Stereoselective synthesis of P-chirogenic dibenzophosphole-boranes via aryne intermediates

A new aryne-mediated tandem cross-coupling/P-cyclization sequence starting from tertiary phosphine-boranes and 1,2-dibromobenzenes is reported. P-chirogenic dibenzophospholes become accessible in a regio-, chemo-, and diastereoselective way.     

Enantiodivergent synthesis of P-chirogenic phosphines

Several approaches for the enantiodivergent synthesis of P-chirogenic mono- and diphosphines are described, using ephedrine methodology and phosphine borane chemistry. Firstly, both enantiomers of a tertiary phosphine can be obtained starting from the same oxazaphospholidine borane complex, prepared from (+)-ephedrine, when changing the order of addition of the organolithium reagents during the synthetic pathway. The second approach is based on the chlorophosphine boranes, which react with an organolithium reagent, to afford the corresponding phosphines with inversion of configuration. In the case where the chlorophosphine borane reacts with the t-butyl lithium reagent, a metal-halogen exchange occurs to afford the corresponding phosphide borane with retention of the configuration. The reaction of the phosphide borane with an alkyl halide leads to the same phosphine, but with the opposite configuration. Another approach depends on the diastereoselective preparation of the starting oxazaphospholidine borane complex from (?)-ephedrine, which leads according the case, to either one or the other enantiomer of a phosphine. Finally, the synthesis of (R,R)- and (S,S)-1,2-bis(methylphenylphosphino)ethane is also demonstrated using both enantiomers of the P-chirogenic diphosphinite diborane, which simultaneously allows the introduction of alkyl- or aryl substituents on the phosphorus atoms. In summary, these approaches show the great efficiency of the “ephedrine methodology” for the enantiodivergent synthesis of P-chirogenic mono- and diphosphines, and bearing alkyl or aryl substituents.     

Modular synthesis of ChiraClick ligands: a library of P-chirogenic phosphines

A library of novel and diverse P-chirogenic phosphine ligands containing a triazole moiety (ChiraClick ligands) were prepared in high yield in a modular fashion that allows for variation of both the phosphine and the triazole structure, as well as giving access to the two enantiomers of the ligand.     

Stereoselective synthesis of phosphinite complexes new route to chiral phosphines

Consecutive substitutions of chlorine in dichlorophenylphosphine by lithium cinchoninate and arylcyanocuprates lead stereoselectively to the corresponding $\text{R}$ P^III esters ; the latter are converted, by methyllithium, into chiral phosphines.     

Synthesis of diphenyl[alkyl(aryl)trimethylsiioxymethyl]phosphines

A series of previously unknown diphenyl[alkyl(aryl)trimethylsiloxymethyl]phosphines was prepared by the reaction of diphenyl(trimethylsilyl)phosphine with carbonyl compounds. The first complexes of these ligands with palladium chloride were prepared.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 754–756, April, 1994.     

Thermal chemistry of poly(aryl ether phthalazine)s and the synthesis of poly(aryl ether quinazoline)s

Poly(aryl ether phthalazine)s were found to undergo an exothermic reaction at a temperature range of 360–440°C. We elucidated the origin of the exothermic reaction and the physiochemical phenomena associated with it, based on thermal analyses, model compound studies, and ¹³C solid-state NMR studies. At elevated temperatures, polymers containing a diphenylphthalazine moiety 4 underwent extensive thermal crosslinking reactions as a result of a nitrogen elimination reaction of the phthalazine moiety. However, polymers containing the tetraphenyl or hexaphenyl phthalazine moiety 5 and 6 were found to undergo principally a backbone rearrangement reaction, in which the phthalazine moiety rearranged to a quinazoline. Utilizing this efficient thermal rearrangement of polyphenylated phthalazines, we have prepared a novel activated difluoride, 2,4-bis(4-fluorophenyl)-,5,6,7,8-tetraphenylquinazoline 9d, which underwent high-temperature solution polycondensation with BPA to give the quinazoline containing poly(aryl ether) 14. Polymer 14 is amorphous, has a glass transition temperature of 264°C, and has high thermooxidative stability with 5% weight loss being recorded at 514°C in nitrogen. © 1996 John Wiley & Sons, Inc.     

The synthesis of tris(perfluoroalkyl)phosphines

Tris(perfluoroalkyl)phosphines, of interest as tunable alternatives to the carbon monoxide ligand, can be synthesised by the nucleophile mediated reaction of perfluoroalkyltrimethylsilanes with triphenylphosphite; the method can be extended to diphosphines.     

The synthesis of perfluoro(alkyletherphenyl) phosphines

The first perfluorophenyl substituted phosphine, C₆F₅)₃P was prepared by Wall et al. [1]. Since then numerous pentafluorophenylphosphorous compounds [2] have been prepared and their properties studied. Substituted perfluorophenylphosphines (R_fC₆F₄)₃P however not been extensively studied. Those that have been reported are all solids: (C₆F₅)₃P, m.p. 116° [1]; (p-CF₃C₆F₄)₃P, m.p. 103-105° [3]; (p-C₈F₁₇C₆F₄)₃P m.p. 117° [3]; and (p-C₆F₅OC₆F₄)₃P, m.p. 135-137° [4].     

