Addition of Secondary Phosphines

Fundamentally, new methods for the synthesis of phosphorus-containing pyrroles from easily available N-vinylpyrroles are developed. Among than is hydrophosphorylation of the vinyl group with secondary phosphines [674], which are now obtained in a one-stage manner from elemental phosphorus and electrophiles in the superbase systems [675,676]. 

SCHEME 2.205 Free-radical addition of secondary phosphines to N-vinylpyrroles. 

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Similar to the addition of secondary phosphine-borane complexes to alkynes described in Scheme 6.137, the same hydrophosphination agents can also be added to alkenes under broadly similar reaction conditions, leading to alkylarylphosphines (Scheme 6.138) [274], Again, the expected anti-Markovnikov addition products were obtained exclusively. In some cases, the additions also proceeded at room temperature, but required much longer reaction times (2 days). Treatment of the phosphine-borane complexes with a chiral alkene such as (-)-/ -pinene led to chiral cyclohexene derivatives through a radical-initiated ring-opening mechanism. In related work, Ackerman and coworkers described microwave-assisted Lewis acid-mediated inter-molecular hydroamination reactions of norbornene [275]. 

Michael addition of secondary phosphines on conjugated olefins is a well known reaction in organic synthesis. Accordingly, addition of diphenylphosphine on hydrophilic activated alkenes in CH3CN or in... 

Transition Metal-Catalyzed Addition of Secondary Phosphine Oxides... 

The addition of secondary phosphines H PR2 to prop-2-ynols in the presence of RuCl (C5Me5)(cod) or RuCl(C5Me5)(PPh3)2 provides the first regio- and stereo-selective direct hydrophosphination of propargylic alcohols and leads to bifunctional... 

The hydrophosphonylation (addition of dialkyl phosphonates), hydrophos-phinylation (addition of alkyl alkylphosphinates or alkyl phosphinates) and addition of secondary phosphine oxides to unfunctionalized alkenes and alkynes occur under free radical conditions or with transition metal catalysis.10,39 63 90... 

The Michael addition of secondary phosphine oxides to o ,/ -unsaturated esters proceeds with very high stereoselectivity. Thus, in the reaction of benzylphenylphosphine oxide with methyl ( )-2-methyl-2-butenoate, only two of the four possible diastereomers (PR)-7 and (P51)- are formed and in a 1 1 ratio they have the same relative configuration at the 1- and /1-carbon atoms, but differ in the configuration at phosphorus10. 

Michael addition of secondary phosphine oxides to cyclohexene-1-carboxylates (both flexible and biased) gives exclusively the axially substituted products 810. 

Free radical-induced additions have been used in the synthesis of a range of phosphines bearing other nucleophilic groups, e.g., (41), useful for specific peptide bond cleavage of proteins.A further example of the formation of the phosphorinanone system by addition of phenylphosphine to a divinyl ketone derivative has been described.Two reports have appeared of the addition of secondary phosphines to maleic anhydride and related activated olefins, to give functionalised tertiary phosphines, e.g., (42). A route to allylphosphines is provided by base-... 

The hydroquinine thiourea catalyst 81a was also identified by Melchiorre and coworkers as a promising catalyst for the asymmetric addition of secondary phosphines 1SS to aromatic nitroalkenes 130 furnishing 156 (obtained after protection with in situ formed borane) [46]. However, the obtained ee values were only moderate (up to 66% ee) (Scheme 9.53). 

The addition of secondary phosphines to vinylaminophosphines, e.g. (23), occurs under both free-radicaP and base-catalysed conditions to form, e.g., (24) or (25). Similar addition of primary phosphines to (23) occurs to form either polymers, e.g. (26), or diphosphacyclohexanes, e.g. (27), depending on the mode of initiation. 

Michael addition of secondary phosphines on conjugated olefins is a well known reaction in organic synthesis. Accordingly, addition of diphenylphosphine on hydrophilic activated alkenes in CH3CN or in CH3CN/H20 solution leads to various tertiary phosphines [33] examples include 1, 25, 27. In order to avoid the formation of phosphine oxides and/or the hydrolysis of some alkene derivatives (e.g. acryl esters) a small amount of Et N+OH" was used as base, and a small quantity ofditertbutylphenol was... 

