Phosphines Asymmetric synthesis

Anderson BJ, Guino-o MA, Glueck DS, Golen JA, DiPasquale AG, Liable-Sands LM, Rheingold AL (2008) Platinum-catalyzed enantioselective tandem alkylation/arylation of primary phosphines. Asymmetric synthesis of P-steieogenic 1-phosphaacenaphthenes. Org Lett 10 4425 28... 

A number of excellent reports which deal with synthesis of optically active phosphine ligands are available to date, and have been referenced in this chapter. Therefore it is not the intention here to overlap with them, but rather to describe recent advances in the field. Thus, this chapter is intended to serve as a review to the preparation of some efficient P-chirogenic compounds which have been developed over the past ten years, by either resolution or asymmetric synthesis. Considerable progress has been made in the preparation and use of P-stereogenic compounds. Use of newer methods is stressed here however an at-... 

Chiral phosphine based transition metal complexes are nsed as a powerful tool for asymmetric synthesis (3). A fundamental mechanistic nnderstanding is required for rhodium and mthenium catalyzed reactions. The starting point of those investigations was the clear and detailed stractnral description of the isolated pre catalyst system. 

A modification of this procedure allowed the isolation of 1,3,2-oxazaphospholidine 52a as a single diastereomer [41] and its application to asymmetric synthesis of enantiomerically and diastereomerically pure phosphinic acid derivatives 53 and 54 and tertiary phosphine oxides 55 (Scheme 20) [45], A few years later, a similar approach for the synthesis of enantiomerically pure tertiary phosphine oxides 55... 

The asymmetric hydrosilylation that has been most extensively studied so far is the palladium-catalyzed hydrosilylation of styrene derivatives with trichlorosilane. This is mainly due to the easy manipulation of this reaction, which usually proceeds with perfect regioselectivity in giving benzylic silanes, 1-aryl-1-silylethanes. This regioselectivity is ascribed to the formation of stable 7t-benzylpalladium intermediates (Scheme 3).1,S Sa It is known that bisphosphine-palladium complexes are catalytically much less active than monophosphine-palladium complexes, and, hence, asymmetric synthesis has been attempted by use of chiral monodentate phosphine ligands. In the first report published in 1972, menthyldiphenylphosphine 4a and neomenthyldiphenylphosphine 4b have been used for the palladium-catalyzed reaction of styrene 1 with trichlorosilane. The reactions gave l-(trichlorosilyl)-l-phenylethane 2 with 34% and 22% ee, respectively (entries 1 and 2 in Table l).22 23... 

For general application of these chiral ligands, see (a) Kagan, H. B. Chiral Ligands for Asymmetric Catalysis in Morrison, J. D. ed. Asymmetric Synthesis, vol. 5, Chap. 1, Academic Press, New York, 1985. (b) Kagan, H. B., Sasaki, M. Optically Active Phosphines Preparation, Uses and Chiroptical Properties in Hartley, F. R. ed. The Chemistry of Organo Phosphorous Compounds, John Wiley Sons, New York, 1990, vol. 1, Chap. 3. 

A synthesis of novel chiral phosphine oxide aminal 113 has been developed by reacting phosphine oxide aldehyde 111 with diamine 112. The condensation gave a single diastereomer of the phosphine oxide aminal in 65% yield. This compound can be used as chiral auxiliary in asymmetric synthesis (Equation 15) <1996TA3431, 1996TL3051, 1996TL7465>. 

In 2001, a palladium-catalyzed asymmetric hydrosilylation of 4-substituted-but-l-en-3-ynes (146) was reported by Hayashi and co-workers [115]. It was found that a monodentate bulky chiral phosphine, (S)-(R)-bisPPFOMe, was effective for the asymmetric synthesis of the axially chiral allenes 147 and up to 90% ee was achieved (Scheme 3.75). The bulky substituent at the 4-position in 146 is essential for the selective formation of the allene 147 the reaction of nC6H13C=CCH=CH2 gave a complex mixture of hydrosilylation products which consisted of <20% of the allenylsilane. 

