Phosphorus amidites

Figure 1.12. Phosphorus amidites, phopshorus pyrroles, and phospholes...

The use of vinyl epoxides as substrates in enantioselective copper-catalyzed reactions, on the other hand, has met with more success. An interesting chiral ligand effect on Cu(OTf)2-catalyzed reactions between cyclic vinyloxiranes and dialkylzinc reagents was noted by Feringa et al. [51]. The 2,2 -binaphthyl phosphorus amidite ligands 32 and 43 (Fig. 8.5), which have been successfully used in copper-catalyzed enantioselective conjugate additions to enones [37], allowed kinetic resolution of racemic cyclic vinyloxiranes (Scheme 8.26). 

Deuterium labelling can, in principle, provide mechanistic information on hydro-formylation reactions, but complications may arise if scrambling of the D-label bet veen a metal hydride and D2 is fast. The isotopic exchange reaction shown in Eq. (9) was probed by rapid scan HP IR spectroscopy (1.3 scans s" ) where 21 is the bidentate pyrrolyl-based phosphorus amidite ligand illustrated [8]. 

Oligonucleotide functionalization through phosphorus amidite derivatives 93T1925. 

Recently, copper-catalyzed enantioselective addition reactions in the presence of phosphorus amidite 258 have also been applied to different Michael acceptors. Thus, both symmetrical and unsymmetrical 4,4-disubstituted cyclohexa-2,5-dienones 261 were found to add diethylzinc with moderate to high enantioselectivities and good... 

Progress with regard to this undesired substrate specificity was achieved with the phosphorus amidite 10, which catalyzes not only Michael additions of organozinc reagents to cyclic enones but also to chalcone (11 R = Ph) and related acyclic substrates. In the case of the addition of diethylzinc to chalcone, a good enantioselectiv-ity of 87 % ee was observed [8]. 

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]. 

Many metal-catalysed allylic substitution reactions have been reported. Adding a terminal olefin to the binaphthyl backbone of a phosphorus amidite ligand in a [PdCl(C3H5)]2-ligand-K2C03 catalysed reaction between indoles and l,3-diphenyl-2-propenyl acetate has enabled the allylic substitution to occur, with yields ranging from 72 to 96%, with 91-98% ee. 

Bartel, B., Garcia-Yebra, C., Helmchen, G. Asyimnetric Irl-catalyzed allyUc alkylation of monosubstituted allylic acetates with phosphorus amidites as hgands. Ear. J. Org. Chem. 2003, (6), 1097-1103. 

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