Solvent-Switchable Remote C-H Activation via 1,4-Palladium Migration Enables Site-Selective C-P Bond Formation: A Tool for the Synthesis of P-Chiral Phosphinyl Imidazoles

Solvent-switchable and site-selective phosphorylation of imidazoles at the C2 or C5 position of the imidazole ring was achieved via 1,4-palladium migration. P-Chiral tert-butyl(aryl)phosphine oxides were cross-coupled to 1-(2-bromophenyl)-1H-imidazoles with high enantiospecificity, thereby leading to a novel class of chiral imidazole-based phosphine oxides. As proof of concept, reduction of an analogue yielded the corresponding P-chiral 2-phosphinyl imidazole ligand, which was shown to induce high enantioselectivity in the formation of axially chiral molecules synthesized via Pd-catalyzed Suzuki-Miyaura cross-coupling.

Nucleophilic Substitution of P-Stereogenic Chlorophosphines: Mechanism, Stereochemistry, and Stereoselective Conversions of Diastereomeric Secondary Phosphine Oxides to Tertiary Phosphines

A diastereomeric mixture of secondary phosphine oxide is stereospecifically converted to chlorophosphine salt by treatment with oxalyl chloride, which stereoselectively affords P-inverted or retained tertiary phosphines, depending on the substitution with aliphatic or aromatic Grignard reagents, respectively, in high to 99% yield and 99:1 dr. The repulsion of π-electron on aryl to lone electron pair on phosphorus is proposed for the P-retained substitution.

Applications and stereoselective syntheses of P-chirogenic phosphorus compounds

This review reports the best stereoselective or asymmetric syntheses, the most efficient P*-building blocks and functionalisation of P-chirogenic compounds, in the light of chiral phosphorus compound applications.

Enantiomerically pure P-chiral phosphinoselenoic chlorides: inversion of configuration at the P-chirogenic center in the synthesis and reaction of these substances

Reaction of diastereomerically pure phosphinoselenoic acid salts with oxalyl chloride leads to enantiomerically pure P-chiral phosphinoselenoic chlorides with inversion of configuration at phosphorus; one of these chlorides is converted to a phosphinoselenothioic acid salt with a high degree of enantioselectivity.

Synthesis of phosphorofluoridates and phosphorofluoridothioates via the phosphoramidite approach

We present a very efficient synthetic procedure leading to the phosphorofluoridates RO-P(O)(OH)F 1 or phosphorofluoridothioates RO-P(S)(OH)F 2, which is based on the intermediary of fluorophosphoramidites (RO)P(F)N(i)Pr2 5 [R = 9-(hydroxyethyloxymethyl)guaninyl), 3'azido-3'deoxythymidinyl, thymidinyl, anhydrothymidinyl, cholesteryl, N6-benzoyl-5'-O-(4,4'-dimethoxytrityl)-2'-deoxyadenosinyl]. The activation of the amino group was performed with trimethylchlorosilane (TMCS).

First Resolution of a Free Fluorophosphine Chiral at Phosphorus. Resolution and Reactions of Free and Coordinated (+/-)-Fluorophenylisopropylphosphine

The trivalent fluorophosphine (+/-)-PFPh(i-Pr), (+/-)-1, has been prepared by halogen exchange of the corresponding chlorophosphine with sodium fluoride in hot sulfolane. The neat fluorophosphine rapidly decomposes by equilibrium redox disproportionation into PF(3)Ph(i-Pr) and (R,R)/(R,S)-Ph(i-Pr)PPPh(i-Pr), but in benzene, (+/-)-1 has considerable thermodynamic stability. The resolution of (+/-)-1 was achieved by a fractional crystallization of the diastereomers (R,R(P))- and (R,S(P))-chloro[1-[1-(dimethylamino)ethyl]-2-naphthalenyl-C,N](fluorophenylisopropylphosphine)palladium(II), (R,R(P))- and (R,S(P))-5, whereby the less soluble (R,R(P)) diastereomer selectively crystallized in 64% yield in a typical second-order asymmetric transformation. Optically pure (S)-(-)-1, -210 (c 0.59, C(6)H(6)), was liberated from (R,R(P))-5 with (R,S)-1,2-phenylenebis(methylphenylphosphine). The optically active phosphine in benzene racemizes over 6 h without significant redox disproportionation. The methoxyphosphine (+/-)-P(OMe)Ph(i-Pr), (+/-)-9, was also resolved by the method of metal complexation. Thus, fractional crystallization of (R,R(P))- and (R,S(P))-chloro[1-[1-(dimethylamino)ethyl]-2-naphthalenyl-C,N](methoxyphenylisopropylphosphine)palladium(II), (R,R(P))- and (R,S(P))-8, followed by liberation of the respective optically active methoxyphosphines from the separated diastereomers with 1,2-bis(diphenylphosphino)ethane, gave (R)-(+)- and (S)-(-)-9 of 92% and 96% ee, respectively. The barrier to unimolecular inversion for (+/-)-9 was determined to be >82.9 +/- 0.5 kJ mol(-)(1) by variable temperature (1)H NMR spectroscopy. The substitution of fluoride in (R,R(P))-5 by methoxide proceeds with predominant inversion of the configuration at phosphorus to give (R,R(P))- and (R,S(P))-8 with (R,S(P))/(R,R(P)) = (1)/(5). The crystal structures of (R,R(P))-5 and (R,R(P))-8 have been determined: (R,R(P))-5 (C(23)H(28)ClFNPPd) crystallizes in the orthorhombic space group P2(1)2(1)2(1) with a = 9.967(2) Å, b = 10.998(4) Å, c = 21.324(3) Å, Z = 4, and R = 0.031; (R,R(P))-8 (C(24)H(31)ClNOPPd) crystallizes in the space group P2(1)2(1)2(1) with a = 10.444(3) Å, b = 12.146(3) Å, c = 19.047(2) Å, Z = 4, and R = 0.026.