Benzaldehyde Wittig reactions

The work of Hyatt on cyclotriveratrylene—derived octopus molecules contrasts with this. Of course, these species have the advantage of ligand directionality absent in the benzene-derived octopus molecules. Except for the shortest-armed of the species (i.e., n = 1), all of the complexing agents (i.e., n = 2—4) were capable of complexing alkali metal cations. Synthesis of these species was accomplished as indicated below in Eq. (7.7). These variations of the original octopus molecules were also shown to catalyze the reaction between benzyl chloride and potassium acetate in acetonitrile solution and to effect the Wittig reaction between benzaldehyde and benzyltriphenylphos-phonium chloride. 

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... 

Recently, water-soluble phosphonium salts were synthesized and their Wittig reactions with substituted benzaldehydes were carried out in aqueous sodium hydroxide solution (Eq. 8.114).309... 

Reaction of the tri- -butylphosphine adduct 180 with compound 157 leads to cycloaddition across the two sulfur atoms to give corresponding 2-tri- -butylphosphoranylidene-l,3-dithiole 181, which can be trapped by in situ Wittig reaction with benzaldehyde to give 182 (Scheme 21) <1994CC2603, 1997T2261>. 

Aminoethylidenehydrazones 161 react with triphenyl phosphine to give the azinoiminophosphorane intermediates 162 which cyclize via an aza-Wittig reaction with benzaldehydes to give the corresponding 1,2,4-triazoles 163a-j (Scheme 14 and Table 32) <2002JHC845>. 

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... 

Two hindered phosphoranylidenephosphines, ArP=PMc3 [76 Ar = 2,6-dimesityl-phenyl and 2,4,6-tri(r-butyl)phenyl], have been prepared and are stable in the absence of air and water. As the resonance suggests, they can enter into phospha-Wittig reactions to produce phosphaalkenes (77). The reaction gave high yields of ( )-(77) in a few hours for a range of benzaldehydes (p-Cl/N02/0Me/NMe2/H, F5), and also for ferrocenecarboxaldehyde and pivaldehyde, but was unsuccessful for ketones. 

Oxaziridines (80) are obtained by an aza-Wittig reaction of benzaldehyde 77 and A-Boc-triphenyliminophosphorane 78 and subsequent ozonolysis of the imine 79, as shown in Scheme 40 (93JOC4791). 

After these results had established the feasibility of generating and utilizing a carbohydrate phosphorane, the two systems that had been reported earlier were examined in order to determine if similar conditions would allow them to undergo the Wittig reaction. The ylide derived from phosphonium salt I condensed with both benz-aldehyde and U-chlorobenzaldehyde to produce good yields of olefinic products Villa and Vlllb. The ylide derived from phosphonium salt II also was successfully condensed with benzaldehyde, but the yield of IX was only 30 , presumably because of its extremely poor solubility even in an HMPA-THF solvent mixture. Both of these systems supported the tenet that it was possible to use unstabilized carbohydrate phosphoranes if the conditions are proper and if the g-oxygen is attached to the carbohydrate through another set of bonds. 

The 4-hydroxy-3-(3-methyl-3-buten-l-ynyl)benzaldehyde, 250, a phytotoxic compound responsible for vineyard die-back, has been [14C]-labelled263 via Wittig reaction using [14C]CH3l as precursor (equation 137). 

Carbonyl KIE in the Wittig reaction of benzaldehydes with benzylidenetriph-enyiphosphoranes... 

Carbonyl-uCKIE in the Wittig reaction of non-stabilizedylides with benzaldehyde and benzophenone... 

Electrochemical generation of strong base has been applied in an interesting modification of the Wittig reaction 161 A solution of azobenzene, benzaldehyde, benzyltriphenylphosphonium bromide, and lithium chloride in dimethylformamide was electrolyzed at a potential where only the easily reducible azobenzene was electroactive. The phosphonium ion then acts as a proton source, giving the ylide as an intermediate. Under these conditions a 98 % yield of a mixture of cis- and trans-stilbene was obtained, presumably via the following reactions ... 

Naturally occurring 6-prenylcoumarins have been synthesised from 2-prenyloxy-benzaldehydes through tandem Wittig reaction and Claisen rearrangement. Several of the... 

In this scheme, the intermediate alcohol results from hydroboration of a double bond that is introduced by a Wittig reaction between benzaldehyde and methylenetriphenylphosphorane. 

The trisubstituted double bond suggests a Wittig reaction. Reaction of cyclopentanone with the Wittig reagent formed from benzyl bromide (formed from benzaldehyde in (a)) yields the desired product. 

Although phosphorus ylids are most commonly used to alkenylation reactions, nitrogen ylids can occasionally be used. As an example, the reaction of A-benzyl-A-phenylpiperidinium bromide with base generated a N-ylid, which reacted with benzaldehyde to form styrene. The stmcture has been determined for an intermediate in an aza-Wittig reaction. 

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