Copper-Isonitrile complexes

Review Synthesis of cyclic compounds via copper-isonitrile complexes. 

The isolation of cyclopentanecarboxylates from 1,3-diiodopropane and an acrylate in the presence of metallic copper and an alkyl isonitrile has been reported by Saegusa and coworkers (equation 39). The reaction is proposed to involve formation of a transient 3-iodopropylcopper-isonitrile complex (47) from the diiodopropane, which then adds to the unsaturated ester in a Michael fashion (equation 40). The nonconcertedness of this reaction results in stereoselective cycloaddition. For example, Iratfa diethyl ma-leate and fumarate produce the same cyclopentane adduct in identical yields (equation 41). The generality of this cycloaddition has not been explored. 

Under N, 1.48 g (5 mmol) of 1,3-diiodopropane in 4 tnL of toluene are added dropwise with stirring over 30 min to a preheated mixture of 1.27 g (20 mmol) of metallic copper. 4.40 g (40 mmol) of cyclohexyl isoevanide. 1.72 g (10 mmol) of diethyl fumarate and 6 mL of toluene at 110 CC. The reaction mixture is heated for 12 h at 110 C and is then treated with Et,<) to remove the copper iodidc/isonitrile complex. The extract is concentrated and distilled in vacuo yield 0.82g (90%) by preparative GC. 

Schreiber and co-workers have described the use of a copper(II) complex with an aminoindanol-derived pyBOX ligand for the catalytic enantioselective addition of isonitriles to bidentate aldehydes to give a-acyloxyamides such as 38. Excellent yield and good enantioselectivity is observed in many cases and the protocol was also applied toward tandem Passerini-intramolecular Diels-Alder reactions for use in complexitygenerating diversity oriented synthesis. 

Imidazoles carrying a long alkyl chain as a ligand for the copper(I)-catalyzed azide-alkyne cycloaddition are also very efficient. An alkyl chain can readily change its conformation in a host molecule to adjust its volume to the cavity size and may have an appreciable steric effect [15]. The copper(I) isonitrile complex prepared upon treatment of isonitriles with CuCl in THF in 95% yield as [CuLCl] units extended in a polymeric chain is stable in air or water for several months. This complex catalyzes the reaction of azides and acetylenes in water at room temperature in 0.5-5 mol% loading to give excellent yields in very short times. The catalyst may be recycled through five cycles [16-18]. 

The tetrameric o-(dimethylaminomethyl)phenylcopper, which is similar to (III) and probably possesses the same structural features, forms monomeric complexes with l,2-bis(diphenylphosphino)ethane and -ethylene but not with triphenylphosphine (281e). Insertion of an isonitrile into the aryl—Cu bond occurs rather than formation of a complex (281d). The new copper compound is dimeric in benzene, and a six-membered ring structure involving heteroatom coordination bonding as in (V) is proposed. Triphenylphosphine breaks down the dimer (V)... 

Selenol esters also reacted with isonitrile (44 Scheme 13) at room temperature for 6-20 h in the presence of 1.5 equiv. of copper(I) oxide and triethylamine (or DBU) to give oxazole (45). The reaction presumably proceeds through an intermediate 3-ketoisonitrile (46), and copper(I) oxide functions as a reagent for complexation to the selenium moiety. 

Synthesis of cyclic compounds. Review. Metallic copper also forms complexes with isonitriles, which have been used for the synthesis of cyclopropanes, as formulated in equations I and II. The reaction has been extended to a syn-... 

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