Macrocycles templated preparation

The use of metals for prearranging reaction centers as neighboring groups has a special value in the production of macrocycles (template effect). Although these ligands can be sometimes prepared directly, the addition of metal ion during the synthesis will often increase the yield, modify the stereochemical nature of the product, or even be essential in the buildup of the macrocycle. There have been few mechanistic studies of these processes. The alkali and alkaline-earth metal ions can promote the formation of benzo[18]crown-6 in methanol ... 

These complexes are rare, doubtless owing to the comparatively ready oxidation of amines. However, the template preparation of Ce(N03)4L-3H20 has been described L is the eighteen-membered macrocycle formed by cocondensation of two molecules of ethylenedi-amine and two molecules of 2,6-diacetylpyridine. The structure of this compound is unknown and it is uncertain to what extent the macrocycle is bonded to the metal ion.689... 

Figure 6-38. The transient template preparation of 6.38. The nickel(u) ion is too small for the cavity of the macrocycle 6.39.

This chapter contains much interesting material relating to the template preparation of macrocycles. 

The synthetic strategy of unsymmetrical BTE-TAPs involved the co-cyclization of bis(3-thiophenyl)maleonitrile and 1,2-dicyanobenzene in different molar ratios under nitrogen atmosphere in the dark, as was described in Scheme 10. Magnesium was a template to gain the unsymmetrical macrocycles. The preparation of the symmetrical phthalocyanine hybrids began with the reaction of magnesium powder... 

Figure 2.19. Early use of a metal template. Ni(II)-templated preparation of macrocycle 50.

The cyclic tetraazadienes were first discovered by Curtis (Curtis, 1960 Curtis and House, 1961). These macrocycles were prepared by reacting 1,2-diaminoethane, 1,2-diaminopropane, or 1,3-diaminopropane with acetone, methyl ethyl ketone, propionaldehyde, n-butyraldehyde, isobutyraldehyde, or other small carbonyl compounds in the presence of Ni(II) or Cu(II) (Blight and Curtis, 1962 House and Curtis. 1962, 1964a, 1964b). Similar tetraaza macrocycles can be isolated from the reaction of triethylenetetraamine and the carbonyl compound in the presence of the metal template ions (Curtis... 

Saccharin, 134, 135, 253, 254, 360, 361 Salicylaldehyde, 411, 412 Salicylaldehyde-metal complex, 99 Schiff-base-containing macrocycles non-template preparation, 412-413,486, 541, 704-708... 

Macrocycles have been prepared by formation of macrocyclic imines as well as by using variations of the Williamson ether synthesis ". Typically, a diamine or dialdehyde is treated with its counterpart to yield the Schiff s base. The saturated macrocycle may then be obtained by simple reduction, using sodium borohydride, for example. The cyclization may be metal-ion templated. In the special case of the all-nitrogen macrd-cycle, 15, the condensation of diamine with glyoxal shown in Eq. (4.14), was unsuccess-ful ... 

We have not attempted to cover all or even most aspects of crown chemistry and some may say that the inclusions are eclectic. We felt that anyone approaching the field would need an appreciation for the jargon currently abounding and for the so-called template effect since the latter has a considerable bearing on the synthetic methodology. We have, therefore, included brief discussions of these topics in the first two chapters. In chapters 3—8, we have tried to present an overview of the macrocyclic polyethers which have been prepared. We have taken a decidedly organic tack in this attempting to be comprehensive in our inclusion of alkali and alkaline earth cation binders rather than the compounds of use in transition metal chemistry. Nevertheless, many of the latter are included in concert with their overall importance. 

It has square planar coordination (Pd-N 2.010-2.017 A) similar to the value of 2.009 A in the tetraphenylporphyrin analogue, prepared by a similar route. As with nickel, macrocycle complexes can be made by in situ template... 

The template-directed preparation of cycloi is(paraquat-4,4 -biphenylene (a molecular square ) has been achieved the use of a macrocyclic hydroquinone-based polyether template incorporating an ester moiety in one polyether chain afforded a 1 1 mixture of two topologically stereoisomeric [3]catenanes <96CEJ877>. 

A new type of calixarene-capped calixpyrrole (9) has been generated (32 %) in one-step from p-fe/t-butylcalix[4]arene tetramethylketone as the template <96TL7881>. A cylindrical calix[4]-fois-cryptand, in which the central calix[4]arene possesses two 1,3-altemating diaza-tetraoxa macrocycles on each face, has been synthesized <96TL8747>. A series of substituted l,4-(2,6-pyridino)-bridged calix[6]arenes has prepared and studied <96LA1367>. 

One of the most successful approaches to the synthesis of metalla-supramolecular systems has been by templated self-assembly processes. Most of the templating agents used by synthetic chemists are either cationic or neutral species. Anions, on the other hand, have only fairly recently been successfully utilized as templates. The new metalla-macrocycles [Pd2Ni2(atu)4(PPh3)4X]3+ (atu = deprotonated amidinothiourea, X = C1, Br, I) have been prepared using anion templated syntheses. Only in the presence of each of these three halides are the metalla-macrocycles... 

A small number of template mediated reactions which afford thioether macrocycles are also known, e.g. the small trithia [9]aneS3 is also obtained in good yield using Mo(CO)3 as a template.73,74 The crown trithioether is readily demetallated by addition of a further equivalent of [NMe4]2[S(CH2)2S(CH2)2S]. Also, dibenzo-[18]aneS6 and dibenzo-[15]aneS5 have been prepared via an iron dicarbonyl template.75,76 Metal-induced cyclo-oligomerization reactions of... 

Porphyrazines (pz), or tetraazaporphyrins, are compounds that can be viewed as porphyrin variants in which the meso carbon atoms are replaced with nitrogen atoms, as Fig. 1 shows (1). This difference intrinsically gives porphyrazines discrete physiochemical properties from the porphyrins. In addition, despite their similar molecular architecture, porphyrazines are prepared by an entirely different synthetic route than porphyrins—by template cyclization of maleonitrile derivatives, as in Fig. 2, where the open circle with the A in it represents the peripheral substituent of the pz—rather than by the condensation of pyrrole and aldehyde derivatives (1). The pz synthetic route allows for the preparation of macrocycles with chemical and physical properties not readily accessible to porphyrins. In particular, procedures have been developed for the synthesis of porphyrazines with S, N, or O heteroatom peripheral functionalization of the macrocycle core (2-11). It is difficult to impossible to attach the equivalent heteroatoms to the periphery of porphyrins (12). In addition, the preparation and purification of porphyrazines that bear two different kinds of substituents is readily achievable through the directed cocyclization of two different dinitriles, Fig. 3 (4, 5, 13). 

The first stage in the preparation of the octapyridylporphyrazine is the synthesis of Mg[pzpy8] (40, Scheme 8) (20%) by the Mg-templated macrocyclization of bis(4-pyridyl)maleonitrile (39). Demetalation forms the octapyridylpz (41), which... 

Synthesis. The first example of a stable, soluble pz peripherally substituted with a heteroatomic moiety involved appended thioether groups, M[pz(.V-Mc)8, as reported in 1980 by Schramm and Hoffman (2) (Scheme 9, 45-48). Mg[pz(5 -Me)s], 46, was prepared in a 60% yield by a magnesium templated macrocyclization of dinitrile, 45. Demetalation with sulfuric acid gave H2[pz(5 -Me)8], 47 (65%) and remetalation with the anhydrous acetate salts of copper and nickel gave 48 (80%) and 49 (65%). 

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