Nucleophiles phosphorus

Both neutral and anionic phosphorus compounds are good nucleophiles toward alkyl halides. Examples of these reactions were already encountered in Chapter 2 in connection with the preparation of the valuable phosphorane and phosphonate intermediates used for Wittig reactions  

The reaction with phosphite esters is known as the Michaelis-Arbuzov reaction and proceeds through an unstable trialkoxyphosphonium intermediate. The second stage in the reaction is another example of the great tendency of alkoxyphosphonium ions to react with nucleophiles to break the O—C bond, resulting in formation of phosphoryl P=0 bond. 

The reaction with phosphite esters is known as the Michaelis-Arbuzov reaction and proceeds through an unstable trialkoxyphosphonium ion intermediate. The 

The reaction of a-bromoketones with phosphines and phosphites can take a competitive course in which phosphorus attacks at bromine. In protic solvents the enolate intermediate is protonated so that the overall course of the reaction is dehalogenation of the ketone  

SECTION 3.3. NUCLEOPHILIC CLEAVAGE OF CARBON-OXYGEN BONDS IN ETHERS AND ESTERS 

SECTION 3.2. INTRODUCTION OF FUNCTIONAL GROUPS BY NUCLEOPHILIC SUBSTITUTION AT SATURATED CARBON 

When phosphite esters are used as nucleophiles, the stable product is an enol phosphate  

Trialkyl- and triaryl-phosphines react with 1,3-benzodithiolylium ions to give a phosphonium salt which is deprotonated by n-butyllithium to give (282) (76TL3695). 

All varieties of alkynyliodonium salts readily react with triphenylphosphine resulting in the corresponding alkynylphosphonium salts in excellent yields. For cample, reaction of alkynyliodonium triflates with PhjP in cold dichloromethane gives alkynylphosphonium salts, 95, in nearly quantitative yields [75] [Eq. (50)J. 

Likewise, the bis-iodonium diyne triflates 34 and 35 give the bisphosphonium diynes 96 and 97 in high isolated yields [40] [Eqs. (51), (52)]. 

Advantage has been taken of the ready interaction of phosphines with alkynyliodonium salts in the alkynylation of tetra(t-butyl)tetraphosphacubane, 98, to give the phosphacubane salt, 99 [76] [Eq. (53)]. 

Similarly, reaction of t-butylethynyliodonium tosylate with bis(diphenylphosphino)methane, 100, in benzene gives the novel 1 X. ,3X, -diphospholium ion, 101, in 77% yield [77] [Eq. (54)]. 

Trialkyl phosphites undergo reaction with alkynyliodonium tosylates, resulting in dialkyl alkynylphosphonates, 102, via an Arbuzov-type process [78] [Eq. (55)]. 

Hoffman and Rabe have successfully converted the a-methylene-p-acetoxy-alkanoates and 2-bromomethyl-2-alkenoates into (2 )-2-methylalkenoates and 

MBH acetates were found to undergo a nucleophilic substitution reaction when treated with magnesium bromide to produce the corresponding allyl bromide, (Z)-366 and ( )-367, with high stereoselectivity. This reaction 

Ar = Ph, 2-CIPh, 4-CIPh, 4-MePh, 3,4-(OCH20)Ph, 2-MeOPh, 4-MeOPh, 3-BrPh, 2-fuiyl 

Tom and co-workers have elegantly demonstrated the role of intramolecular hydrogen bonding for diastereoselectivity as well as reactivity towards radical addition onto MBH adducts. Thus, the reaction of (25,5s)-a-(1-hydroxyethyl)vinyl sulfoxide 387 with alkyl radical and BusSnH gave the 

A similar photoreaction of the MBH adduct derived from cyclohept-2-enone gives 1,4-diketones 398 and 399 without ring contraction, whereas the MBH adduct obtained from y,y-disubstituted cyclohex-2-enone gives 1,4-diketones 

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Reaction with Phosphorus Nucleophiles. The ethyleneknine ring can be opened using phosphines (91) or alkaU metal phosphides (92) ... 

Kinetic studies have shown that the enolate and phosphorus nucleophiles all react at about the same rate. This suggests that the only step directly involving the nucleophile (step 2 of the propagation sequence) occurs at essentially the diffusion-controlled rate so that there is little selectivity among the individual nucleophiles. The synthetic potential of the reaction lies in the fact that other substituents which activate the halide to substitution are not required in this reaction, in contrast to aromatic nucleophilic substitution which proceeds by an addition-elimination mechanism (see Seetion 10.5). 

