Phosphoramidite styrene

At present, phosphoramidites represent the most promising ligand class for the hydrovinylation reaction, both for the excellent activities and enanioselectivities. The synthetic potential embraces not only styrene and styrene derivatives but also norbornene [54] and 1,3-dienes [55]. 

The synthesis of a nucleotide-like phosphoramidite building block in which the nucleic base has been replaced by a tert-butyldimethylsilyl-protected styrene glycol (47) has been described. After its incorporation in an oligonucleotide by automated synthesis, the terminal alcohol has been oxidized with NaI04 after fluoride deprotection. A similar phosphoramidate in which the nucleic base has been replaced by an alkyl diol (48) has been incorporated in an oligonucleotide and further conjugated with biotin after oxidation to the aldehydic functional-ity. ... 

Hydrovinylation. Addition of ethylene to styrenes occurs in the presence of the Ni-complex of phosphoramidites. Tuning of the catalysts indicates the unsymmetrical aminophosphite 5 is a good performer for asymmetric induction. 

Johannsen and co-workers found that the phosphoramidite of axially chiral BINOL (IH-9) is an effective chiral ligand, and they obtained 32 with 99 % ee in 87 % yield from styrene. Also they prepared 1-trichlorosilyl-l-phenylpropane (35) with 98 % ee in 91 % yield by the hydrosilylation of /S-methylstyrene (34) with this ligand, and chiral 1-phenyl-1-propanol was prepared from 35 [21]. Furthermore, they claimed that arylmonophosphinoferrocene was an efficient ligand. In particular, the p-MeO-Ph-MOPF (VIII-8) they synthesized was the most effective ligand for asymmetric hydrosilylation of styrene, and ultrafast asymmetric hydrosilylation occurred with TOF exceeding 180000 h [22]. 

In 2009, P-chiral phosphorus triamide ligands were applied in Ni-catalyzed asymmetric hydrovinylation of styrene with promising results, good yields (77%), and good enantioselectivity (up to 63% ee). Recently, phosphoramidite and P-stereogenic phosphorodiamidite ligands L17 and L18 derived from (Sj-2-phenylamino-2 -hydroxy-l,l -binaphthyl (7y-Ph-NOBIN) and bis(l-phenyl-ethyl)amine were synthesized and applied in asymmetric hydrovinylation of styrene, leading to almost perfect selectivity and enantioselectivity (up to 91% ee) (Scheme 9.5). ... 

Scheme 9.4 chiral phosphoramidite ligands used in hydrovinylation of styrenes. 

In 2005, the Zhou group applied the biindane-derived ehiral spiro phosphoramidite and phosphite ligands in the Pd-catalyzed asymmetric hydrovinylation of styrene. However, only moderate yield and enantiose-lectivity could be obtained. Recently, Muller and co-workers synthesized Cj-symmetric tris-binaphthyl monophosphite ligand L29, and used it in the Pd-catalyzed asymmetric hydrovinylation reaction. The hydrovinylation product of styrene could be obtained in 70% conversion and 92% ee (Scheme 9.12). ... 

In addition to the extensive studies of hydrovinylations using styrene substrates, 1,3-dienes are also an especially useful substrate class. With phosphoramidite ligands, enantioselective diene hydrovinylation with ethylene provides a practical solution to the difficulties associated with the installation of exocyclic side chain stereochemistry, as the representative procedure below illustrates. ... 

Wassenaar and Reek [28] prepared four chiral phosphine-phosphoramidite ligands called INDOLPhos and tested them in the hydroformylation of styrene (Scheme 2.129). In the best case, a b/l ratio of 10 and enantioselectivity of 72% were observed. 

Phosphine-phosphoramidites also make up the core region of some supramolecular bimetaUic catalysts [31]. These compounds have been intensively investigated for asymmetric hydroformylation of styrene, where a significant influence on activity and selectivity has been attributed to the Zn(II) template. 

In 2007, Leitner et al. reported the synthesis of novel monodentate Quina-phos phosphoramidites bearing different substituents in the 2-position of the 1,2-dihydroquinoline backbone. These ligands were further investigated in the enantioselective nickel-catalysed hydrovinylation of styrene in the presence of NaBArF. Among them, Cl-Quinaphos phosphoramidite bearing an n-butyl substituent in the 2-position of the 1,2-dihydroquinoline backbone, was demonstrated as optimal, providing the corresponding 3-phenylbut-l-ene in enantioselectivity of 91% ee and almost quantitative yield, as shown in Scheme 5.4. 

Scheme 5.5 Hydrovinylation of styrene with a preformed phosphoramidite chiral nickel catalyst activated by Inlj.

New chiral phosphoramidites were synthesised from chiral un-symmetrical amines and BINOL. The ligands were subsequently applied to the enantioselective hydrosilylation of styrenes.In addition, reports of... 

The asymmetric hydrosilylation was studied for styrene and substituted styrene derivatives. The use of 1 associated with a monodentate phosphane ligands afforded, after oxidative cleavage, the corresponding alcohol with various enantiomeric excesses (eq 91)P The best results were obtained with (5)-H-MOP and a phosphoramidite ligand. 

The CuBr2/amine-promoted 2 + 2-cycloaddition reaction of 1,4-bisallenes (17) produced bicyclo[4.2.0]octadiene derivatives (18) in a one-pot procedure (Scheme 7) Phosphoramidite ligands (19) activate the Au(I)-catalysed 2 + 2-cycloaddition reaction of A-allenylsulfonamides with styrenes, at -70 C, to form vinyl cyclobutane derivatives in high yields and enantioselectivity. A new Pt(II) catalyst with a hollow-shaped tri- ethynylphosphine activates the intermolecular 2 + 2-cycloaddition reaction of allenyl silyl ether with vinyl ethers to yield methylenecyclobutanes in good yield. 

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