Intramolecular, addition Wittig reaction

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-... 

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 reactivity of the intramolecularly coordinated silenes 929, 934, and 935 has been investigated. The hydrolysis and methanolysis of 929 proceed via formation of Si-O bonds and yield the products 936 and 937 (Scheme 132). The reaction of 929 with benzaldehyde can be regarded as sila-Wittig reaction, and proceeds via the initial formation of the cycloaddition product 938, which rearranges into the cyclodisiloxane [R(Me3Si)SiO]2 939 (R = 8-dimethylamino-naphthyl-l-yl) and l,l-bis(trimethylsilyl)-2-phenylethene 940 (Scheme 132). Methyl iodide catalyzes the isomerization of 929, which proceeds via addition to the Si-C... 

Diels-Alder addition of the benzazete (168) to tetraphenylcyclopentadienone (169) followed by CO loss yields the pentaphenylbenzazocine (170) (75JCS(PI)45). Intramolecular Wittig reaction of (171) gives some 3,4-dihydro-27/-benzoxocin (74JOC3038). 

Diarylpyrroles have been constructed from a-amidonitriles and vinylphosphonium salts. The reaction presumably proceeds by nucleophilic addition to the vinylphosphonium salt followed by cyclization via an intramolecular Wittig reaction. Elimination of HCN accounts for the final aromatization (equation 118) (81JOC2570). 

Acyloins undergo nucleophilic addition to /3-ethoxyvinylphosphonium salts (141) to yield an ylide (142) (74JOC584). Intramolecular Wittig reaction results in formation of the dihydrofuran (143), which is converted to the furan (144) by elimination of ethanol (Scheme 32). Symmetric acyloins give one product, but unsymmetrical ones may give two products under basic conditions due to tautomerization. 

Now the first conjugate addition, an intramolecular reaction between the nitroalkane and unsaturated ester in 92 is followed by conjugate addition of some aryl metal derivative to the unsaturated nitro-compound 93. Both the unsaturated nitro-compound and ester could be made by aldol or Wittig reactions but there is clearly a potential selectivity problem. 

Reaction with N-protected 2-hydroxypyrrolidines or -piperidines. The Wittig reaction with these substrates provides a-alkylated pyrrolidines or piperidines after base-catalyzed intramolecular Michael addition.1... 

Very likely the ammonium fluorides are the proton sources and therefore the reason for incomplete conversions, since potassium fluoride in acetonitrile gives high yields in a very elegant [3 + 2]-annuIation process 87). It combines a Michael addition to a vinyl phosphonium salt with an intramolecular Wittig reaction and proceeds only in the presence of 18-crown-6 with satisfying yield. This cyclopentene synthesis has been executed in a repetitive manner to prepare linear triquinanes as illustrated in Scheme 6. Unfortunately, the sequence is non-stereoselective with regard to the ethoxycarbonyl functions. 

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