Design and synthesis of tris[bis(benzylammonium)aryl]phosphines with bulky meta-substituents

A novel 3,5,3′,5′,3″,5″-hexakis(dimethylamino)methyl substituted triphenylphosphine analogue has been prepared. The six amine functionalities of the corresponding phosphine oxide and sulfide were alkylated quantitatively with methyl iodide and benzyl bromide, as well as with G1 and G2 Fréchet dendrons to afford the respective hexa-ammonium triarylphosphine oxides and sulfides. The phosphine sulfide derivatives were deprotected with P(n-Bu)₃ to afford a series of hexa-ammonium triarylphosphines that range from small molecules to first and second generation dendrimers (MW up to 5451.44). Upon formation of the hexa-ammonium salt a clear shift in ³¹P NMR is observed, indicative for opening of the C-P-C angle of the triaryl phosphine. Calculations on the hexacationic phosphines show an increased barrier of rotation around the P-C(aryl) bond with increasing size of the N-substituents. The calculated structure of the G2-dendron alkylated hexa-ammonium triarylphosphine shows that this dendritic phosphine has a disc-like rather than a cone-like structure, with an estimated cone angle of approximately 180°     

Stereoselective synthesis of tetrasubstituted (Z)-alkenes from aryl alkyl ketones utilizing the Horner-Wadsworth-Emmons reaction

Tetrasubstituted (Z)-alkenes were readily prepared through the Horner-Wadsworth-Emmons reactions of methyl 2-[bis(2,2,2-trifluoroethyl)phosphono]propionate with aryl alkyl ketones by employing Sn(OSO(2)CF(3))(2) and N-ethylpiperidine.     

P-Modular bis(phosphines) based on the 1,2-trans-disubstituted cyclopentane framework in synthesis, coordination chemistry, and catalysis

The review describes a class of versatile bidentate phosphines having a homochiral 1,2-disubstituted cyclopentane backbone, the use of such ligands in coordination chemistry, and their application in transition metal-catalyzed synthesis, including CH activation, CC coupling, CC hydrogenation, and hydroformylation. In particular, the synthetic potential of the multi-purpose PH and PCl reagents (R,R)- and (S,S)-C₅H₈(PX₂)₂ (X = H, Cl) is highlighted, since these open up the possibility to incorporate virtually any other PO-, PN- or PC-bonded residue (“module”) into the homochiral bis(phosphine) framework. The resulting chelate ligands allow access to transition metal catalysts with stereodiscriminating properties determined by parameters such as (i) the presence of P-substituents that are equal or pairwise different in steric demand, (ii) the spatial orientation of such substituents with respect to the coordination plane of the catalyst complex, and (iii) the combination of C- and P-chirogenic stereoelements in matched (or mismatched) fashion. A comparative discussion of the crystal structures that are currently available for the free ligands and their transition metal complexes is also presented.     

Stereoselective synthesis of (±)-palitantin

Stereoselective synthesis of (±)-palitantin has been completed.     

Stereoselective synthesis of (−)-ara-cyclohexenyl-adenine

A stereoselective synthesis leading to (−)-ara-cyclohexenyl-adenine is described. The synthesis starts from methyl-α-d-glucopyranose and involves an isomerization step, selective protection/deprotection chemistry, a Ferrier rearrangement and a Mitsunobu reaction. This is the first total synthesis of an enantiomeric pure ara-type cyclohexenyl nucleoside.     

Stereoselective synthesis of (±) - laurene

Reduction of an unsymmetrically substituted unsaturated aldehyde by way of the corresponding tosylhydrazone is shown to proceed stereoselectively.     

Stereoselective synthesis of (±)-tacamonine

We report a stereocontrolled approach to the pentacyclic indole alkaloid tacamonine by modifying an earlier route using norbornadiene to supply the nontryptamine portion. By maintaining a bridged system the reduction step of the Bischler-Napieralski reaction proceeded to deliver a bridged diol in which three methine hydrogen atoms are in an all-cis configuration. All 19 skeletal carbon atoms are fully incorporated, therefore, the only remaining steps involved cleavage of the vic-diol subunit in the seven-membered ring and further oxidation and reduction of the resulting lactam aldehyde.     

Stereoselective synthesis of (−)-microcarpalide

A stereoselective approach for the synthesis of the bio-active decanolactone (−)-microcarpalide was achieved from chiral pool tartaric acid. The synthesis of pivotal intermediates en route to the decanolactone was achieved from α-benzyloxy aldehydes derived from l- and d-tartaric acid.     

Stereoselective synthesis of (-)-acanthoic acid

[reaction: see text] The first stereoselective synthesis of (-)-acanthoic acid (1) has been designed and accomplished. Our synthetic plan departs from (-) Wieland-Miesher ketone (7) and calls upon a Diels-Alder cycloaddition reaction for the construction of the C ring of 1. The described synthesis confirms the proposed stereochemistry of 1 and represents an efficient entry into an unexplored class of biologically active diterpenes.