Phosphite-phosphoramidite

The use of phosphite-phosphoramidite ligands 168 a and b provided up to 98% ee in the hydrogenation of methyl (Z)-N-2-acelylarrii noci rinamale, but the activities were rather low when compared to 167 or to the corresponding diphosphine ligand [126]. 

It was later found that dialkyl(dialkylamino) phosphites (phosphoramidites, (RO)2PNR2 [114]), which are stable towards air and water and can be stored for longer, can readily be converted into the phosphinic chlorides (RO)2PCl by treatment with dimethylaniline hydrochloride, or into the corresponding tetrazolides by treatment with tetrazole. Tetrazolides (RO)2P-(l-tetrazolyl) had proven excellent reagents for the phosphorylation of nucleosides [113], and the treatment of phosphoramidites with alcohols in the presence of tetrazole was found to be a satisfactory method for the rapid preparation of trialkyl phosphites [115,116]. 

DIAD) with cyclic phosphites/phosphoramidites were examined in an effort to delineate the structural preferences in spirocyclic penta- and tri- cyclic hexacoordi-nate (amino)oxyphosphoranes. Thus the reaction of (38) with DEAD or DIAD leads to the chlorophosphoranes (39). Treatment of (39) with pyrazole or imidazole leads to (40) that have trigonal bipyramidal phosphorus with reversed apicophili-city . Compound (41, Y = NH/Pr) and DIAD affords the pentacoordinate... 

In comparison to other ligands, such as phosphines or phosphites, phosphoramidites represent quite a new class used in hydroformylation. With the exception of carbenes, which were introduced as the most recent class of ligands in 1997 (see Section 2.5), the first successful attempts with phosphoramidites were made in 1996 [3]. As with phosphites, the first phosphoramidites (in particular A/ -pyrrolylamidites) were designed for use as flame retardants [4]. 

Figure 2.38 Chiral bidentate phosphite-phosphoramidite ligands based on carbohydrates.

Scheme 7.6 Alkylations of aromatic aldehydes with AIR3 and (AlR3)2-DABCO in the presence of an in situ generated nickel catalyst from a D-glucose-de-rived phosphite-phosphoramidite ligand.

The group of Alexakis subsequently reported a study on the use of bidentate furanoside phosphite-phosphoramidite and diphosphoramidite ligands for the Cu-catalysed AAA of cinnamyl-type substrates [29]. A range of different cinnamyl... 

Suitable methods for linking a phosphoms—nitrogen bond to the ayiridine ring are the aminolysis of halogenated phosphoms compounds (2,280—282), the transamination of phosphoramines with excess a iridine (283), the reaction with phosphites (284) and phosphoramidites (285) which have a free OH group, or the reaction of phosphines with a iridines and carbon tetrachloride (286). 

The disadvantage of this method is that the dichloridites and monochloridites are sensitive to water and thus could not be used readily in automated oligonucleotide synthesis. This problem was overcome by Beaucage and Caruthers, who developed the phosphoramidite approach. In this method, derivatives of the form R 0P(NR2)2 react with one equivalent of an alcohol (catalyzed by species such as l//-tetrazole) to form diesters, R OP(OR")NR2, which usually are stable, easily handled solids. These phosphoroamidites are easily converted to phosphite triesters by reaction with a second alcohol (catalyzed by l//-tetrazole). Here, again, oxidation of the phosphite triester with aqueous iodine affords the phosphate triester. Over the years, numerous protective groups and amines have been examined for use in this approach. Much of the work has been reviewed. ... 

Phosphine(s), chirality of, 314 Phosphite, DNA synthesis and, 1115 oxidation of, 1116 Phospholipid, 1066-1067 classification of, 1066 Phosphopantetheine, coenzyme A from. 817 structure of, 1127 Phosphoramidite, DNA synthesis and, 1115 Phosphoranc, 720 Phosphoric acid, pKa of, 51 Phosphoric acid anhydride, 1127 Phosphorus, hybridization of, 20 Phosphorus oxychloride, alcohol dehydration with. 620-622 Phosphorus tribromide, reaction with alcohols. 344. 618 Photochemical reaction, 1181 Photolithography, 505-506 resists for, 505-506 Photon, 419 energy- of. 420 Photosynthesis, 973-974 Phthalic acid, structure of, 753 Phthalimide, Gabriel amine synthesis and, 929... 

An extensive paper by Burgada et l. reports the reactions of cyclic phosphites (75 ab) and cyclic phosphoramidites (76 ab) with trans-1,2-dibenzoylethene, methyl fumarate, benzalacetone (PhCH=CH COMe), methyl-4-keto-pent-2-enoate (MeCO.CH=CH.COgMe) and benzalacetophenone (PhCH=CHCOPh)95. These reactions lead to... 

A new structural feature is obtained by replacement of the phosphite donor within BINAPHOS by a phosphoramidite system. Improved enan-tioselectivities were noted, albeit the problem of regioselectivity persists (Scheme 20) [69]. 

A variety of substrates has been used in this type of conjugate addition reaction with trialkyl phosphites, with assorted proton sources.361 384 Other types of trivalent phosphorus reagents without acidic (or conjugate base of acidic) sites have also been used successfully for this conjugate addition process, including triaryl phosphites (without dealkylation),369 phosphoramidites,385 389 phospho-nites,363 380 390 and phosphinites.360 380... 

A remarkable number of chiral phosphorus ligands (phosphoramidites, phosphites, and phosphines with modular structures) have been introduced into the copper-catalyzed conjugate addition of R2Zn reagents, and high enantio-selectivities (>90%) are now possible for all three different classes of substrates 2-cyclohexenones and larger ring enones, 2-cyclopentenones, and acyclic enones. 

The use of monodentate phosphoramidites in enantioselective hydrogenation was first reported in 2000, together with reports on the use of phosphites and phospho-nites [15]. Phosphoramidites are prepared in a variety of ways, but the most common route is the treatment of a diol with PC13, followed by addition of an amine [60, 61]. MonoPhos (29a), the first reported phosphoramidite used as a ligand, is prepared from BINOL and HMPT in toluene [62]. Phosphoramidites, especially... 

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