Recently developed trifluoromethylatmg agents capable of transferring the trifluoromethyl group as a cation to strongly nucleophilic compounds such as carbanions and sulfur and phosphorus nucleophiles are prepared from o-biphenyl trifluoromethyl sulfoxide [164] and are shown in equation 141... 

Phosphorus nucleophiles have received little attention compared with nitrogen nucleophiles in reactions with fluonnated systems Yields with phosphorus nucleophiles are sometimes low, but interesting materials are obtained [80, 81] (equations 42 and 43). 

Trichloro-s-triazine also reacts readily with carbon or phosphorus nucleophiles. Diethylmalonate anion forms a mono-derivative under mild conditions and the tri-substitution product (327) under vigorous conditions with excess nucleophile. Nucleophilic attack by the 7r-electrons of ketene diethylacetal to give 254 and of dimethylaniline to give 253 has been mentioned earlier. Two... 

The influence of substituents in Ar1 is characterized by negative p values (plot based on ordinary Hammett a constants)208. Reactions involving other types of phosphorus nucleophiles (e.g. PPh2Alk)208 and ArS02 ions as nucleophiles have also been studied209. The work has been extended to the study of a-azidosulfones but the reaction does not turn out to be analogous210. There is base-catalyzed abstraction of hydrogen ion from the a-carbon atom. 

The phosphinic isocyanates (116) and isothiocyanates (117) react with oxygen, nitrogen, and phosphorus nucleophiles by attack at carbon rather than phosphorus. Phenyl phosphonodichloridate has been recommended as a useful reagent for the activation (presumably by mixed anhydride formation) of carboxylic acids for conversion to amides and hydrazides. ... 

Sections I and J of Scheme 3.2 show reactions with sulfur and phosphorus nucleophiles. The reaction in Entry 25 is a useful method for introducing thiol groups. The solid thiourea is a convenient source of sulfur. A thiouronium ion is formed and this avoids competition from formation of a dialkyl sulfide. The intermediate is readily hydrolyzed by base. 

The reactions of white phosphorus with tetraalkylammonium cyanides in the presence of a crown ether in acetonitrile give rise to the dicyanophosphide ion, which is found to react with a variety of anionic phosphorus nucleophiles with displacement of cyanide ion to generate new P-P bonded compounds.7... 

The migration of borane from the phosphorus atom in 1,3,2,5-dioxa-boraphosphorinane to the phosphorus atom in 1,5,3,7-diazadiphospha-cyclooctane is evidence of a lower phosphorus nucleophilicity in the P(III)—C—O—B(III) system than in the P—C—N fragment, which may result from the phosphorus-boron interaction in 1,3,2,5-dioxaboraphosph-orinane (90IZV1120). 

The mechanism of the reaction is understood to involve direct attack of the phosphorus nucleophile on the electrophilic substrate generating the new C-P bond, as shown in Equation 3.7.144145... 

An unusual approach toward the preparation of a-bisphospho-nates began by treatment of an oxime with a phosphorus nucleophile (trialkyl or dialkyl phosphite) and phosphorus oxychloride (as promoter).354 The oxime undergoes a Beckman rearrangement the phosphorus nucleophile attacks the intermediate cation leading to an imine, which is then further attacked by the phosphorus nucleophile to give the a-bisphosphonate (Equation 3.21). 

Treatment of propyne iminium triflate 258 with silylated phosphorus nucleophiles such as Me3SiPPhR affords (3-morpholinoallenyl)phosphanes 259 in high yield (Scheme 8.69) [150]. 

Compared with the variety of existing carbon or nitrogen nucleophiles that were subjected to nucleophilic addition to there are few examples for phosphorus nucleophiles. Neutral trialkylphosphines turn out to be to less reactive for an effective addihon to Cjq even at elevated temperatures [114], Trialkylphosphine oxides show an increased reactivity. They form stable fullerene-substituted phosphine oxides [115] it is not yet clear if the reaction proceeds via a nucleophilic mechanism or a cycloaddition mechanism. Phosphine oxide addition takes place in refluxing toluene [115], At room temperature the charge-transfer complexes of with phosphine oxides such as tri-n-octylphosphine oxide or tri-n-butylphosphine oxide are verifiable and stable in soluhon [116],... 

Treatment of Cjq with lithiated secondary phosphine boranes or phosphinite boranes followed by removal of the BHj group afforded 1,2-hydrophosphorylated 27 in good yields (Scheme 3.14) [114, 117]. The phosphorus nucleophiles were generated by deprotonation of the corresponding borane complexes with Bull in THF-HMPA, and added to toluene solutions of Cjq at -78 °C. Complexes 26 are stable in air at room temperature for months. In the NMR spectrum, the proton of 26b appears... 

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