Isonitriles insertion

Interestingly, by using an alcohol (S.Oequiv.yBu ONa (1.2 equiv.) instead of an alkoxide (5.0 equiv.), double isonitrile insertion takes place to give a-iminoimidates (Equation (120)).479... 

Usually, an isonitrile can be inserted without transmetalation. As shown in Eq. 2.67, Majoral et al. have isolated and characterized by X-ray analysis the intermediate involved in isonitrile insertion into zirconaindene complexes [47]. 

The synthesis of analogous iminoacyl complexes by isonitrile insertion into linear alkyl-zirconocene chlorides is also known. In an overall regiospecific hydrocyanation of alkenes, iminoacyls 21 derived from tBuNC or Me3SiCN (as the Me3SiNC isomer) may be treated with I2 to rapidly generate an imidoyl iodide and subsequently the nitrile 22 (Scheme 3.6) [22], Less hindered iminoacyl complexes (e. g. R = Bu, Cy) may be hydrolyzed to afford aldehydes 23 [23]. 

Isonitrile insertion into zirconacycles to afford iminoacyl complexes 28 is fast, but rearrangement to q2-imine complexes 30 is slow. In the case of tBuNC, the rearrangement does not occur. Amines 32 are formed on protonolysis of the q2-imine complex. The q2-imine complexes 30 readily undergo insertion of Ti-components (alkenes, alkynes, ketones, aldehydes, imines, isocyanates) to provide a wide variety of products 37 via zirconacycles 36. The overall sequence gives a nice demonstration of how a number of compo-... 

Scheme 3.7. Carbonylation and isonitrile insertion into zirconacycles.

Methylenezirconacyclobutane complex 99 undergoes double isonitrile insertion, but not reductive carbon-carbon bond formation, yielding the bis(iminoacyl) complex 100 (Scheme 16) <1994AGE2465>. Single insertion is observed using ftTf-butylisocyanate or methyl formate. 

Elimination reactions are typically found in transition metal chemistry. The conversion of allylic ethers into allylzirconocenes [18] is a well-known zirconium-mediated process of this type. In contrast, the y-elimination reactions are less frequently encountered, and only a few examples of y-elimination involving zirconocenes have been reported. When studying isonitrile insertion into zirconacycles, Whitby and coworkers observed an interesting reaction leading to a cyclopropane derivative [19]. The overall transformation is depicted in Scheme 12. Treatment of the diene 18 with preformed butene-zirconocene gave... 

A method for the hydrocyanation of alkenes and alkynes is based upon hydrozirconation followed by isonitrile insertion (Scheme 13) overall yields range from 45-90%. Certain examples do not exhibit the clean regiochemistry represented here, and these were discussed in Section 3.9.3.3.2. The hydrozirco-nation/protonolysis of equation (53) results in high yield, stereoselective formation of C-methyldeoxy-sugars, an alternative to free radical deoxygenation. ... 

Isonitriles insert into the Cu-C bond of arylcoppers. These reactions, which afford new Cu-carbon bonds, proceed quantitatively at RT ... 

The same photocatalyst system permits the observation of the insertion of alkynes into C-H bonds [98]. Isonitrile insertion into aromatic C-H bonds with (C5Me5)Rh(CNCH2CMe3)2 gives aldimines in low yield [99]. Photoinduced... 

The product distribution depends on the isocyanide used. Only with aromatic (R = o-tolyl or 2,6-xylyl), and not with aliphatic isocyanides (R = Bu , Bu or benzyl) are isonitrile insertion products 24 formed. Aryl isocyanide insertion is obviously very fast since the competing formation of 23 from CO insertion is not observed complexes 22 are only minor products. With aliphatic isocyanides, the thpp complexes 22, from double cycloaddition of dmad cf. Section 3.1.1), are the major products (70 to >95% of the product mixture) and indicate a strongly increased 1,3-dipolar reactivity, i.e. the intermolecular second cycloaddition is preferred to the intramolecular CO insertion. Compared with the ruthenium compound 17, the thpp in 22 is strongly bound to the metal and can only be decomplexed oxidatively with cerium(iv), or under 80 bar of CO. 

The reaction of 25a-c with dmad proceeds in a manner completely analogous to the reaction of 21, i.e. giving thpp complexes by double cycloaddition in case of the aliphatic isonitriles (b, c), and isonitrile insertion with the aromatic... 

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