Reactions with phosphorus ylides

Schlosser, M., Christmann, K. F., Piskala, A. Olefinatlon reactions with phosphorus ylides. II. P-Oxido phosphorus ylides in the presence and absence of soluble alkaline metal salts. Chem. Ber. 1970, 103, 2814-2820. 

Reaction with phosphorus ylides the Wittig reaction... 

A dinuclear Pt complex with chelating tris( -tolyl)phosphine and bridging chloro ligands has been converted into a neutral PPhs-coordinated complex 548 and then into cationic complexes containing phosphonium-substituted enolate ligands (549, Scheme 76). Reaction with phosphorus ylides produces 550 and 551. 

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.)... 

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... 

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. 

Reactions of Phosphorus Ylides with Carbon Disulfide, Stable Thiocarbonyl Compounds, and Thiosilanones... 

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... 

As mentioned above (see Scheme 1), three main directions of the decomposition of intermediates that formed are possible when phosphorus and arsenic ylides react with compounds bearing C=X bonds 5,6,19,63,64,88 (i) elimination of R3E15=X to form olefins (Wittig type reaction) (ii) retro-Wittig type decomposition and (iii) elimination of R3E15 and formation of three-membered cycles (Corey-Chaykovsky type reaction). According to the data of Erker and coworkers,12,13,51 under kinetic control, the reaction of phosphorus ylides with thiocarbonyl compounds also affords phosphines and thiiranes, whose further transformations lead to olefins and R3PS under thermodynamic control. 

The intermediate formation of betaines and their subsequent irreversible isomerization to silylated phosphorus ylides have previously been postulated for the reactions of phosphorus ylides with hexamethylsilirane,107 sila-108 and disilacyclobutanes109 with different substituents at the silicon atom (Schemes 34 and 35). 

We theoretically studied the reactions of stable West silylenes 32 and 73 with phosphorus ylide H2C=PMe3.74 Similarly to the simplest analogs of carbenes, these compounds can form betaines in which the negative charge is localized on the silicon atom and the positive charge is localized on the phosphorus atom. These betaines can thermally decompose to form silenes (direction A, Scheme 39) or be isomerized to ylides via direction B. 

As well as the Bingel reaction and its modifications some more reactions that involve the addition-elimination mechanism have been discovered. 1,2-Methano-[60]fullerenes are obtainable in good yields by reaction with phosphorus- [44] or sulfur-ylides [45,46] or by fluorine-ion-mediated reaction with silylated nucleophiles [47]. The reaction with ylides requires stabilized sulfur or phosphorus ylides (Scheme 3.9). As well as representing a new route to l,2-methano[60]fullerenes, the synthesis of methanofullerenes with a formyl group at the bridgehead-carbon is possible. This formyl-group can be easily transformed into imines with various aromatic amines. 

The second class of benzo-fused heterocycles accessible from benzofuroxans are benzimidazole oxides. In this case only one carbon from the co-reactant is incorporated in the product. With primary nitroalkanes 2-substituted l-hydroxybenzimidazole-3-oxides (46) are formed via displacement of nitrite, and / -sulfones behave similarly. The nitrile group of a-cyanoacetamides is likewise eliminated to alford 2-amide derivatives (46 R = CONRjX and the corresponding esters are formed in addition to the expected quinoxaline dioxides from acetoacetate esters. Under similar conditions secondary nitroalkyl compounds afford 2,2-disubstituted 2//-benzimidazole-1,3-dioxides (47). Benzimidazoles can also result from reaction of benzofuroxans with phosphorus ylides <86T3631>, nitrones (85H(23)1625>, and diazo compounds <75TL3577>. 

With no major research on the reaction of phosphorus ylides and aliphatic or alicyclic thiones prior to their investigation, Krapcho et where able to elaborate a useful method for the synthesis of the thietane ring system in addition to the preparation of novel types of thiocarbonyl stabilized ylides (Eq. 1). 

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. 

Reactions with sulfur ylides proceed differently. The products are oxacyclo-propanes (oxiranes) —not alkenes. The addition step proceeds as with the phosphorus ylides, but the negatively charged oxygen of the dipolar adduct then displaces the sulfonium group as a neutral sulfide. This is an intramolecular Sn2 reaction similar to the formation of oxacyclopropanes from vicinal chloroalcohols (Section 15-11C) ... 

The reaction of phosphorus ylides with elemental sulfur gave thioaldehydes, which were trapped in situ by treatment with secondary amines to afford the corresponding thioamides (equation 17)237. 

Benzopentathiepin 27 reacts with phosphorus ylides d-RCgPLtCP PPhjCl (R = MeO, Me, H, Cl, NO2) to form a mixture of benzotetrathiepins 28 and benzotrithiins 29 (Equation 3). The carbanion fragment of the phosphorus ylides replaced the one or two sulfur atoms in the multi-sulfur linkages of benzopentathiepin. Systematic desulfurization to form a new cyclic system was accomplished by the use of a combination of phosphorus ylide and triphenylphosphine in the reactions of benzopentathiepin, benzotetrathiepins, and benzotrithiins <1997H(44)187>. 

The reaction of aldehydes or ketones with phosphorus ylides produces alkenes of unambiguous double-bond locations. Phosphorous ylides are prepared by reacting a phosphine with an alkyl halide, followed by treatment with a base. Ylides have positive and negative charges on adjacent atoms. 

With phosphorus ylides as used for the Wittig Reaction, the phosphorus atom forms a strong double bond with oxygen. This leads the mechanism in a different direction, to effect olefination instead of epoxidation through intermediate oxaphosphetanes. 

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