Bis-ylide

Benzoxepin (4) was obtained in 55% yield by the reaction of phthalaldehyde with the bis-ylide generated from the bis(triphenylphosphonium) salt prepared from bis(bromomethyl) ether and triphenylphosphane.93,94... 

Treatment of the bis-ylide generated from bis 2-[(triphenylphosphonio)methyl]phenyl ether and sodium amide with oxygen gives dibenz[A./]oxepin (3) in 50% yield.98 99... 

With a-monosubstituted ylides the oxidation results in the formation of alkenes (by subsequent Wittig reaction on the intermediate aldehyde). A recent example of such synthesis is found in the preparation of all-(Z)-cyclododecate-traene by oxidation of the appropriate bis-ylide [33]. It must be pointed out that an approach of the same macrocycle based on ring closing metathesis was found ineffective. 

The reaction of the stabilized yUde 46 (a-vinyl substituted) with the cycloocta-dienyl Pd(II) allows the synthesis of a novel complex, the (rj -allyl)palladium 47, in which the olefmic double bond participates in the coordination (Scheme 20) [83]. The coordination of the bis-yUde 48 with the same starting Cl2Pd(COD) leads to the formation of another new palladium complex 49 via COD exchange reactions. A C-coordination mode takes place between the carbanionic centers of the bis-ylide and the soft palladium and two stereogenic centers of the same configuration are thus created [83]. In contrast to the example described in Scheme 19, the Cl2M(COD) (M=Pd or Pt), in presence of a slightly different car-... 

The bis-phosphonium salt 56 in presence of Pd(OAc)2 leads to the formation of the neutral bis-ylide 57 which reacts with TICIO4 to give the dinuclear cationic complex 58 (Scheme 22) [89,90]. The bis-ylide part, which has potentially two carbons and one oxygen donor atoms, acts as a C,C-chelating ligand through its two soft ylidic carbons. 

It is interesting to notice that the complex 58 is also able to react with soft donor hgands such as triphenylphosphine resulting in the formation in very mild conditions of the unexpected orthometallated complex 59 (Scheme 23) [89,91, 92]. The ligand here is linked to the metal through both an aromatic and an ylidic carbon. Other transformations are realized from 58 leading, including the compounds of the previous scheme, to four different structures for the bis-ylide (i) C,C-chelate (ii) C,C-orthometallated (iii) C,C-orthometallated and free ylide (iv) C,C,C-terdentate (Scheme 23). 

The compound 70 has also been reported showing the ambident character (both C- and N-coordination) of the cyano-stabilized ylide as ligand. The authors have also transposed their work concerning the keto-bis-ylide and palladium, with the synthesis of the C-bonded complex 71 or the new cycloplatinated or-thometallated compound 72. The latter by various treatments allows one to obtain other ylidic cationic complexes of platinum such as 73. A C,C,C-terdentate coordination of the keto bis-ylide, already observed with the palladium is also obtained from the reaction of 73 with gold derivatives. 

A related dinuclear species 77, recently described, constitutes the first dinuclear gold(I) complex with heterobridged phosphor-1,1 -dithiolato moieties and bis(ylide) bridging ligands [ 102]. It is obtained by reaction between [ AuS2PPh2] and the diylide gold complex 74 (R=Me). No intermolecular Au-Au interaction is observed in 77 but the oxidative addition of chlorine to the product leads to a new complex 78 in which a single bond is formed between the two Au(II) centers (Scheme 26). 

The investigations included donor adducts with PO [93], 34,PS [+) [94], 35, and P(NMes ) +) [95], 36. While 34 was only formulated as an intermediate species, the other donor-acceptor complexes, 35 and 36, were characterized by X-ray investigations. To complete this series it may also be compared with bis(ylide)-substituted phosphonium halides [96], 37. For these cases the donors refer to... 

The intramolecular approach of Staab and Graf, shown in Scheme 4, precluded formation of 5, but was considerably more involved [12]. The cyclic dienyne 6 was afforded by Wittig reaction of o-phthaldialdehyde with the corresponding bis(ylide) derived from tolane. Bromination of 6 and subsequent treat-... 

The formation of the naphthalene (73) from the bis-ylide (72) and diethyl ketomalonate involves an unusual olefin synthesis on the carbonyl of an ester group. The methylene-pyrans (75) were formed when the diethyl malonates (74) were refluxed with j3-keto-ylides in xylene or decalin. Possible intermediates are the ketens (76) and the allenes (77). Addition of ylide to the allenes gives the betaines (78) which form methylene-pyrans either directly or via acetylenes as shown. 

