Phosphorus betaine

Synthesis of Glycosides Reactions of the Anomeric Hydroxyl Group with Nitrogen-Phosphorus Betaines, W. A. Szarek, H. C. Jarrell, and J. K. N. Jones, Carbohydr. Res., 57 (1977) C13-C16. 

Szarek, W A, Jarrell, H C, Jones, J K N, Synthesis of glycosides reactions of anomeric hydroxyl group with nitrogen-phosphorus betaines, Carbohydr. Res., 57, C13-C16, 1911. 

Ustynyuk and co-workers continue to describe their studies of the structures and reactivities of silicon-containing phosphorus betaines and ylides. In their... 

The zwitterionic phosphorus betaine intermediates from the reaction of conjugated azoalkenes with triphenylphosphine selectively undergo cyclization to four-membered 1,2-oxaphosphetane intermediates. From them 4-unsubstituted-5-alkoxypyrazoles have been obtained through loss of a triphenylphosphine oxide molecule [92T1707]. This behaviour is in full agreement with a typical Wittig reaction (Scheme 10). 

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 ... 

In the Wittig reaction, a phosphorus ylide, R2C—P(C6H03, also called a phosphoreme and sometimes written in the resonance form R2C=P(C6H5)3, adds to an aldehyde or ketone to yield a dipolar intermediate called a betaine. (An ylide—pronounced ill-id—is a neutral, dipolar compound with adjacent plus and minus charges. A betaine—pronounced bay-ta-een—is a neutral, dipolar compound with nonadjacent charges.)... 

The synthesis and surface-active properties of higher hydroxyalkanediphos-phonates are discussed in Ref. 67. Phosphorus-containing betaines as hydrolytically stable surfactants, free from alkali salt impurities, were prepared by a reaction of amidoamines and equimolar amounts of phosphonate esters with 1.5-2 eq of formaldehyde at 60-140°C in a polar solvent [72]. 

Regitz has shown that the reaction of azaphosphole 38 with two equivalents of DEAD furnishes the zwitterionic 2 1 adduct 39 (Scheme 8) [52]. The extreme low frequency shift of the P NMR signal by more than 220 ppm in comparison to that of the azaphosphole confirms the formation of a betaine possessing a hexacoordinated phosphorus atom. 

The reaction of 9 (generated thermally from 7 in toluene) with tetraphenyl-cyclopentadienone is more complex. Both the [6 + 2]-cycloadduct 3416), for which an X-ray structure analysis is available, and the [12 + 2]-cycloadduct 3516), whose constitution has been assigned primarily on the basis of H-NMR evidence, are obtained. The two cycloadducts presumably have a common intermediate which, in accord with the general reactivity of 9, should possess betaine character (.31 - 32) it is caused by nucleophilic attack by the carbonyl oxygen atom on the phosphorus of the heterocumulene. Ring closure of the carbanionic carbon atom... 

Acyclic boryloxyalkylphosphines with tricoordinated phosphorus and boron are capable of forming cyclic betaine structures with four-coordinated P and B atoms. The ability to be converted into a more stable four-coordinated state accounts for many chemical transformations of boryloxyalkylphosphines. Diphenylboryloxymethyl(methyl) phenylphosphine (92) readily disproportionates to give 1,3,2,5-dioxabora-taphosphoniarinane (103). [Eq. (60)] (83IZV2541). Similar interaction is... 

Betaines may be considered to be the intermediate products in the displacement of the C—O fragment from the P—C—O—B system, whereas the addition of aldehydes to the P—C—O—B system constitutes the first stage. This reaction is due to the fact that phosphorus and boron atoms can change their coordination reversibly and convert into the tetra-coordinated state. The displacement of one aldehyde by another is carried out in a solvent or in excess aldehyde. In general this reaction is represented by the following scheme [Eq. (107)]. 

The C—O fragments separating phosphorus and boron atoms in dioxa-borataphosphoniarinanes are substituted when treated by aldehydes or nitriles. In this case the displacement of aldehyde fragments occurs through the initial dissociation of betaines into compounds with Uncoordinated phosphorus and boron atoms [Eq. (109)] (86IZV2502, 86IZV2510). 

The disulfide fragment separating phosphorus and boron atoms was not replaced in 181 by chloral even after refluxing in benzene, evidence for high betaine stability. In methylene chloride, 175 reacts with 1,2-naphthoquinone, yielding phosphorane 182 [Eq. (135)]. This result is surprising, as one could have expected the formation of a betaine structure. 

