Phosphine stereoselective synthesis

Trisubstituted alkenes.9 A stereoselective synthesis of trisubstituted alkenes uses (E)-alkenyl sulfoxides (1)>U as the starting material. These are reduced to the corresponding sulfides (2)," which undergo coupling with Grignard reagents in the presence of complexes of nickel chloride and phosphines as catalyst.12 The products (3) are obtained in steroisomeric purity of > 99%. 

Asymmetric intramolecular Wittig reaction. Trost and Curran2 have examined eight readily available optically active phosphines in a stereoselective synthesis of the ilikctone (2), a useful intermediate to several natural products. Of these, CAMP is dearly the most efficient phosphine for this purpose (equation I). 

S. G. Pyne, Addition of Metalated Allylic Phosphine Oxides, Phosphonates, Sulfones, Sulfoxides and Sulfoximines to a,/3-Unsaturated Carbonyl Compounds , in Stereoselective Synthesis (Houben-Weyl) 4th ed. 1996, (G. Helmchen, R. W. Hoffmann, J. Mulzer, E. Schaumann, Eds.), 1996, Vol. E21 (Workbench Edition), 4, 2068-2086, Georg Thieme Verlag, Stuttgart. 

Evaluation of an Organocyanoborane as Chiral Auxiliary in the Stereoselective Synthesis of Phosphines... 

A simple and efficient stereoselective synthesis of aziridine-2-phosphonate 781 and phosphine oxide 782 was achieved by diastereoselective addition of Grignard reagents to 277-azirine phosphonate 779 and phosphine oxide 780. Addition of benzenethiol and heterocyclic amines proceeded in an analogous manner to yield functionalized aziridines 783 and 784 (Scheme 188). 

Cross-coupling reactions between 1-alkynyl halides and 1-alkenylboranes, which are readily available via hydroboration of alkynes, can also be catalyzed by Pd-phosphine complexes. Stereoselective synthesis of conjugated ( )-enynes 143 was achieved by the coupling of the alkynyl bromide with an alkenylborane [Eq. (48)] [69]. 

Full details have now appeared of the stereoselective synthesis of 1,5,9-triphosphacyclododecane systems by oxidative liberation from molybdenum and chromium complexes of the macrocycle, obtained by coordination-template controlled reactionsMolybdenum complexes have also been used in the coordination-template dependent synthesis of the macrocyclic P,S system 151. A non-template synthesis of the 14-membered P2S2 macrocycle, 152, isolated in two isomeric forms, has been described. Halogenation of the cyclometallated phosphine 153 leads to a rearrangement, with the formation of the di-phosphinobiphenyl system 154, from which the free diphosphine can be liberated... 

Huang, X., Zhang, G., and Lu, X., A convenient stereoselective synthesis of L3-dienylphosphonates and l-en-2-ynylphosphonates and their phosphine oxide analogs. Synthesis. 769. 1995. 

Etemad-Moghadam, G., and Seyden-Penne, J., Stereoselective synthesis of or Z a-methyl a,P-ethylenic esters from phosphonates or phosphine oxides by the Wrttig-Homer reaction. Tetrahedron, 40, 5153, 1984. 

A series of Af-(alk-l-enyl) nucleobase compounds has been prepared by Wittig-Horner reaction of phosphine oxides (165)-(167) or the Horner-Wadswor-th-Emmons reaction of the analogous phosphonates (168) and (169). Hor-ner-Wittig reactions have been utilised for the stereoselective synthesis of single... 

Preparation of Phosphines by Addition of P-H to Unsaturated Compounds. -This route has not received much attention over the past year. A stereoselective synthesis of tris(Z-styryl)phosphine is offered by the addition of phosphine to phenylacetylene in a superbasic system (HMPA-H20-K0H)." In a similar vein, the reaction of phosphine with styrene and a-methylstyrene in a superbasic medium (DMSO-KOH) provides a route to the primary phosphines, (2-phenylethyl)phosphine and (2-methyl-2-phenylethyl)phosphine, respectively. 7 Transition metal phosphine complexes have been shown to catalyse the a-hydroxylation, P-cyanoethylation, and P-alkoxycarbonylethylation of phosphine. 71 Addition of primary phosphines to acrylic esters has been used for the synthesis of the phosphines (80).7 A similar addition of diphenylphosphine to acrylic esters and amides has given a series of hydrophilic phosphines (81). 72 The bis(phosphorinanyl)ethane (82) is formed in the photochemical addition of l,2-bis(phosphino)ethane to 1,4-pentadiene. ... 

A totally stereoselective synthesis of an optically pure carbacycline analog utilized the cycloaddition of the D-(+)-ribonolactone-derived substrate shown in Eq. (54). Initial attempts to achieve cyclization on an analogous substrate with a five-membered ring lactone in place of the seven-membered ring ketal failed, presumably due to the strain that would accompany generation of a trans ring fusion [122]. A number of reactions benefit from the addition of a phosphine oxide. Unfortunately, the effectiveness of this additive is neither general nor predictable, nor is its specific mode of action understood [99],... 

Terpenes.- The first total synthesis of the biologically active marine natural product metachromin A (241) has been achieved using an ( )-stereoselective olefination with the phosphonate (240) as the key step. The olefination reaction of the a-cyanophosphonate (242) with ( , )-farnesal (243) has been studied under a wide variety of conditions with a view to optimising (Z)-stereoselectivity.Excellent (Z)-stereoselectivity was achieved and the resulting procedure applied to a stereoselective synthesis of plaunotol (244). Epimerisation and P-elimination of base-sensitive substrates can cause problems in phosphonate- and phosphine oxide-based olefinations. Such reactions have been excluded in a recent report of enantiospecific syntheses of iridoid monoterpene lactones by intramolecular phosphonate-olefination through the use of mild bases such as DBU and di(wopropyl)ethyl amine/lithium chloride. 

Palladium-complex-promoted asymmetric Diels-Alder reaction stereoselective synthesis of a new sulfinyl-substituted phosphine ligand containing three carbon, one phosphorus and one sulfur stereogenic centres <95CC1747>. 

The first highly stereoselective synthesis of jS-aminophosphinates (613) has been reported by nucleophilic attack of ethyl (1,1-diethoxy-ethyl)methylphosphinate (611) on (iS)-A -(t-butanesulfinyl)imines (610). The reaction product (612) could be subsequently converted into optically pure ethyl jS-amino-TZ-phosphinates (613) (Scheme 153). ° ... 

Yamagishi et al. recently presented a novel method for the stereoselective synthesis of phosphinic pseudopeptide isosteres starting from an enantiopure a-aminoalkyl-//-phosphinate on both a-carbon and phosphorus atoms (36, Scheme 18) [99]. In particular, substrates 37 derived from a stereoretentive Michael addition of aminophosphinates 36 to tert-butyl acrylate, were diastereoselectively alkylated in the Pi position with diastereoisomeric ratios (dr) ranging from 14 1 to 29 1. The stereochemical outcome of this process is highly controlled by the chirahty at the phosphorus atom and the nature of the amino protecting group. 

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