2,6-Xylylisocyanide

L = THF, OEt2, DME, bipy, PEt3, 2,6-xylylisocyanide, pyrazine. or MejSiCCCCSiMe,)... 

In reaction of trans-PdI(Me)(PPhj)2 with 2,6-xylylisocyanide, complete substitution of the coordinated tertiary phosphine occurs and X-ray diffraction of the reaction product shows one isocyanide group to be terminally bonded to palladium(II), whereas the other three form a five-membered ring of the type suggested for the product of reaction (e). 

Thiophene-cyclopentadienone cooligomers have been similarly prepared from an acetylenic precursor (Scheme 143) <94CC229>. The crucial step is the intramolecular cyclization of a diyne with 2,6-xylylisocyanide. 

The synthesis of indoles from 2,6-xylylisocyanides involving sp C-H bond activation has been reported as early as 1986. The catalyst precursor was the ruthenium (II) complex RuH2(dmpe)2 (dmpe=l,2-dimethylphosphinoethane) and the reaction was performed at 140°C in a sealed tube in the presence of 20 mol% of the catalyst (Scheme 60) [63]. The catalytic reaction could also be carried out in the presence of RuH(2-naphthyl)(dmpe)2 but required the presence of hydrogen to complete the catalytic cycle, which is proposed in Scheme 61 [65, 66]. The catalytic preparation of indoles was only possible starting from 2,6-disubstituted isocyanides (2,6-dimethyl, 2-ethyl-6-methyl, 2,6-diethyl), whereas less substituted isocyanides only led to stoichiometric formation of indole ruthenium species [66]. 

Jones and coworkers described the formation of 7-methyl indoles from ruthenium-catalyzed C(sp )-H bond activation of 2,6-xylylisocyanide in 1986 (Eq. (7.1)) [6]. The catalytic reaction proceeded by using ruthenium(II) complex Ru(dmpe)2H2 or Ru(dmpe)2(2-naphthyl)H as catalyst (20mol%) in CgDg at high temperature (140°C). Further studies indicated that the substrate scope is restricted to 2,6-disubstituted (2,6-dimethyl, 2-ethyl-6-methyl, 2,6-diethyl) isocyanides, since less substituted isocyanides only produced stoichiometric indole N-H oxidative addition adducts with [Ru(dmpe)2]. 

Scheme 7.1 Proposed mechanism for ruthenium-catalyzed indole synthesis from 2,6-xylylisocyanides.

Treatment of the molybdenum alkylidyne complex 191 with 300 atm CO affords a mixture of three products the products of substitution of one and two phosphite ligands and complex 192 [Eq. (154)] (91). The methox-ycarbonyl group in 192 may have arisen from the reaction of an intermediate ketenyl ligand with methanol (derived from hydrolysis of trimethyl-phosphite). Reaction of the compounds 193 with xylylisocyanide was shown to give complexes 194 [Eq. (155)] (91). The products contain the... 

The uncoordinated phosphorus atoms in [Pt2 (/x-dpmp)2L2] (PFe)2 (L = xylylisocyanide) can bind a rhodium atom in... 

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