Tolanes, also

Small chemical changes to the tolane family of mesogenic molecules are also known to bring about major changes in phase behaviour [22]. Two examples are shown in Fig. 5 where subtle changes in the tail can eliminate the nematic phase. 

Additionally, DMS induces apoptosis by increasing intracellular sphingosine levels as demonstrated in platelets (Yatomi et al, 1996). However, it should be noted that the SPHK inhibitors DMS and threo-DHS also inhibit PKC (Haimun and BeU, 1989), which may contribute to some of their observed effects (Tolan et al., 1999). 

DiphBnylacetylene. The photophysics and photochemistry of diphenyla-cetylene (DPA), also known as tolan, and several derivatives have been reviewed. The unusual photophysical properties, such as a very slow rate of conversion of S2 to 5i, a dependence of the S2 lifetime on temperature, and a strong dependence of excitation wavelength on the fluorescence quantum yield of the lowest excited singlet states of DPA were correlated with the 5 2-5 i energy gap. 

Orgel (23). Subsequently, Hubei and co-workers (24) obtained, among other products, tricarbonyl-7r-tetraphenylcyclobutadiene iron by the reaction of tolane with iron carbonyls. More recently, a general synthesis of tetra-phenylcyclobutadiene-metal complexes using ligand transfer from tetra-phenylcyclobutadiene palladium(II) halides (25) to a metal carbonyl has been described (26). It is also possible to obtain complexes containing... 

The black trinuclear iron complex Fe3(CO)8(Ph2C2)2> one of two isomers obtained by the reaction of excess tolane with dodecacarbonyl iron, contains not only a heterocyclic iron atom similar to that first observed by Hock and Mills (36) but also has two iron atoms lying symmetrically on either side of the heterocyclic ring (42) in a manner similar to that suggested by the author on theoretical grounds (20) (Fig. 9). 

The preparation of the related high molecular weight poly-1.4-phenylene sulfide has been accomplished by heating />-bromothio-phenolate salts in pyridine at 250° C (57). The commercially available polyethersulfones are reported to be prepared by condensation of 4.4 -dichlorodiphenyl sulfone with salts of biphenols in solvents such as dimethylsulfoxide at 150° C. The work of Bacon and Hill would suggest that both of these reactions might be carried out at considerably lower temperatures with copper (I) salts as catalysts. In addition, it has been demonstrated that copper (I) acetylides react quantitatively with aromatic iodides to yield tolanes (15, 77) therefore this reaction should also be the basis for a similar polymer forming reaction. 

Apart from further stilbenes23 containing sulfonic acid groups, reaction has also been observed with methyl-substituted tolans,21,24 bi-and terphenyls,21,22 naphthalenes,21,22,25 anthracenes,21,22 phenan-threnes,21,22 and even benzenes,21,22 whereby up to four methyl groups can be brought to react. 

Benzal chloride also splits off hydrochloric acid, but no chlorine a mixture of a- and / -tolane dichlorides results ... 

Other related dendrimers of the first [279] and second [280] generation based on the 1,3,5-triazine unit and tolane arms were also reported by Lee and Yamamoto. The dendrimers of the first generation bearing two chains exhibit a Colh phase as expected. Surprisingly, the members of the second generation also showed a Colh phase between 130 and 150 up to 170-230 °C, despite of the grafting of only one terminal chain per peripheral arm. 

The reader may remember that the 77-complex structure for the adducts formed from acetylene and mercury dichloride, or of related complexes of non-transitional-metal halides, was disproved by our stereochemical investigations. The true 77-complexes, however, were also obtained by us from tolan and the derivatives of such transition metals as V, Nb, and Ta (451-455). 77-Cyclopentadienylniobium tetracarbonyl reacted with tolan according to the scheme shown on page 57. 

We found also that (77-C5H,)V(CO)3PPh3 as well as its niobium analog, when irradiated, underwent substitution of one PPh3 and one CO by tolan. Hence, niobium (and tantalum) complexes of the type are able to attach a third molecule of tolan and transform this to hexaphenylbenzene, unlike the vanadium analog, which transforms just two tolans to tetraphenyl-cyclobutadiene or, if irradiated, combines them with carbon monoxide and produces tetraphenylcyclone. 

The trimerization reaction with benzene derivatives could sometimes follow a similar path but, since it also occurs with disubstituted acetylenes such as HOCH2C = CCH2OH, some other mechanism must also be operating. Schrauzer explained the cyclization of tolane with a catalyst based on bisacrylonitrilenickel and triphenylphosphine by the so-called V-complex, multicenter processes. With this process, three alkyne molecules would successively coordinate with nickel and then the ring closure would take place (See Figure 6). 

The reaction of aryl halides 1 with alkynylcopper(I) 2 under reflux in pyridine to prepare internal arylacetylenes is known as the Stephens-Castro reaction [Eq. (1)] [2]. The reaction has proved to be particularly important in the synthesis of a wide range of tolan and heteroaromatic alkynes [3]. Vinyl and allenic halides can also be used and several reviews... 

Bcnzynes.s LiTMP is also an effective base for formation of benzynes from ArCl. Thus treatment of o-chloroanisole with LiTMP and LiC=CC6H5 gave m-rneth-oxytolane (1, tolane = diphenylacetylene) in 80% yield. Diphenyl sulfide was prepared in 93 % yield from C6H5C1, C6H5SLi, and LiTMP. 

Mercury has also been inserted into the bridge of donor-acceptor chromophores and affords increased transparency relative to comparable all-organic bridges thus, a /3-value of 26 X 10 esu has been reported for 195 (Figure 16), compared to values of 24 and 28 x 10 esu for corresponding tolane (compound 195 minus the Hg) and bis(phenyl)-butadiyne analogs, respectively, while the absorption maxima are 307 nm for 195 and 379-384 nm for the all-organic... 

As well as undergoing addition to enones, arenes, carbonyl groups and thiocarbonyl groups, alkynes also undergo additions to alkenes. Thus tolan affords cyclobutenes on photoaddition to the tetrahydronaphthalene 126. The triplet-sensitized irradiation of vinylacetylene in the presence of 1,1-dichloroethene yields the (2 + 2)-cycloadduct 127 as well as the dimers 128 and 129. Similar behaviour is observed when dienes are the reaction... 

Recently Ribeiro et al. [65] reported on the synthesis and characterization of a variety of tolanes that had optically active sulfinate groups. Some of these compounds, see 23, were found to possess a phase that exhibited oily-streak textures typical of chiral nematic phases and also defect pattern associated with columnar phases (the earlier photomicrograph Plate 6 for 14P1M7 is similar). 

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