Heteroatomic functionalized substituents

A cyclopentadienylmagnesium bromide containing a heteroatom-functionalized substituent at the cyclopentadienyl group has also been structurally characterized. When l-[2-(dimethylamino)ethyl]-2,3,4,5-tetramethylcyclopentadienylmagnesium bromide is recrystallized from dichloromethane, dimeric [(Mc2N(CH2)2)Me4C5MgBr]2 (206) (Figure 88) is obtained. Its X-ray crystal-structure determination reveals a structure in the solid state... 

Chemical synthesis of heteroatomic functionalized substituents on PTs recognition sites for self-assembly and chemical sensing... 

The chemical and physical properties of polysilanes are strongly influenced by substituents attached to the polymer backbone. In this respect, heteroatom-substituted polysilanes should be very much intriguing on their properties. However, heteroatom-functional substituents such as amino and alkoxy groups on silicon cannot survive under the vigorous synthetic conditions of polysilanes by the conventional Wurtz-type condensation of dichlorosilanes. Therefore, it is difficult to prepare heteroatom-functional polysilanes. We have recently found that amino-substituted masked disilenes can be prepared and polymerized successfully to unprecedented amino-substituted polysilane of the completely alternative structure, poly[l,l,2-trimethyl-2-(dialkylamino)disilene]. 

Other functional groups that are easily differentiated are cyanide (5c =110-120) from isocyanide (5c = 135- 150), thiocyanate (5c =110-120) from isothiocyanate (5c = 125 - 140), cyanate (5c = 105- 120) from isocyanate (5c = 120- 135) and aliphatic C atoms which are bonded to different heteroatoms or substituents (Table 2.2). Thus ether-methoxy generally appears between 5c = 55 and 62, ester-methoxy at 5c = 52 N-methyl generally lies between 5c = 30 and 45 and. S-methyl at about 5c = 25. However, methyl signals at 5c = 20 may also arise from methyl groups attached to C=X or C=C double bonds, e.g. as in acetyl, C//j-CO-. 

X = heteroatom function L = large substituent S = small substituent... 

In the case of substrates containing OR or related heteroatom functionality, additional coordination complexes and transition states are involved. If a hydroxy group is present, hydride transfer preferably occurs from the corresponding alkoxyaluminate species (i.e., 113) (Scheme 6.68). Substituents of this kind tend to be syn-directing (20-23,140,141,297). 

It is important to note that SNAr displacement reactions of heteroatom functional groups other than halides have been demonstrated on purine substrates, including mesitylenesulfonates <20000L927>, sulfones (see Section 10.11.7.5), nitro substituents <2006S2993>, and T-azoles (see Section 10.11.7.3.2). Halopurines have been reduced using sodium naphthalenide <1997T6295>. 

A series of diaUcylzinc compounds, functionalized with a heteroatom-containing substituent (Scheme 8), has been prepared and was strnctnrally characterized by X-ray crystallographic studies (66" and 69" ) or gas-phase electron diffraction (66, 67", 68 ° and 70"°). The relevant structural data are summarized in Table 4 and, as a representative example, the molecular geometry of 66 is shown in Fignre 33. 

In six-membered rings containing three or more heteroatoms, any substituent must necessarily be close to, or on, a heteroatom. In this respect the reactivity of substituents in these systems is controlled by the adjacent heteroatoms. For example, halogens on carbon atoms or to a heteroatom are readily displaced. For the most part, the reactivity of substituents is fairly easy to predict on the basis of the chemistry of the functional groups of which they are part, and of the generalizations outlined in Chapter 2.02. 

A different mechanism operates in the direct a-heteroatom functionalization of carbonyl compounds when chiral bases such as cinchona alkaloids are used as the catalysts. The mechanism is outlined in Scheme 2.26 for quinine as the chiral catalyst quinine can deprotonate the substrate when the substituents have strong electron-withdrawing groups. This reaction generates a nucleophile in a chiral pocket (see Fig. 2.6), and the electrophile can thus approach only one of the enantiotopic faces. 

In this section, the reactivity of carbon- and heteroatom-containing substituents attached directly or indirectly to the heterocyclic ring of 1,3-dithiole derivatives is discussed. Here, chemical manipulations on these systems exclude ring carbon and sulfur atoms, which are the subject of Section 4.12.6. Special 1,3-dithioles called Jt-extended TTFs, containing two or more 1,3-dithiole moieties linked together via =C-(C=C) -C= or similar conjugated spacers, are discussed with typical TTFs in Section 4.12.11, although formally they constitute an example of functionalization of the 1,3-dithiole by 2rt-extended substituents, terminated by another 1,3-dithiole moiety. 

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