Ligands phosphino-oxazoline

Phosphino-oxazoline)copper complex 28 was found by Helmchen et al. to be an excellent Diels-Alder catalyst [37] (Scheme 1.47, Table 1.20). The nitrogen atom acts as an electron-donating ligand, whereas phosphorus is a cr-donor-Tt-acceptor ligand. The copper complex of this phosphino-oxazoline ligand is therefore expected to have... 

Scheme 9.13 Ru-catalysed reduction of acetophenone with phosphino-oxazoline ligands.

Various phosphino oxazoline ligands were designed, and they can also be optimized via high-throughput catalyst screening for certain applications. In (244), a near square planar environment with two nitrogen atoms in a cis position relative to each other is observed.6 9... 

Chiral chelating ligands that contain only one phosphine and another donor atom have been successful in recent years. A readily synthesized example is the phosphino-oxazoline ligand 87 shown in Scheme 31. These types of ligand can be prepared in two steps from an amino alcohol, a substituted benzonitrile and either a electrophillic or nucleophilic phosphorus reagent. They have been used in a number of asymmetric reactions. 

Selective lithiation of alkyl- or aryl-pyridines is the key to the synthesis of a range of new phosphinopyridine ligands, e.g., (5), (6), and a fused phosphinomethylpyridinoferrocene. A similar approach has been used in the synthesis of chelating phosphino-oxazoline ligands, e.g.,... 

Various q disation reactions have been achieved using enantiomerically pure palladium catalyst through an allyhc substitution process. One of the first reported examples of such a cyclisation, with substrate (10.81), is also one of the most selective reactions, with control of both enantioselectivity and diastereoselec-tivity. Enantioselective cychsation reactions using phosphino-oxazoline ligands have been reported by Pfaltz, although the enantioselectivities (up to 87% ee) are lower than for most intermolecular reactions. ... 

Ogasawara, M., Yoshida, K., Kamei, H. et al. (1998) Synthesis and apphcation of novel chiral phosphino-oxazoline ligands with 1,1 -binaphthyl skeleton. Tetrahedron Asymmetry, 9, 1779-87. 

Liu, D., Dai, Q. and Zhang, X. (2005) A new class of readily available and conformationally rigid phosphino-oxazoline ligands for asymmetric catalysis. Tetrahedron, 61, 6460-71. 

Gilbertson and co-workers prepared phosphino oxazoline ligands with a norbornadiene scaffold (Scheme 2.43). 

In Chapter 2, Section 2.4.4 it is mentioned that Helmchen and co-workers developed series of P-stereogenic phosphino oxazoline ligands (PHOX) with a stereogenic phosphorus atom by either nucleophilic or electrophilic substitutions at the appropriate phosphorus precursors. However, only major dia-stereomers are accessible and the method was not applicable to achiral substrates. To overcome this limitation, their attention was turned to Pd-catalysed phosphination of o-substituted aryl iodides (Scheme 6.26). ... 

Substituted cyclobutanones have been converted to enantioenriched y-lactones by palladium-catalysed BV oxidation, using chiral phosphino-oxazoline ligands, giving yields up to 99% and 81% ee, rising to >93% ee through a single recrystallization. ... 

The use of sulfonates as nucleophiles as a method to form enantiomerically enriched allyl sulfones was first reported by Hiroi and Makino in 1986.Acyclic allyl sulfones have been prepared from substrates 4 and 188 under the control of phosphino-oxazoline ligands 29 (R = Ph) ] or Trost ligand 20. 531 The reaction has also been applied to cyclic substrates including carbonate 191 (Scheme 39).B5 ]... 

An unusual zwitterionic dinuclear Pd(ii) complex 73 was obtained with a phosphino-oxazoline ligand. 

Schemes 58-62. A new non-rigid phosphine ligand was synthesized and reacted with Fe(CO)5 to form the mononuclear iron complex (Equation (81)). Phosphino-oxazoline ligands were used as assembling ligands for hetero-metallic complexes, where the phosphorus atom binds to iron and the nitrogen atoms act as donor atoms to copper, cobalt, or palladium (Scheme 58). The copper complex catalyzes cyclopropanation and Diels-Alder reactions. When 2-(A -diphenylphosphinomethyl-A -cyclohexyl)aminopyridine (NNP) reacts with Fe(CO)5 in ethanol, /ra .r-(OC)3Fe(NNP)2 is formed (Scheme 59). This monometallic complex can then be reacted with a copper salt in CH2GI2 to form a complex having an Fe-Cu dative bond. The complex was demonstrated to be an efficient catalyst for the cyclopropanation of styrene by ethyl diazoacetate and for the Diels-Alder reaction of cyclopentadiene and methacrolein. No other heterometallic complexes have been shown to have such reactivity. Previously known...

An additional feature of P,0- or P,N- chelate keto-phosphine, phosphino-ester, or phosphino-oxazoline ligands is the acidity of the PGH proton which can be easily deprotonated in the presence of a base. This reactivity is nicely shown by... 

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