Phosphorus nucleophiles addition

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). 

In addition there are certain other methods for the preparation such compounds. Upon heating of the thionocarbonate 2 with a trivalent phosphorus compound e.g. trimethyl phosphite, a -elimination reaction takes place to yield the olefin 3. A nucleophilic addition of the phosphorus to sulfur leads to the zwitterionic species 6, which is likely to react to the phosphorus ylide 7 via cyclization and subsequent desulfurization. An alternative pathway for the formation of 7 via a 2-carbena-l,3-dioxolane 8 has been formulated. From the ylide 7 the olefin 3 is formed stereospecifically by a concerted 1,3-dipolar cycloreversion (see 1,3-dipolar cycloaddition), together with the unstable phosphorus compound 9, which decomposes into carbon dioxide and R3P. The latter is finally obtained as R3PS ... 

The initial step of olefin formation is a nucleophilic addition of the negatively polarized ylide carbon center (see the resonance structure 1 above) to the carbonyl carbon center of an aldehyde or ketone. A betain 8 is thus formed, which can cyclize to give the oxaphosphetane 9 as an intermediate. The latter decomposes to yield a trisubstituted phosphine oxide 4—e.g. triphenylphosphine oxide (with R = Ph) and an alkene 3. The driving force for that reaction is the formation of the strong double bond between phosphorus and oxygen ... 

Nucleophilic Addition of Phosphorus Ylides The Wittig Reaction 721... 

ATP is activated by coordination to magnesium ion, and nucleophilic addition of a fatty acid caiboxylate to phosphorus then yields a pentacoordinate intermediate. . ... 

Whereas the nucleophilic addition of vinylmagnesium bromide to a-alkoxy aldehydes (12, 16) proceeds with a low to moderate chelation-controlled diastereoselectivity, a remarkably high preference for the opposite stereochemical behavior is found with the jS-silyl phosphorus ylide 1477. Due to the electron-donating 4-methoxyphenyl substituents at the phosphorus atom, as well as the /i-methyldiphenylsilyl group, 14 is an excellent vinylation reagent which does not lead to any Wittig olefination products. 

We shall discuss first reactions in which hydrogen or a metallic ion (or in one case phosphorus or sulfur) adds to the hetero atom, and then reactions in which carbon adds to the hetero atom. Within each group, the reactions are classified by the nature of the nucleophile. Additions to isocyanides, which are different in character, are treated at the end. 

The iminophosphenium cation was also of interest for more physical investigations. It was noted to be a stable entity in gas phase experiments [52], the parameters were investigated in detail [53] and a systematic study of the nucleophilic addition of CH, NH and OH bonds was performed [54] with a concomitant interpretation of the chemical shifts (at the dicoordinate phosphorus centres). The latter authors also confirmed the loose interaction of a triphenylphosphine with the iminophosphenium cation (PP = 2.625 A). 

A-trityl-(l/ ,2S)-norephedrine (58), the corresponding allyl phosphonates 62a,b were obtained via the Arbusov rearrangement of 2-ethoxy-1,3,2-oxazaphospholidine 60. The absolute configuration of the major diastereomer, 62a was determined by X-ray as (2S1,45,51 ).The reaction of the major diastereomer of allyl phosphonates 61a and 62a with DBU afforded the corresponding vinylphosphonates 63a,b (Scheme 21) [48], Nucleophilic addition to these resulted in induction of chirality at the [1-position of the stereogenic phosphorus atom in the initially produced diastereomeric phosphonates 64 or 65 (Scheme 21) [48],... 

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],... 

The conjugate addition of phosphorus nucleophiles of various oxidation states and in neutral or metallated form constitutes an efficient and well-known method for C—P bond formation [30]. In the case of phosphanes as nucleophiles especially, the corresponding phosphane-borane adducts have been used in 1,4-additions to Michael acceptors. Following the idea to use a chirally modified phosphorus nucleophile in asymmetric Michael additions to aromatic nitroalkenes, we synthesized the new enantiopure phospite 45 starting from TADDOL (44) with nearly quantitative yield. Due to the C2 symmetry, of the... 

CHMe, cyclopropylidene, and CMe2 to activated double bonds.1075 Similar reactions have been performed with phosphorus ylides, 076 with pyridinium ylides,1077 and with the compounds (PhS)3CLi and Me3Si(PhS)2CLi.1078 The reactions with ylides are of course nucleophilic addition. 

The most interesting properties of phosphoranes, i.e. their role as intermediates or transition states of nucleophilic addition reactions of four-coordinate phosphorus compounds and their intramolecular rearrangements according to BPR or TR, have already been fully considered. The synthetic potential of stable phosphoranes has been reviewed by Burger in great detail (B-79MI11702), and only some special aspects need be mentioned in this chapter. 

An additional example utilizing phosphorus nucleophiles employs lithium diphenylthiophosphides and allyl carboxylates and yields allylic diphenylphosphine sulfides (equation 66).2 1... 

The stereochemistry of the Pd-catalyzed reaction of lithium diphenylthiophosphides with allyl acetates was determined using a 5-phenylcyclohex-2-enyl system. This phosphorus nucleophile was found to add exclusively via ligand addition (equation 197).224 386... 

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