Synthetic studies on bafilomycin A1: first formation of the 16-membered macrolide via an intramolecular Stille reaction

The 16-membered macrolide formation of a bafilomycin A₁ synthesis intermediate showed to be very difficult to achieve via an intramolecular Stille reaction. Complex reactions were observed, depending on the nature of the palladium source, ligand, solvent and reaction conditions. Unexpected reactions of the 2-furyl group transfer of trifurylphosphine were observed on the vinylic iodide and (or) the vinylstannane. Best conditions were found with Pd₂(dba)₃/AsPh₃/i-Pr₂NEt in DMF, at 40 °C, to afford the desired macrocycle in 28% yield (33% corrected), the structure of which was definitely confirmed by chemical filiation.     

Towards the synthesis of perfluoroalkylated derivatives of Xantphos

An analogue of Xantphos incorporating four perfluoroalkyl groups has been prepared and successfully used as a ligand in the rhodium-catalysed hydroformylation of 1-octene in toluene. A number of perfluoroalkylated xanthene backbones have also been synthesised, but their conversion into preferentially perfluorocarbon solvent soluble Xantphos-type ligands, suitable for catalysis in fluorocarbon solvents, has not been successful.     

A novel heterobidentate chiral phosphine and its coordination chemistry in transition metal clusters

The optically active ligand R,R-PHAZAN (1,3-bis[(1R)-1-Phenylethyl]-2-(2-thienyl)-1,3,2-diazaphospholane) has been prepared and the products resulting from the reactions with Rh₆(CO)₁₅NCMe, H₃RhOs₃(CO)₁₂, and H₄Ru₄(CO)₁₂ have been investigated by X-ray crystallography and a variety of multinuclear NMR methods. X-ray studies show that PHAZAN can behave as a bidentate ligand in Rh₆(CO)₁₄(μ₂,κ²-R,R-PHAZAN) (with coordination through P and S) or a monodentate ligand (through P coordination) in H₄Ru₄(CO)₁₁(κ¹-R,R-PHAZAN) and NMR studies show that these structures are retained in solution. In Rh₆(CO)₁₄(μ₂,κ²-R,R-PHAZAN), edge-bridging coordination of PHAZAN results in the formation of an additional two novel chiral centres and these are observed in solution. Reaction of PHAZAN with H₃RhOs₃(CO)₁₂ results in cleavage of the thienyl group and formation of the phosphido cluster, H₂RhOs₃(CO)₁₁(μ₂-PNN), (PNN = 1,3-bis-(1-phenylethyl)-[1,3,2]diazaphospholidine-2-yl). A variety of NMR measurements show that the hydride site-occupancies in the solid state are retained in solution and there is evidence for interaction of an ortho-phenyl hydrogen and a hydride through “dihydrogen” bonding.     

Phosphine-catalyzed formal vinylogous aldol reaction of γ-methyl allenoates with aldehydes: easy access to 1,3-dioxanes and dienols

A phosphine-catalyzed formal vinylogous aldol reaction of γ-methyl allenoates with aldehydes is herein reported, in which the γ-methyl group is directly involved in the carbon–carbon bond formation. Under the catalysis of triarylphosphine (20 mol %) and in the presence of a protic additive, γ-methyl allenoates and aldehydes chemo- and stereoselectively produce functionalized 1,3-dioxanes or dienols in modest to good yields. These chemical transformations provide easy excess to oxy-functionalized enoates and dienoates under very mild conditions.     

Fluorinated Heterobutadienes/Trimethylphosphine: A Reactivity Study

The reactions of fluorinated heterobutadienes F 2 C=X--C(R)=Y (X = N, CH; Y = O, N-Mes; R = Ph, t-Bu), A-D , with the PMe 3 were studied. In any case, a different reaction pathway was observed, depending on the specific nature of A-D . These reactions lead to some novel organophosphorus species, including P-ylides and u 5 -azaphosphinines. u 5 -phospholenes, as observed with phosphites, for example, were not observed, but with phosphinidine (P--Ph), the heterobutadienes B and C form u 3 -oxazaphospholenes. Therein the complex (Me 3 P) 3 Ni[cyclo-P(Ph)OC(Ph)NC(CF 3 ) 2 ] was obtained and structurally characterized.     

Chiral Steroidal Phosphines: Synthesis and Platinum Complexes

Summary.  The synthesis of novel 3- and 17-diphenylphosphino-androstane derivatives via homogeneous catalytic P-C coupling is described. The products were characterized by ¹H and ³¹P NMR measurements. According to the NMR investigation of the PtCl₂P₂-type complexes, the steroidal phosphines are trans-coordinated with respect to the Pt-centre exclusively. Received June 14, 2000. Accepted (revised) July 24, 2000     

An efficient and inexpensive scavenger resin for Grubbs’ catalyst

Addition of the inexpensive polymer-bound chelate phosphine 2 to ring-closing metathesis reaction mixtures effectively removes coloured impurities and delivers ruthenium-free (>95%) reaction products.     

Mechanistic investigations of the phosphine-mediated nitrone deoxygenation reaction and its application in cyclic imine synthesis

Carbohydrate-derived cyclic nitrones were deoxygenated to form the corresponding imines using tributylphosphine. Experimental and theoretical investigations by the way of MP2 calculations suggest a revision of the mechanism initially proposed by Kurtzweil and Beak for the triarylphosphine-mediated deoxygenation of nitrones.     

Mononuclear ruthenium complexes containing two different phosphines in trans position: II. Catalytic hydrogenation of CC and CO bonds

Bis(acetate) ruthenium(II) complexes of the general formula Ru(CO)₂(OAc)₂(PⁿBu₃)[P(p-XC₆H₄)₃] (OAc = acetate, X = CH₃O, CH₃, H, F or Cl), containing different phosphine ligands trans to PⁿBu₃, have been employed as catalyst precursors for the hydrogenation of 1-hexene, acetophenone, 2-butanone and benzylideneacetone. For comparative purposes, analogous reactions have been performed using the homodiphosphine precursors Ru(CO)₂(OAc)₂(PⁿBu₃)₂ and Ru(CO)₂(OAc)₂(PPh₃)₂. The catalytic activity of the heterodiphosphine complexes depends on the basicity of the triarylphosphine trans to PⁿBu₃ as this factor controls, inter alia, the rate of formation of hydride(acetate), Ru(CO)₂(H)(OAc)(PⁿBu₃)[P(p-XC₆H₄)₃], or dihydride, Ru(CO)₂(H)₂(PⁿBu₃)[(p-XC₆H₄)₃], complexes, by hydrogenation of the bis(OAc) precursors. The catalytic hydrogenation of the CC double bond is best accomplished by homodiphosphine dihydride catalysts, while heterodiphosphine monohydrides are more efficient catalysts than the homo- and heterodiphosphine dihydrides for the reduction of the keto CO bond.     

Synthesis and Characterization of Mixed-Substituent P- n -Propyl-N-trimethylsilylphosphoranimines

One approach to the synthesis of polyphosphazenes is the condensation polymerization of phosphoranimines. In this work, several novel P-n-propyl-N-trimethylsilylphosphoranimines have been synthesized and characterized. Modifications to the literature synthetic routes were required to obtain the precursor phosphines. The N-trimethylsilylphosphoranimines were obtained though oxidation of the phosphine with bromine and then subsequent nucleophilic displacement using lithium phenoxide. These phosphoranimines were stable for long periods of time under dry inert conditions. NMR analyses revealed complex splitting patterns beyond typical coupling due to the stereocenter at phosphorus. We report several approaches to the n-propyl containing phosphines and phosphoranimines.