Pd-Catalysed Arylation of Silylphosphines

The enantioselectivity was optimised for the coupling of w-iodoanisole with silylphosphine 62. The best conditions were 5% of Et-FerroTANE catalyst in 

Af -dimethylpropylene urea (DMPU) as solvent. After borane protection, 63 (Ar = w-anisole, X = BH3) was obtained in 91% yield and 56% ee. Then, following the work of Helmchen and co-workers (see previous section), the attention was turned to o-iodoarenes (Table 6.9). 

Silylphosphine 64 containing an electron-poor difluorophenyl group causes a dramatic decrease in the enantioselectivity (entry 1), in contrast to changes in the alkyl group which are well tolerated (entries 2-4). 

Complex 66 is supposed to be present as a mixture of two diastereomers (epimers). Rapid interconversion between them relative to reductive elimination enables the dynamic kinetic resolution to take place. The striking performance of 2-iodo-A,A-diisopropylbenzamides was not mechanistically investigated but coordination of the amide carbonyl group to the Pd centre, forming a five-membered palladacycle, was suggested. 

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Table 6.9 Results of Pd-catalysed arylation of silylphosphines with o-iodoarenes (Scheme 6.28).

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