Isocyanide and alkyl

An attractive synthesis of cyclobutanone (253) has been recently described using 1-isocyano-l-tosylcyclobutane(252)(equation 151)144. l-Isocyano-l-tosylcyclobutanes252 can be prepared from (tosylmethyl)isocyanide and alkyl-substituted 1,3-dibromobutanes. This method appears to be superior to previously reported methods for the preparation of cyclobutanone because of high purity and high yields. 

Addition of disilanes to isocyanides is catalyzed by palladium complexes, giving A-substituted bis(silyl)imino-methanes (Equation (53)).132 A wide range of isocyanides including aryl isocyanides and alkyl isocyanides can take part in the reaction. However, it is important to note that tert-alkyl isocyanides hardly undergo the bis-silylation reaction. This low reactivity of / r/-alkyl isocyanides allows their use as spectator ligands in the catalytic bis-silylations. 

Any adequate theoretical treatment must also explain how iron-porphyrin systems can bind not only O2, but also CO, NO, alkyl isocyanides, and alkyl-nitroso moieties. A simple qualitative model presented by Wayland and coworkersconveniently summarizes ligand-binding geometries of cobalt and iron porphyrins. Although a reasonable quantitative theoretical consensus exists for 1 1 cobalt-dioxygen species, the same cannot be said yet for iron-dioxygen systems. 

Another method used to remove phosgene substitutes from the desired products is to destroy them with appropriate nucleophiles such as water or alcohols. This method can, of course, only be applied when the product is insensitive to these nucleophiles, as is the case for carbamates, carbonates, ureas, cyanides, isocyanides, and alkyl chlorides. Chloroformates, carbamoyl chlorides, isocyanates, acyl chlorides, N-carboxylic anhydrides, and carbodiimides, on the other hand, cannot be purified by this method. Consequently, a synthesis of these compounds using phosgene is worthy of consideration. 

Liquid crystals based on aliphatic isocyanides and aromatic alkynyls (compounds 16) show enantiotropic nematic phases between 110 and 160 °C. Important reductions in the transition temperatures, mainly in clearing points (<100 °C), areobtained when a branched octyl isocyanide is used. The nematic phase stability is also reduced and the complexes are thermally more stable than derivatives of aliphatic alkynes. Other structural variations such as the introduction of a lateral chlorine atom on one ring of the phenyl benzoate moiety or the use of a branched terminal alkyl chain produce a decrease of the transition temperatures enhancing the formation of enantiotropic nematic phases without decomposition. 

Detailed procedures for the synthesis of various often used [Ni°L4] complexes (L = phosphines, arsines, stibines, alkyl isocyanides) and [Ni°L 2] complexes (L = bipyridine, phenantroline, diphosphines, diarsines) have been compiled.2413... 

Robertson, M.). and Angelid, R.J. (1994) Adsorption of aryl and alkyl isocyanides on powdered gold. Langmuir, 10,... 

Low oxidation states are generally stabilized by ligands which have both a donor (lone pairs) and n acceptor (either empty d orbitals or empty antibonding Jt orbitals) capability. Examples of common ligands with these characteristics are carbon monoxide, cyanide ion, alkyl and aryl isocyanides, tertiary phosphines and arsines, and alkyl or aryl phosphites. 

The generally accepted valence bond and molecular orbital (MO) approach to the bonding of metal isocyanides has been well described in Treichel s review (6), and has been used to rationalize (i) variations in IR stretching frequencies between bonded and nonbonded isocyanides, and (ii) the better Tt-acceptor qualities of aryl versus alkyl isocyanide groups (53,54). In valence bond theory the canonical forms involved in metal isocyanide bonds are... 

Though alkylation of metal cyanides is one of the oldest routes to metal-isocyanide complexes, at the present time the usefulness of this method is confined to (i) partially characterizing new metal-cyanide complexes, (ii) providing access to complexes containing unstable or unusual isocyanide ligands which cannot be prepared by direct interactions of complex with isocyanide, and (iii) providing a route to chiral metal-isocyanide complexes. The following examples exemplify this. 

An example in which primary alkylamines are used as alkyl radical precursors for cyclization is reported in equation 5061, in which the initial transformation to isocyanide and subsequent reaction with (TMS SiH gave the desired products in 78% yield after workup. 

Isocyanides, Isocyanates, RN=C=0, and alkyl carbamates, R NHCOOR2, are reduced to isocyanides, RN=C, by treatment with trichlorosilane and triethylam-ine in OH, Cl, in yields of 4(l 70%. r-Butyldiphenylsilyllithium2 also effects reduction of isocyanates to isocyanides, but this reagent is less convenient to use. 

The Ugi group has designed a new class of convertible isocyanides, namely alkyl 2-isocyano-2-methylpropyl carbonates [7], prepared from commercially available 4,4-dimethyl-2-oxazoline. The Ugi-4CR of 11 afforded the expected products 12, which were converted into N-acyl a-amino acid esters 13 and N-acyl a-amino acids by in situ hydrolysis (Scheme 2.5) [7]. 

The Passerini reaction between a-chloroketones, isocyanides, and carboxylic acids afforded a-acyloxy-jS-chlorocarboxamides 52, which, on treatment with an excess of powdered KOH in tetrahydrofuran, underwent O-deacylation followed by a Darzens-type O-alkylation to give the functionalized oxiranes 53. When carboxamides 52 were treated with an excess of CsF, with or without a phase-transfer catalyst, a different ring closure took place to afford 3-acyloxy-2-azetidinones 54 in high yields (Scheme 2.21) [46]. 

A less common approach to 2,5-diketopiperazine was reported by Marcaccini et al. [79] who used a Ugi-4CR between amines, aldehydes, isocyanides, and chloroacetic acid to get adducts 140. Treatment of 140 with ethanolic potassium hydroxide led to an intramolecular amide N-alkylation reaction, giving 2,5-diketopiperazines 141... 

The Passerini-3CR between bifunctional 6-oxo-4-thiacarboxylic acids and alkyl-isocyanides, in the presence of a catalytic amount of tributylamine, afforded the tetracyclic structure 171, which included the 1,4-benzothioxepin group and an unexpected oxazolidinone ring, with formation of a rare orthoamide group (Scheme 2.62) [94]. 

Fig. 32. Effects of alkyl isocyanides (a-series) on the 600-MHz ring-current-shifted proton resonances of isolated a chains and (3 chains of Hb A, Hb A, and sperm whale myoglobin (Mb) in 0.2 M phosphate in D20 at pH 6.6 and 21°C MNC, methyl isocyanide ENC, ethyl isocyanide iPNC, isopropyl isocyanide and tBNC, tert-butyl isocyanide. [Adapted from Mims et al. (1983a)].

If correct, this would be an unusual phenomenon because all available evidence indicates that C-coordinated cyanides are generally far more stable than their N-coordinated isomers. For example, aryl and alkyl isocyanides are known but they are thermodynamically unstable relative to their nitriles. 

Cyanide, Alkyl Isocyanide and Aryl Isocyanide Complexes 128... 

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