Squaric acid derivative

Highly selective synthesis of polyfunctionalized heterocycles based on ring expansion of squaric acid derivatives 97YGK785, 98SL1167. 

As a possible source for new long-wavelength dye systems, biradicaloid dyes possessing energetically close-lying frontier molecular orbitals could be used. 146 An example of such dye systems already in extensive use in imaging are squaric acid derivatives like SQ. 147, 14S ... 

The same mechanism is operative for the preparation of squaric acid derivatives of type 112. Treatment of 3,4-dicMorocyclobutene-l,2-dione with two different zinc-copper reagents provides the double addition-elimination product 112 in 67% yield (Scheme 2.41) [87]. 

A final example illustrates the use of squaric acid derivatives in enzyme inhibition. In an effort to discover potent inhibitors (of Yersinia PTPs and PTPIB) with reduced charge and thus improved bioavailabihty, Xie et al. (53) also studied the squaric acid motif as a nonhydrolyzable phosphotyrosine mimic. 3-aryl-4-hydroxy-3-cyclobutene-l,2-diones based on the... 

A squaric acid derivative which is also an arsonium ylide has been made (equation 33) ". ... 

This addition-elimination reaction can be applied to the preparation of squaric acid derivatives. Thus, the treatment of 3,4-dichlorocyclobutene-l,2-dione 27 with two different zinc-copper reagents furnishes polyfunctional squaric acid derivatives like 28, provided the first zinc-copper reagent bears a secondary or tertiary alkyl group (Scheme 9-26) [56]. 

Diketones. Squaric acid derivatives are converted to the diketones after reaction with RLi and quenching with NH Cl. 

By explaining these templates in detail, we will show their possibilities as key intermediates for the synthesis of a large range of different core structures. Tempest and Armstrong [11] have introduced the term Multiple Core Structure Libraries (MCSL) for resin-bound squaric acid derivatives. 

Tempest and Armstrong [11] have introduced squaric acid as a template for the generation of MCSLs. Starting from squaric acid derivatives, different carbo- and heterocyclic compounds can be generated (Scheme 6.4). 

The synthesis of substituted squaric acid derivatives was shown in two other reactions. In one synthesis, the educt shown in Figure 6.2 was used the isopropoxy group was displaced with different secondary amines and the products were cleaved from the resin. 

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. ... 

Deltic acid (242a) has been prepared via the photochemical decarbonylation of the squaric acid derivative (243) in hexane solution using a Vycor filter to... 

Cleavage of cyclobutenolones/ Squaric acid derivatives undergo oxidative... 

A quinone methide is a probable intermediate in the formation of dimethylnaphthylgeranine E, which involves a photoannulation of a 2-aryl-3-alkoxy-1,4-naphthoquinone, itself formed by thermal rearrangement of a squaric acid derivative <97JOC5658>. The thermal decomposition of chroman which leads to o-quinone methide has been studied <97JOC4804>. 

Aromatic amines react with (420) to give the substitution product (421). The structure was established by 2f-ray diffraction studies. West has reported the formation of a binuclear sulphur-bridged squaric acid derivative (423) from the dimerization of (422) in presence of copper(ii). ... 

Oxocarbenium ions derived from squaric acid derivatives have also been intercepted with 3-[(trimethylsilyl)methyl]-3-butenoic acid methyl ester. The ensuing adducts are converted into bicyclo[3.2.0]heptenones (eq 4) upon thermolysis. Related chemistry has been employed in the trapping of a thiacarbenium ion annulated to a Cgo core. ... 

Tempest and Armstrong were successful in coupling squaric acid derivatives to aryl halides using either a Stille coupling or direct metallation of the resin bound aryl halide and subsequent addition to the... 

Squaric acid derivatives display a marked proclivity to crystallize in noncentrosymmetric space groups, meaning that such compounds can exhibit NLO properties in the bulk. 5-Amino-2-methoxypyridine ester amide of squaric acid ethyl ester crystallizes in the noncentrosymmetric space group C,. without the help of additional chiral agents. This form we will describe as solid phase 1. Its electronic nonlinearity is based on molecular units containing a strongly delocalized n-electron system with donor and acceptor groups at opposite ends of the molecule, which could explain the SHG results [280,281]. The molecule of 5-amino-2-methoxypyridine ester amide of... 

Spassova, M., T. Kolev, and I. Kanev. 2000. Structure and nonlinear electrical properties of squaric acid derivatives a theoretical study of the conformation and deprotonation effects. J. Mol. Struct. THEOCHEM52 151-159. 

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