Organometallic betaines of type I can be considered as the closest structural analogs of carbon betaines of the (+ )P-C-C-X( ) type (IV), which were regarded for a long time as possible intermediates in classical reactions of carbonyl and thiocarbonyl compounds with phosphorus ylides (Wittig and Corey-Chaykovsky reactions and related processes,5,6 Scheme 1). Vedejs and coworkers7,8 proved unambiguously that oxapho-sphetanes (III) are true intermediates in the reactions of nonstabilized phosphorus ylides with carbonyl compounds. The formation of oxabetaines (+)p-c-c-o(-> was detected only in the form of their adducts with lithium salts.9,10... 

It is commonly accepted5,6,19 that unstable betaines IV (X = C) are intermediates of the cyclopropanation of olefins with the polar C=C bond by phosphorus ylides. However, only one compound of this type, viz., Me3P( + )-CH2-CMe2-C5H4( ) (1), synthesized in the reaction of dimethyl-fulvene with methylenetrimethylphosphorane, was isolated and characterized by multinuclear NMR spectroscopy.20... 

The first kinetically stable dibenzosilafulvene (7), whose structure and properties should more correctly be described by the resonance hybrid 7a 7b with a great contribution of the ylide form 7a, reacts with phosphorus ylide to form betaine (8), which is rearranged, under thermodynamically controlled conditions, into the salt (9) (Scheme 4).24,25... 

The double bond in silenes is strongly polarized. They react with phosphorus ylides, as shown by Brook and MacMillan,45 like alkenes with the strongly polar C=C bond. Therefore, it is reasonable to suggest that the reaction also occur through the betaine intermediate (12) (Scheme 6). 

The intermediate formation of betaines with the carbanionic center is also postulated in the reactions of permethylsilirane, sila- and disilacyclobutanes with phosphorus ylides. For data on these betaines isomerized in situ to silylated phosphorus ylides, see Section 5.4. 

The first stable organophosphorus betaines with thiolate centers in the carbon series of the type (13) were prepared by the reaction of phosphorus... 

The first silicon-organophosphorus betaine with a thiolate center (15a) was synthesized by the reaction of stable silanethione (14) with trimethyl-methylenephosphorane (Scheme 8) and characterized by multinuclear NMR spectroscopy.14 Compound 15a is formed under kinetic control and is transformed, under the thermodynamically controlled conditions, into the silaacenaphthene salt (16). The processes presented in this scheme reflect the competition of the basicity and nucleophilicity of phosphorus ylides. Betaine 15b prepared from less nucleophilic and less basic ylide with phenyl substituents at the phosphorus atom is much less resistant toward retro-decomposition compared to the alkyl analog. Its equilibrium concentration does not exceed 6%. 

The spectral parameters of 15a and other silicon-organophosphorus betaines described henceforth in Section 2.2.2 allowed us to show reliably that the reaction of phosphorus ylides with thiocarbonyl compounds, unlike the classical Wittig reaction, occurs through the intermediate formation of betaines (17)11 (Scheme 9). Erker and coworkers performed a more detailed... 

The reaction of 18 and 19 with phosphorus ylides occurs as a stepwise process. Betaine (21) can be isolated when (Me2SiS)3 reacts with Ph3P=CHMe in a 3 2 ratio of the reactants (Scheme 11). This substance is quite stable in the solid state but on dissolving in pyridine it is reversibly transformed into a mixture of 20k and (Me2SiS)3. The equilibrium concentration of 21 in a solution at room temperature is at most 28% according to the NMR data, and the addition of one more equivalent of Ph3P=CHMe to the solution results in the quantitative transformation of 21 into 20k. 

The reactions of dichlorocarbene with phosphorus ylides result in the corresponding olefins and phosphines.66-68 In the reaction of dichlorocarbene generated in situ with tributyl- and triphenylmethylenephosphoranes or triphenylethylidenephosphorane, the olefin yield increases as the nucleo-philicity of phosphorus ylide increases. According to,67 the reaction starts from the electrophilic attack of carbene at the a-C atom of phosphorus ylide. Then the intermediately formed betaine (28) (Scheme 14) decomposes to eliminate the phosphine molecule and form dichloroolefin (29). 

The first organophosphorus betaines ( + )E15-C-E14( ) (31) with the negative charge on the atom of the Group 14 element were prepared by Veith and Huch69 in the reaction of cyclic stannylene (30) with phosphorus ylides (Scheme 15). 

According to the data of Griitzmacher et al., the isomerization of the proposed intermediate betaine 41, which is formed in the reaction of bis[2,4,6-tris(trifluoromethyl)phenyl]stannylene 39 with phosphorus ylide 40, affords stannylene 41 (Scheme 18).76... 

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