Insertion isocyanide

Isocyanide is isoelectronic with CO and a reactive compound in the presence of Pd catalysts. The heterobicyclic compound 127 is obtained by the successive insertion of 2.6-xylyl isocyanide (126) into the Pd-hydride bond formed from the hydrosilane[121. Aryl isocyanide inserts into the Si—Si bond in oligo-silanes. For example, 3 mol of 2,6-xylyl isocyanide insert into the tetrasilane 128 to give 129[122],... 

Such titanium sulfinates are reported to increase crop yields (407—409). Isocyanides insert to yield imines as follows (410,411) ... 

Isocyanide insertion and related reactions. Y. Yamamoto and H. Yamazaki, Coord. Chem. Rev., 1972,8,225-239 (47). 

In the reaction of Ni(CNBu )4 and methyl iodide oligomerization of the isocyanide was observed the only isolable nickel complex was (I), shown below. This product is believed to arise through sequential insertions of three isocyanides into a nickel-carbon bond. Upon further treatment with additional isocyanide at a temperature greater than 60° C one obtains a polymer (RNC) presumably through multiple isocyanide insertion reactions. The addition of benzoyl chloride to Ni(CNBu )4 gave two isolable compounds Ni(CNBu )3(COPh)Cl (74%) and (II) (8.2%). This latter reaction, and the isolation of (II) in particular, suggests that the proposed mechanism for polymerization of isocyanides is reasonable. 

The indazoline products can also be made directly from the palladium complexes 78 by heating them with the isonitrile in toluene at 120CC.162 They are also formed in dicobalt octacarbonyl-catalyzed reactions of azo-arenes with isocyanides but in this case an alternative reaction pathway leading to indazolo[2,l- ]indazoles (79) is observed (Scheme 96).163 Products of the latter type are formed from sterically hindered isocyanides hence it is likely that in these cases a double metallation is favored over isocyanide insertion into a monometallated species (Scheme 97). 

Insertion of isocyanides into Si-Si bonds of oligosilanes has been examined. For instance, 2,6-xylyl isocyanide inserts into every Si-Si bond of decamethyltetrasilane in the presence of palladium(n) acetate, whereas the use of a more bulky 2,6-diisopropylphenyl isocyanide leaves the central Si-Si bond intact (Scheme 30).133,134... 

Isocyanides react similarly with ir-allylpalladium complexes to generate P,y-un saturated im-inoethers.240"243 Comparable to the CO reaction, isocyanide insertion occurs preferentially in the less... 

Isocyanide insertion into ir-allylpalladium complexes generally occurs regioselectivity into the less substituted allyl terminus (equation 300).240... 

Facile isocyanide insertion reactions into metal-carbon, -nitrogen, -sulfur, -oxygen, - hydride, and - halide bonds have been found to readily occur. The insertion into metal-hydrides to give stable formimidines is particularly noteworthy since corresponding formyls (—CHO) are exceptionally difficult to synthesize and tend to be very unstable. There is a great deal of interest in carbon monoxide reductions, and the instability of the intermediate reduction products has made a study of the reduction process extremely difficult. Recently, however, the interaction of isocyanides with zirconium hydrides has allowed the isolation of the individual reduction steps of the isocyanide which has provided a model study for carbon monoxide reduction (39). 

Although reaction of organozirconocene compounds fails with most organic electrophiles, treatment with sterically unhindered isocyanides, such as rcBuNC, is possible." Organometallic species 24 attacks nBuNC 25 to give isocyanide-insertion product 26, which is finally hydrolyzed to the one-carbon homologated aldehyde 6. 

The structurally novel antimitotic agent curacin A (1) was prepared with an overall yield of 2.5 % for the longest linear synthesis. Three of the four stereogenic centers were built up using asymmetric transformations one was derived from a chiral pool substrate. Key steps of the total synthesis are a hydrozirconation - transmetalation protocol, the stereoselective formation of the acyclic triene segment via enol triflate chemistry and another hydrozirconation followed by an isocyanide insertion. For the preparation of the heterocyclic moiety of curacin A (1) the oxazoline - thiazoline conversion provides efficient access to the sensitive marine natural product. 

Scheme 10. Formation of a Sc-N

A zirconaaziridine can also result from the thermal rearrangement of an imi-noacyl hydride complex, formed by isocyanide insertion into one Zr-H bond of a dihydride. Bercaw and coworkers observed (Eq. 8) that ArNC insertion into a Zr-H bond of Cp5ZrH2, followed by hydride transfer to the iminoacyl ligand of 9, formed the zirconaaziridine 10, although 10 rearranged upon further thermolysis [35]. 

Scheme 1 Formation and trapping of zirconaaziridine after isocyanide insertion into Zr-R...

Products of type (21-XXX) are quite common for isocyanide insertions (see later). 

Examples of multiple isocyanide insertions into Pd—C,173 Pd—H,174 and even Pd-S,175 bonds are compounds (21-XXXVI) - (21-XXXVIII) ... 

The mechanism of the isocyanide insertion has been examined for the coordinatively unsaturated platinum(II) alkyls and aryls 127) it involves an ionic intermediate in which both R NC and R are coordinated to the metal [Eq. (40)]. Coordinatively saturated alkyl complexes are believed... 

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