Phosphine-based copper reactions

Table 5.2 Intramolecular epoxIde-openIng reactions of epoxy aryl halides using phosphine-based active copper.

The coupling of secondary phosphines with aryl iodides was also extended to pyridines. 3-Iodopyridine and diphenylphosphine were coupled to give 3-diphenylphosphino-pyridine in 60% yield (7.80.), The catalyst in this reaction consisted of copper(I) iodide and N,N -dimethylethylenediamine and caesium carbonate was used again as base.102... 

Reactions of limited proportions of amine and phosphine Lewis bases with non-molecular copper and silver halides generate crystalline cubanes. Crystallographic determinations of molecular structure have been reported for at least 31 complexes with cf or d10 metal configurations, spanning the following types or homologous series of compounds. Compilations of data occur in references 157, 158 and 167. 

Bromothiophene has been coupled with phenylacetylene in a copper-free reaction to give a 96% yield of the product (Equation 33) <20030L4191>. A Pd(ll) complex containing the ferrocene-based phosphinimine-phosphine ligand 83 has proved very efficient for the reaction of 2-iodo- and 2-bromothiophene with phenylacetylene the coupling takes place under copper- and amine-free conditions (Equation 34) <2004TL4337>. 

Binaphthol-based phosphorus amidite 30 was developed by Feringa to afford 3-ethylcyclohexanone in over 98% ee [64, 65]. However, high enantioselectivity is limited to cyclohexenone, and rather poor selectivity was observed in the reaction of cyclopentenone (10% ee) and cycloheptenone (53% ee). Symmetric aminophosphine ligand 31 was synthesized and the reaction with cyclohexenone was examined in the presence of 5 mol% of copper triflate to afford the product in 55% ee [66]. Amide-phosphine 32 was examined in the reaction to afford the product in 35% ee. Higher selectivity (64%) was observed in the reaction of 4,4-dimethylcyclohexenone [67, 68]. 

Since the bisphosphine or monophosphine greatly accelerates the copper-catalyzed reaction [58], a survey of the known diphosphines was carried out and revealed that 0.5% of copper(II) triflate and 0.5% of phosphine are sufficient, although enantioselectivity was at the most 44% [59]. The chiral phosphite hgand based on tartrate 22 (Scheme 14) was also observed to exert the same hgand acceleration [60],but the ee was not so satisfactory [61]. 

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