B. Macrocyclics. Full details have appeared of the synthesis of the bicyclo[6,2,0]decapentaene (152). Benzocyclobutanedione and the bis-ylide (153) gave only acyclic compounds. The dibenzocyclononatetraene (155) has been obtained from the dialdehyde (151) and the bis-ylide (154). 

Cyclopentene, cyclohexene, and cycloheptene were obtained by intramolecular oxidative couplings of the bis-ylides (161 n = 3, 4, or 5) but oxidation of (161 n = 2) gave cyclo-octa-1,5-diene. Oxidation of the bis-ylide (161 n — 8) gave cyclic polyenes containing 20, 30, 40, 50, and 60 atoms. 

Table 3.14 shows all the known dinuclear gold(II) complexes containing the AU2" core. As happened in gold(II) chemistry the most abundant are those containing a double bridge of the bis ylide CH2PPh2CH2. The first derivative [(C6F5)Au... 

Other heteropolynuclear gold(II) complex that can be obtained by replacement of halide groups in bis(ylide)gold(II) species by other anionic nucleophilic metal complex is the tin derivative [Au2 Sn[N(p-Tol)SiMe2]3SiMe 2 M-(CH2)2PPh2 2] (350).2041... 

Bis-ylides (Scheme 31) may function as four-electron donors and become geminally diaurated. The donor capacity of ylides is generally higher than that of most other ligands, and even powerful donors like tertiary phosphines can thus be readily replaced by non-stabilized ylides. Ylides may therefore be used as auxiliary ligands which are retained, while other components of the coordination sphere are subject to substitution. 

The phosphoranylidene ylide (5) has been obtained as shown in Scheme 2. When fluoride ion is exchanged by chloride ion and the compound heated to its melting point with sodium hydride, hydrogen is evolved and the bis-ylide (6) is distilled from the reaction mixture.9... 

Non-Benzenoid Aromatic Compounds.—The synthesis of aromatic molecules containing small, medium, and large rings, using the reaction of dicarbonyl compounds and bis-ylides, has been thoroughly reviewed.95... 

The interesting hydrocarbon (104), having both aromatic and anti-aromatic character, could be isolated in low yield by treatment of a bis-ylide with freshly distilled glyoxal.96 Precursors for the preparation of helicenes, e.g. (105), have been synthesized in one-step reactions. The yield of the double Wittig reaction is better using a di-aldehyde rather than a bisphosphonium salt.97 The [12]-annulene (106) is obtained from the reaction of the bis-ylide derived from (107) and a di-aldehyde.98 The condensation of (107) with two moles of 3-methylpent-2-en-4-yn-l-al (108) was also successful.99... 

The formation of the heterocycle 1 from the xylylene-bis-phosphonium salt 2 and PCI3 proceeds via a detectable intermediate 3 in a cascade of condensation reactions that is terminated by spontaneous heterolysis of the last remaining P-Cl bond in a cyclic bis-ylide-substituted chlorophosphine formed (Scheme 1) [15]. The reaction scheme is applicable to an arsenic analogue of 1 [15] and to bis-phosphonio-benzophospholides with different triaryl-, aryl-alkyl- and aryl-vinyl-phosphonio groups [16, 18, 19], but failed for trialkylphosphonio-substituted cations here, insufficient acidity prohibited obviously quantitative deprotonation of the phosphonium salts, and only mixtures of products with unreacted starting materials were obtained [19]. The cations were isolated as chloride or bromide salts, but conversion of the anions by complexation with Lewis-acids or metathesis was easily feasible [16, 18, 19] and even salts with organometallic anions ([Co(CO)4] , [CpM(CO)3] (M=Mo, W) were accessible [20]. 

These reactions involve the intermediacy of a bis-ylide which undergoes a Wittig-type reaction with aldehydes or a Michael 1,4-addition to the enone. 

Moreover, if R is an aryl or t-butyl group, by warming at room temperature after the treatment with LDA at -78°C, triacyl-substituted cyclopropanes are formed via a Michael addition involving the intermediates bis-ylide and bis-acylethylene. ... 

Scheme 22 Different ways to promote orthometallation on Pd(bis-ylide) complexes...

Scheme 25 Different strategies to build bis-ylide skeletons...

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