Wittig reactions intramolecular

M4604>. The synthesis of a fullerene embedded with a furan motif was reported, which was confirmed by a single crystal X-ray analysis <07OL1741>. Tandem Wittig reaction-intramolecular Diels-Alder cycloaddition of 2-furfural provided tricyclic furans, which may serve as precursors in the synthesis of furanosesquiterpenes <07TL3517>. 

The same strategy was applied to reach hyacinthacine A2 (14% overall yield, five steps from 85), with the suitable aldehyde function in 91 being installed via a Wittig reaction. Intramolecular reductive amination finally led to the formation of the pyrrolizidine skeleton of 7 (Scheme 19) [26]. 

Aromatic Substitution (Carey Sundberg, Chapter 11) Intramolecular Wittig Reaction Sigmatropic Rearrangements... 

Some straightforward, efficient cyclopentanellation procedures were developed recently. Addition of a malonic ester anion to a cyclopropane-1,1-dicarboxylic ester followed by a Dieckmann condensation (S. Danishefsky, 1974) or addition of iJ-ketoester anions to a (l-phenylthiocyclopropyl)phosphonium cation followed by intramolecular Wittig reaction (J.P, Marino. 1975) produced cyclopentanones. Another procedure starts with a (2 + 21-cycloaddition of dichloroketene to alkenes followed by regioselective ring expansion with diazomethane. The resulting 2,2-dichlorocyclopentanones can be converted to a large variety of cyclopentane derivatives (A.E. Greene. 1979 J.-P. Deprds, 1980). 

The use of a vinylphosphonium salt as the source of the QQ fragment instead of the more commonly employed 1,2-dicarbonyl substrate is illustrated by the pyrrole synthesis in Scheme 79b (8UOC2570). A particularly interesting feature is the intramolecular Wittig reaction with an amide carbonyl group. A very useful synthesis of pyrroles depends upon the addition of the anion of p-toluenesulfonylmethyl isocyanide (TOSMIC) to a,/3-unsatur-... 

Intramolecular Wittig reaction of [2-hydroxy-3-(2-formylphenoxy)propyl]triphenylphos-phonium bromide with sodium ethoxide gives 1-benzoxepin (2) as minor product only (5%) and 2-(allyloxy)benzaldehyde (40%).96... 

Phenylcyclopent[c]azcpine (33a) and 6,7-fused cyclopentazepines 33b-d are formed in moderate yields in a one-pot, two-stage process involving initial condensation of triphenyl-[(l-phenylvinyl)imino]phosphoranes 32 with 6-(dimethylamino)fulvene-2-carbaldehyde (30), followed by an intramolecular aza-Wittig reaction of the iminophosphorane with the pendant aldehyde function.5 The method fails with the unsubstituted vinylphosphorane 32 (R1 = R2 = H). 

Two intramolecular aza-Wittig reactions leading to 1,3-benzoxazepines have been described. In the first,19 ethyl (Z)-3-(2-acyloxyphenyl)-2-azidoprop-2-enoates 1 are treated with triphenyl-phosphane under argon at 20°C for 3-4 hours when 2-substituted ethyl 1,3-benzoxazepine-4-carboxylates 2 are obtained in 85-90% yield. 

Alkoxy-3//-l,4-benzodiazepin-5(4//)-ones by Intramolecular Aza-Wittig Reactions... 

An intramolecular aza-Wittig reaction of the imino-A5-phosphancs 4, prepared by the action of triphenylphosphane on the corresponding azido compounds, affords l//-l,2,4-benzo-triazepines 5.346 The reactions were carried out by heating compounds 4 in acetonitrile or 2-hydroxyethyl methyl ether for the time indicated. No further details were reported. 

Heterocyclic sulphoxides 65 mass spectra of 130-132 Hexahydronaphthalenols, synthesis of 310 Hofmann elimination 953 HOMO energies 1048, 1049 Homolytic substitution 1109 intramolecular 846 Horner-Wittig reaction 333 Hot electrons 892, 893 HSAB theory 282, 549 Hydrides, as reducing agents 934-941, 959 Hydrogen abstraction, photochemical 874, 876, 877, 879, 880... 

The Wittig reaction has been carried out intramolecularly, to prepare rings containing from 5 to 16 carbons, both by single ring closure... 

The 5,8-dimethoxy-2(l//)-quinolinones 60 were obtained in moderate yield via an intramolecular Wittig reaction <95LA1895>. 

The synthesis of pyrrolo[3,4-c]pyridazines 20 is achieved by intramolecular aza-Wittig reactions of the phosphazines 19 <95JHC1457>. 

Triphenylphosphine gives Michael additions to the activated triple bond of acetylene dicarboxylic esters in presence of acidic compounds HY (Scheme 1). The reactions take place easily at room temperature, even at -10°C [1], through formation of intermediate activated vinylic phosphonium salts, which undergo a subsequent Michael addition of HY. The reactions afford various stabilized ylides which can be isolated in high yields or undergo possibly evolution, for example by intramolecular Wittig reaction [2]. 

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 Horner-Wittig reaction of a-phosphoryl sulphoxides 442, which are chemically stable, results in the formation of a, -unsaturated sulphoxides 443 in high yields (equation 264). The reaction has been found to be non-stereoselective, mixtures of E and Z isomers being formed from aldehydes and unsymmetrical ketones . In the case of aromatic aldehydes this reaction can also be advantageously performed in a two-phase catalytic system even without the usual PTC catalysts (Table 24). Intramolecular Horner-Wittig reaction of a-phosphoryl-5-oxosulphoxides 444 leads to a, -unsaturated cyclic sulphoxides 445 (equation 265). Starting from optically active 0,0-... 

The following example completes the section of threefold anionic domino processes initiated by a SN-type reaction. As discussed earlier in Section 2.2, the reaction of a five-membered cyclic phosphonium ylide with enones, a, 3-unsaturated esters, and a, 3-unsaturated thioesters provides cycloheptene or hydroazulene derivatives in a domino Michael/intramolecular Wittig reaction. This sequence... 

A solvent-free synthesis of benzo[b]furan derivatives 10-79, a class of compounds which is often found in physiologically active natural products, was described by Shanthan Rao and coworkers. These authors heated phosphorane 10-71 for 8 min in a microwave oven and obtained the benzo[b]furan 10-74 in 73% yield (Scheme 10.18) [25]. The sequence is initiated by an intramolecular Wittig reaction, providing alkyne 10-72 this underwent a subsequent Claisen rearrangement to give the intermediate 10-73. Also in this case, normal oil-bath heating gave much lower yields (5%) of the desired product the authors hypothesize that the micro-... 

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