Addition of secondary phosphine oxides, which are structurally analogous to dialkyl phosphites, to aldehydes and ketones was mentioned in the preceding Section.cf 101 Secondary phosphine oxides are, however, not always easy to prepare and can be replaced by their salts which are prepared from the phos-phinic chlorides and sodium or Grignard solutions.102 The same salts are obtained from dialkyl phosphites (cf. page 746). 

Cyanoethylphosphine oxides (13a) and sulphides (13b) are produced by the base-catalysed addition of secondary phosphine oxides or sulphides... 

U.v.-induced addition of secondary phosphines to chlorovinylsilanes and allyl(chloro)silanes leads to the silylphosphines (36). A similar addition to vinyl-substituted heterocyclic silanes has given compounds such as (37). ... 

The addition of secondary phosphines to acrylic acid systems in the presence of acid, followed by treatment with alkali, leads to the phosphinocarboxylates (41). Addition of P-H to carbonyl groups has been employed in the synthesis of the heterocyclic system (42), and to C=N units in the synthesis of the form-amidinophosphines (43). The reaction of phenyl(trimethylsilyl)phosphine to... 

A new synthesis of vinylphosphine oxides is available from the addition of secondary phosphine oxides to enol acetates to give (43), followed by thermolytic... 

Reactions of fluoroalkylketenimines which have been reported following these newly available synthetic approaches include hydrolysis and related additions of amines and alcohols, all of which occur at the olefinic bond. In contrast, the apparently similar addition of secondary phosphines occurs at the carbon-nitrogen double bond. These ketenimines appear to enter into cycloaddition reactions very readily with acetylenes they give quinolines, with nitrones they give oxindoles or oxadiazolidines (see p. 107), i > i and with isocyanides they yield iminoindolenines. These reactions are summarized in Scheme 54. 

The radical addition of secondary phosphine ehalcogenides was also extended to a tetravinyl ether to furnish hyper-branched dendrimer-like tetraphosphine chalcogenides (Scheme 24). A part of the products was also prepared by the addition of secondary phosphines followed by reaction with O, Sg or Se. 

The similar reaction of diarylphosphine oxides with aryl halides and triflates has been used more recently to prepare a variety of ligands for asymmetric catalysis. Many of these reactions involve additions of secondary phosphine oxides to di- or monotriflates derived from binaphthol because the triflates are more accessible than 2,2 -l,l -dibro-mobinaphthol. Workers at Syntex described a procedure to use the ditriflate of binaphthol to prepare mixed phosphine oxide, hydroxo ligands, and the monophosphine oxide, bi-naphthyldiphenylphosphine oxide. Hayashi then developed a route to a number of chiral monodentate phosphine ligands with a 2-(diphenylphosphino)-2 -alkoxy-l,l -binaphthyl structure (Eq. Reaction of the ditriflate with diphenylphosphine oxide in the... 

Examples of electrophilic addition of secondary phosphines to alkenes or alkynes were described. [114, 124, 125, 135]. Glueck [124-126] reported enantioselective tandem reaction of alkylated/arylation of primary phosphines catalyzed by platinum complex, proceeding with formation of chiral phosphaace-naphthenes. Palladium-catalyzed hydrophosphination of alkynes 219 tmder kinetic resolution conditions gave access to 1,1-disubstituted vinylphosphine boranes 220. However, despite screening several chiral ligands, temperatures, and solvents, the... 

Cole-Hamilton and coworkers [132] anchored trialkylphosphines on polyhedral oligomeric silsesquioxanes (POSS) (Scheme 2.37). The dendrimer-bound phosphines were placed on the periphery of the dendrimer either by radical addition of secondary phosphines to vinyl groups or by reaction of Si-Cl bonds... 

Before starting a synthesis, the chemistry should be evaluated to determine whether or not a solvent is actually needed. In many cases, reactions are faster, cleaner, and more efficient in the absence of a solvent. In the extreme case, the desired reaction will only occur in the absence of a solvent. The iron-catalyzed addition of secondary phosphines to alkynes is an example of such a reaction (Scheme 1.4) [9]. In the absence of solvent, this double addition reaction cleanly affords the 1,2-bisphosphine in excellent yield. When solvents were added to the reaction, the addition reaction was completely suppressed. 

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