Biphenylene-diols

An alternative strategy for promoting Diels-Alder reaction by proton involves the activation of dienophile by hydrogen bonding [93]. Biphenylene diol 143 (Scheme 4.26) forms doubly hydrogen-bonded complexes with a,j]-unsaturated carbonyl compounds, which strongly accelerate the Diels-Alder... 

Fig. 10.19 Interaction orbitals responsible for electron delocalization from the oxirane part to the acid part in the 1 1 complex of oxirane and an acid. The orbital ( ) s are given by the combination of the occupied MOs of the oxirane part, and F s are given by the combination of the unoccupied MOs of the acid part. Two orbital pairs on the left-hand side are for the (oxiiane+l,8-biphenylene-diol) system and a pair on the right-hand side is for the (oxirane + phenol) system [51]...

Mine [7] and Kelly [8] were the first to prepare synthetic equivalents of this bidentate motif, using biphenylene diols as catalysts. Shortly after Etter had studied the hydrogen bonding patterns in supramolecular assemblies of various carbonyl compounds [9, 10], Curran introduced diarylurea derivatives as further bidentate organocatalysts [11, 12]. This interplay between supramolecular chemistry and non-covalent catalysis has turned out to be very fruitful ever since [13-15]. Schreiner subsequently showed that thioureas are also potent organocatalysts, which offer several advantages compared to urea derivatives, e.g., better solubility [13, 16]. In a proof-of-principle study, thiourea derivative 1 (Fig. 1, right) was used to catalyze the Diels-Alder reaction shown in Scheme 1 [16]. 

The materials employed in these formulations consisted of bitolylene diisocyanate (3,3 -dimethyl-4,4 -biphenylene diisocyanate, 136T Upjohn Co.) referred to as T0DI, a polyether diol (tetramethyleneoxide polyol, Polymeg 2000, Quaker Oats Co.), a polyester diol (caprolactone polyol, PCP-200, Union Carbide Corp.) and a chain extender, 1,4-butanedio1 (Aldrich Chemical Co.). The formulations were prepared by a two-step procedure. In... 

Another example of such a type of polyester is shown in Fig. 4. The polyester po-ly(2,2 -dimethyl-4,4 -biphenylene-phenyl-terephthalate) derived from 2,2 -dimethyl-biphenyl-4,4 -diol (BDMDH) and phenyl-terephthalic acid forms a nematic melt. Crystallization from the melt is completely... 

Versions with diacid, diol and di-ester substituents have been patented [111] which are suitable for reacting into aromatic polyesters, as have stabilisers with suitable substituents to allow dispersion or dissolution in dye baths for impregnation into fibres or textiles [113,114,116]. Other related species include those with biphenylene groups on the 4- and 6-positions on the triazine core [119], naphthalene groups on 4 or on both 4 and 6 [120], 1,2,3,4-tetrahydronaphthalene on 4 and 6 [124], and 2-hydroxynaphthalene on the 2-position [125]. Versions with longer side chains than hexyl or octyl have also been synthesised, and it is claimed that these have increased compatibility with their host polymer [121, 127]. 

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