The asymmetric synthesis of allenes via enantioselective hydrogenation of ketones with ruthenium(II) catalyst was reported by Malacria and co-workers (Scheme 4.11) [15, 16]. The ketone 46 was hydrogenated in the presence of iPrOH, KOH and 5 mol% of a chiral ruthenium catalyst, prepared from [(p-cymene) RuC12]2 and (S,S)-TsDPEN (2 equiv./Ru), to afford 47 in 75% yield with 95% ee. The alcohol 47 was converted into the corresponding chiral allene 48 (>95% ee) by the reaction of the corresponding mesylate with MeCu(CN)MgBr. A phosphine oxide derivative of the allenediyne 48 was proved to be a substrate for a cobalt-mediated [2 + 2+ 2] cycloaddition. 

In 1993, Hayashi and co-workers reported a catalytic asymmetric synthesis of alle-nylboranes 256 by palladium-catalyzed hydroboration of conjugated enynes 253 (Scheme 4.66) [105]. Reaction of but-l-en-3-ynes 253 with catecholborane 254 in the presence of a catalyst, prepared from Pd2(dba)3 CHC13 (1 mol%) and a chiral mono-dentate phosphine ligand (S)-MeO-MOP 255 (1 mol%), gave an allenylborane 256. The ee of 256 was determined by the reaction with benzaldehyde affording the corresponding optically active homopropargyl alcohols 257 with up to 61% ee (syn anti= 1 1—3 1). 

Such diene complexes can be used to prepare homogeneous hydrogenation catalysts in situ, especially where a variable tertiary phosphine/rhodium ratio is required3 or where an asymmetric tertiary phosphine is employed for asymmetric synthesis.4 The cyclooctadiene complex is also the starting point for the preparation a number of complexes of the type [Rh(l, 5-C8H12)L2]+ (L represents a variety of P— and N— donor ligands) of interest in homogeneous catalysis.s... 

The reduction of double bonds using chiral phosphine ligands as the precursors for the appropriate catalysts is a widely used strategy in the asymmetric synthesis of... 

Use of chiral ligands allows asymmetric synthesis of optically active branched aldehydes. In the early 1970s, two groups independently reported the first examples of asymmetric hydroformylation (109). Optical yields of less than 2 % were obtained by using styrene as substrate and a chiral Schiff base-Co or phosphine-Rh complex as catalyst. 

The biological properties of phosphorus amino acid analogues (and their derivatives) depend upon their stereochemistry. Consequently, numerous methods for obtaining these compounds in stereochemically pure form have been developed. Two excellent review articles summarize the work performed prior to 1993. 3,4 Resolution of racemates continues to be a useful approach for obtaining optically pure aminoalkylphosphonic and -phosphinic acid derivatives (vide infra), but most of the newer literature describes asymmetric syntheses of these compounds.15-17 Two methods for resolution and one for asymmetric synthesis are described (vide infra) they have been selected since they are relatively easy to perform, work with a variety of side chains, can be carried out on a reasonable scale with readily available starting materials, and produce products of high stereopurity. However, just as in traditional amino acid chemistry, each side chain introduces its own complications, and in many cases, especially for more complex analogues, other methods may be preferred. 

Wilkinson s (I) discovery that the soluble rhodium(I) phosphine complex, [Rh(PPh3)3Cl], was capable of homogeneous catalytic hydrogenation of olefins immediately set off efforts at modifying the system for asymmetric synthesis. This was made possible by the parallel development of synthetic methods for obtaining chiral tertiary phosphines by Horner (2) and Mislow (3,4, 5). Almost simultaneously, Knowles (6) and Horner (7) published their results on the reduction of atropic acid (6), itaconic acid (6), a-ethylstyrene (7) and a-methoxystyrene (7). Both used chiral methylphenyl-n-propyl-phosphine coordinated to rhodium(I) as the catalyst. The optical yields were modest, ranging from 3 to 15%. 

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