Isocyanide functional group

In this paper, we describe the synthesis and initial reactivity studies of a macromolecule (Scheme 1) containing the isocyanide functional group [Z = -N=C ] tethered to a polysiloxane backbone. 

A third property that characterizes the reactivity of isocyanides is their a-acidity. Introduction of an electron withdrawing group (EWG) at the a-position of isocyanides considerably lowers the pKa-value of the a-hydrogens. Consequently, a-acidic isocyanides have, besides the aheady unusual reactivity of the isocyanide functional group, an additional nucleophilic center upon proton abstraction. This opens different reaction paths towards a range of interesting products, including heterocycles. 

Figure 8 Sponge terpenoids containing the rare isocyanide, isothiocyanide, and dichloroimine functional groups...

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-. 

TMSlsSiH is an effective reducing agent for the removal of a variety of functional groups, including halides, selenides, xanthates, and isocyanides. 

As indicated above in chiral mesophases, the introduction of a functional group in mesogenic stmctures offers the opportunity to achieve functional LCs. With this aim, mesomorphic crown-ether-isocyanide-gold(I) complexes (26) have been prepared recently [38]. The derivatives with one alkoxy chain show monotropic SmC mesophases at or close to room temperature. In contrast, the complexes with three alkoxy chains behave as monotropic (n = 4) or enantiotropic (n > 4) LCs. The structure of the mesophases could not be fully eluddated because X-ray diffraction studies in the mesophase were unsuccessful and mesophase characterization was made only on the basis of polarized optical microscopy. These complexes are luminescent not only in the solid state and in solution, but also in the mesophase and in the isotropic liquid state at moderate temperatures. The emission spectra of 26a with n=12 were... 

The procedure described here is not limited to the preparation of polymers such as 2. Starting from the difunctional silane 3 we have synthesized a copolymer, poly(dimethyl-co-isocyanopropylmethyl-siloxane) > as well as a linear homopolymer, poly(isocyanopropyl-methylsiloxane) 8 (Scheme 2). Indeed, preparation of a monofunctional analogue of 2. and h creates the potential for end-capping with an isocyanide function any polymer containing other functional groups, thereby in principle permitting mixed ligand complexes of polymers to be accessed. 

In the 1890s, Nef mentioned that the functional group —NC of the isocyanides contains a divalent carbon atom C° and therefore there is a large difference between their chemistry and that of the other chemical compounds that contain only tetravalent carbon atoms Any synthesis of isocyanides corresponds to a conversion of into and all chemical reactions of isocyanides correspond to transitions of the carbon atoms C into... 

The p-functionalized 2-hydroxyphenyl isocyanide not only contains the isocyanide and the nucleophile within the same molecule, but both functional groups are also arranged in one plane for an intramolecular nucleophilic attack [176]. This arrangement, in addition to the aromaticity of the five-membered ring obtained after cyclization to the carbene ligand, particularly favors the intramolecular nucleophilic attack. In contrast to 2-hydroxyethyl isocyanide, free 2-hydroxyphenyl isocyanide is not stable [177]. The stable 2-trimethylsiloxyphenyl isocyanide [178] can serve as a synthon for 2-hydroxyphenyl isocyanide. Carbene complexes 63 with an NH,0-stabilized NHC ligand can be obtained from the complexes 62 with the... 

Since their first isolation (Lieke, 1859 [23]), exceptional reactivity has been observed for isocyanides. For example, their easy formation of radicals and their ability to react both as a nucleophile and as an electrophile at the same atom (a-addition) is unrivaled by other functional groups. Although they are overall in the minority, IMCRs are considered to be more versatile and diverse than other MCRs. 

The structural chemistry of silicon bonded to special functional groups such as acetyl group, cyanide and isocyanide deserves special attention. Acylsilanes having the general formula l SiC.OR constitute an interesting class of chemical compounds. They are sensitive to light and rather unstable, particularly in a basic environment, where they react... 

Tris(trimethylsilyl)silane is found to be an efficient reducing agent for a variety of functional groups. In particular, the reduction of halides, chalcogen groups, thiono esters and isocyanides are the most common ones. The efficiency of these reactions is also supported by available kinetic data. The rate constants for the reaction of (TMS)3Si radicals with a variety of organic substrates are collected in Table 2. 

In general, the hydrolysis of amides requires conditions that are not compatible with the survival of several functional groups [10]. If the amide nitrogen is linked to an electron-withdrawing moiety, alkaline hydrolysis of the amide group is easier. Following this observation Martens and co-workers used 4-methoxy-2-nitrophenyl isocyanide 14 (or 2-methoxy-4-nitrophenyl isocyanide) as a convertible isocyanide for the preparation of Peptide Nucleic Acid (PNA) monomers [8a] (for another example, see Ref. [11]). The Ugi-4CR between isocyanide 14, carboxymethyl nucleo-... 

Most major chemical suppliers maintain hsts of structures sorted by functional groups. Sigma-Aldrich lists approximately 600 aldehydes, 800 amines, 1,400 acids, and 30 isocyanides in its catalog. Of these compounds, 80% of the acids and aldehydes, 25% of the amines, and all the isocyanides are appropriate for the Ugi reaction. How large a library of Ugi products could be formed from the Aldrich building blocks (Ugi, I. The a-Addition... 

---