Arnaud Voituriez

2-Phospha[3]ferrocenophanes with Planar Chirality : Synthesis and Use in Enantioselective Organocatalytic [3 + 2] Cyclizations

Planar chiral phosphines displaying a new ferrocenophane scaffold have been prepared via a stereoselective approach. The P-cyclohexyl substituted phosphine affords high levels of asymmetric induction in the organocatalytic [3 + 2] annulation reaction between allenes and electron-poor olefins.

An Organocatalytic [3+2] Cyclisation Strategy for the Highly Enantioselective Synthesis of Spirooxindoles

Spirooxindole cores are featured in a number of natural and unnatural biologically active compounds, as well as in drug candidates. Among them, pyrrolidin-3,3’-oxindole units are the most widespread, however, spirocyclic oxindoles with carbocyclic fiveor six-membered rings are not uncommon either. Specifically, 3-spirocyclopentane-2-oxindole scaffolds are embodied in natural alkaloid derivatives such as marcfortines, citrinadins cyclopiamines, notoamides and versicolamides. They also find applications in the area of medicinal chemistry.

Helicenes with Embedded Phosphole Units in Enantioselective Gold Catalysis

This paper discloses the first uses of phosphahelicenes as chiral ligands in transition-metal catalysis. Unlike all known helical phosphines used so far in catalysis, the phosphorus function of phosphahelicenes is embedded in the helical structure itself. This crucial structural feature originates unprecedented catalytic behaviors and efficiency. An appropriate design and fine tuning allowed both high catalytic activity and good enantiomeric excesses to be attained in the gold promoted cycloisomerizations of N-tethered 1,6-enynes and dien-ynes.

Expanding the Scope of Enantioselective FerroPHANE‐Promoted [3+2] Annulations with α,β‐Unsaturated Ketones

The planar chiral 2-phospha[3]ferrocenophane I has been shown to be the first efficient nucleophilic organocatalyst for the enantioselective synthesis of cyclopentenylphosphonates, through [3+2] cyclizations between diethyl allenylphosphonate and alpha,beta-unsaturated ketones. The same catalyst has also been applied to the highly enantioselective [3+2] cyclizations of allenic esters with dibenzylideneacetone and analogous bis-enones, leading to functionalised cyclopentenes with either monocyclic or spirocyclic structures (ee 84-95 %). It has been shown that the residual enone functions in the resulting cyclopentenes can be involved in subsequent cyclization steps to afford unprecedented C(2)-symmetric bis-cyclopentenylketones. In order to provide insight into the behaviour of FerroPHANE I as a chiral catalyst in [3+2] cyclisations, the energetically most favoured isomers of the key phosphine-allene adduct have been calculated by DFT methods. Factors likely to control the chiral induction process are highlighted.

Synthesis of 3,3′-Spirocyclic Oxindoles via Phosphine Catalyzed [4 + 2] Cyclizations

Triphenylphosphine promoted reactions between 3-arylideneoxindoles and δ-aryl-substituted penta-2,3-dienoates afford an unprecedented access to spirocyclic oxindoles with functionalized six-membered rings. In these new [4 + 2] cyclization processes, the allenoates operate as the four-carbon synthons, thanks to the involvement of the substituted δ-carbons. These reactions give excellent control of the relative stereochemistry of the three stereogenic centers. The stereochemistry of the final product has been ascertained by X-ray diffraction studies.

Phosphahelicenes in Asymmetric Organocatalysis: [3+2] Cyclizations of γ‐Substituted Allenes and Electron‐Poor Olefins

The first use of phosphahelicene in enantioselective organocatalysis is reported. New chiral phosphahelicenes have been prepared and enable highly enantioselective [3+2] cyclization reactions between arylidene- or alkylidenemalononitriles and γ-substituted allenoates or cyanoallenes. These reactions afford cyclopentene derivatives in both high yields and diastereoselectivities, with enantiomeric excesses of up to 97 %.

Phosphine Organocatalysis in the Synthesis of Natural Products and Bioactive Compounds

During the last few years, synthetic methods based on phosphine organocatalysis have experienced extremely fast developments. This short overview is intended to demonstrate that these methods can afford suitable tools for the constitution of either focused or diversity‐oriented‐synthesis (DOS) inspired libraries of small molecules for biological screening. It also reports selected examples where these organocatalytic methods have been used conveniently as key steps in the formal or total synthesis of complex natural products. Especially, synthetic applications of the inter‐ and intramolecular cyclizations of unsaturated substrates have been considered in this review.

Phosphathiahelicenes: Synthesis and Uses in Enantioselective Gold Catalysis

Enantiomerically pure thiahelicenes displaying a terminal phosphole unit and a stereogenic phosphorus center have been prepared by oxidative photocyclization of a diaryl-olefin precursor. Starting from one of these phosphathiahelicene oxides, the corresponding trivalent phosphine-Au(I) complex is obtained with complete diastereoselectivity. It affords a new, excellent precatalyst for the enantioselective cycloisomerization of N-tethered enynes (up to 96 % ee).

Phosphine-Catalyzed Synthesis of 3,3-Spirocyclopenteneoxindoles from γ-Substituted Allenoates: Systematic Studies and Targeted Applications

The phosphine-promoted [3 + 2] cyclizations between γ-substituted allenoates and arylideneoxindoles have been applied to the stereoselective synthesis of spiro(cyclopentene)oxindoles with trisubstituted cyclopentene units. It has been demonstrated that PPh(3) operates a very efficient control of the relative stereochemistry of the three stereogenic centers of the final spiranic products. Focused experiments have been carried out then so as to access carbocyclic analogues of an important series of anticancer agents inhibiting MDM2-p53 interactions.

Preparation of a Storable Zinc Carbenoid Species and Its Application in Cyclopropanation, Chain Extension, and [2,3]-Sigmatropic Rearrangement Reactions

The formation of a new phosphate carbenoid (n-BuO)(2)P(O)OZnCH(2)I and its application in organozinc-mediated reactions is described. This carbenoid undergoes very slow degradation in solution and can be stored for several weeks at -20 degrees C. Its reactivity was tested with many representative alkenes and was determined to be a powerful cyclopropanating reagent, giving the corresponding cyclopropanes in 72-99% yield. The use of this carbenoid in the chain extension of 1,3-diketones and [2,3]-sigmatropic rearrangement reactions is also described.