe= C(SR )CONHPh and 2-pyridyl vinyl sulphides. The novel sulphur-linked squaric acid analogue (23), prepared from the corresponding thiolate anion by... 

Recent structural studies of squaric acid have shown it to form 1,3-bis(metal) complexes as well as 1,2-bidentate chelates with Ce(III) or with Cu(II). Stopped flow methods have been used to study the reaction between squaric acid and Fe(III). In solutions with [H ] <0.02 M, biphasic absorbance changes are observed due to operation of a number of parallel and series pathways. The initial reactions are complexations to form a 1 1 compound, [Fe(III)(H20)5(squarate)] , and a 2 1 compound, [Fe(III)2(0H)2(H20)6(squarate)] these are followed by a slower reaction leading to the reduction of Fe(III) to Fe(II) by the ligand. The reaction scheme, shown in Eq. (19)-(21), involves monomeric and dimeric squarate... 

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