Ansa compounds

Bis-ansa compound obtained from cyclooctadecane-l,9-dione. 

Inclusion of electron-deficient subrings is accomplished by reaction of dione (61) with hydrazine, followed by dehydrogenation (74JA5287). Oxidation of (73) with peroxybenzoic acid affords the mono-AC-oxide (74), a chiral ansa compound. 

A small ring current was described for 1,4-dodecamethylene benzene [83], The most shielded methylene carbons of this ansa compound shift upheld by 0.7 ppm relative to those in cyclopentadecane ... 

Figure 2.7 Stereoelectronic explanation of the preferential reaction of many pyridoxal ansa compounds on their seemingly more hindered faces. (Reprinted from Ref. 47. Copyright 1994 American Chemical Society.)...

A p-anilyl-substituted an.va-titanocene 48 and titanocene 3 were tested on the growth of a wide variety of tumour cells in vitro on a panel 36 human tumour cell lines containing 14 different tumour types investigated in a cellular proliferations assay [34]. Titanocene 3 showed a significantly higher cytotoxic activity than the ansa-compound and reached, on average over the whole cell panel, the activity of cisplatin within a factor of 4. Nevertheless, there were three main targets for titanocene 3 identified, which are pleura mesothelioma, uterine and renal-cell... 

The reactions of N3P3C16 with ethylenediamine and ethanolamine give spirocyclic derivatives (25) and not ansa-compounds. Aliphatic and alicyclic diols also yield spirocyclic derivatives (26, 31). Inclusion clathrates formed by spirocyclic phosphazenes with aryldioxy substituents (2) have been studied by mass spectrometry, broadline NMR, and X-ray techniques (4). Some conclusions on molecular motion in these compounds have been deduced. 

A plane of chirality is encountered in molecules in which a molecular plane is desymmetrized by a bridge (ansa compounds and analogs). Examples include the paraphane derivatives XXXV and XXXVI, and wwts-cycloalkenes (XXXVII). 

Besides the bis(indenyl) ansa compounds, C2 symmetric bridged bis(cyclo-pentadienyl) metallocenes of zirconium and hafnium were found to be able to produce isotactic polypropene (Table 8) [103]. The key for high isotaeticity are substituents in positions 2,4,3 and 5 generating a surrounding of the transition metal similar to the one in bis(indenyl) metallocenes. 

The reaction of 6,6-diphenylfulvene with Ti atoms to give the tuck-in bis-Gp derivative (ATT = —136.8 kcal mol-1) and the reaction of 6-diphenylfulvene with TiCl2 to afford the trans-[( 1,2-diphenyl-1,2-dicyclopentadienyl)ethanediyl] dichloro Ti(iv) ansa-compound (A//= —114.4 kcal mol-1) (Scheme 551) have been studied and the corresponding reaction enthalpies have been calculated.1... 

The unsymmetrical ansa-compound Me2C(3-C5H3But)(3-G9H5But)TiCl2 has been synthesized and the isomers separated by repeated recrystallizations.1646... 

A few other variations are included here to demonstrate the diversity of this class with regard to molecular shape. Vogtle et al. s multiple ansa compound (115, R = CH2CH2OCH2CH3), an unexpected product obtained from an attempt to synthesize biscalixarenes with aromatic linkers, has two bridges threaded through the macrocycle formed by joining the two calixarenes subunits [152]. Siegel et al. s... 

More than 90 years after the first reported synthesis of [2.2]metacyclophane [1] and nearly 50 years after the synthesis of [2.2]paracyclophane, [2] cyclophane chemistry is still a field of ongoing research. In the beginning, work had been focused on the development of new synthetic methods yielding cyclophanes and ansa-compounds and the investigation of their physical properties. Later, the scope was extended to the incorporation of heterocycles into phanes and the more sophisticated techniques allowed the synthesis of multibridged and multilayered phanes. All this has been extensively reviewed [3]. 

Although the chirality of cydophanes was recognized more than 50 years ago by Liittringhaus and Gralheer in ansa compounds [14], chiral cydophanes have been applied as auxiliaries and ligands in asymmetric synthesis only recently. Some examples of this exciting use of cydophanes will be given. 

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