2-nitrobenzyl triphenylphosphonium

P 59] A third protocol differed from [P 57] and [P 58] by sequential insertion of all reactants instead of using a pre-mixed solution of nitrobenzyltriphenyl-phosphonium bromide and sodium methoxide. As above, flow was fed by electroosmotic means [13]. A 40 pi volume of a methanol solution of 0.01 M 2-nitrobenzyl-triphenylphosphonium bromide was filled into the first reservoir, 40 pi of a methanol solution of 0.015 M sodium methoxide in the second, 40 pi of a methanol solution... 

OS 78] [R 4a] [P 58] The Wittig reactions of five aldehydes with 2-nitrobenzyl-triphenylphosphonium bromide were investigated also at a 1 1 stoichiometric ratio [13]. Using optimized reaction conditions, improved yields were found for four of the five aldehydes. 

Acid- and base-promoted methods have also been used in the syntheses of pyrazoles. Hydrogenation of methyl 2-Cbz(hydrazine)-3-hydroxy-4,4-dimethoxybutanoate 11 followed by cyclization in the presence of trifluoroacetic acid afforded the first asymmetric synthesis of the (4S,5.R)-5-carbomethoxy-4-hydroxy-A2-pyrazoline 12 <00TL8795>. Reaction of 2-nitrobenzyl triphenylphosphonium ylide (13) with aiyl isocyanates afforded 2-aryl-2H-indazoles 14 <00TL9893>. Base-promoted reaction of nitrobenzenes 15 with aryl imines 16 afforded aryl pyrazoles 17 . 

Reaction of 2-nitrobenzyl triphenylphosphonium ylide 205 with aryl isocyanates affords 2-aryl-2//-indazoles 206 (Scheme 122) <2000TL9893>. 

Reaction of 2-nitrobenzyl triphenylphosphonium ylide 745 with aryl isocyanates afforded 2-aryl-2//-indazoles 746 (Equation 159) <2000TL9893>. Reductive cyclization of o-nitroketoximes 747 in the presence of catalytic iron dimer in dioxane under a carbon monoxide atmosphere furnished l//-indazoles 748 (Equation 160) <2004H(63)373>. 

Wittig reactions of phosphonium fluorides in dipolar non-HBD solvents can be carried out without an additional base e.g. 4-nitrobenzaldehyde reacts slowly with (4-nitrobenzyl)triphenylphosphonium fluoride in refluxing acetonitrile to give 4,4 -nitro-stilbene in good yield (84 cmol/mol) [642], In this reaction, the fluoride ion attacks its own cation to give the corresponding Wittig ylide as intermediate. 

Treatment of 8-[(4-cyanophenyl)methoxy]-7-formyl-2-cyclopentyl-2,3,4,6,11,1 la-hexahydro-l//-pyrazino[l,2-i]isoquinoline-l,4-dione with (Et0)2P(0)CH2C00Et and NaH in THF at 40 °C overnight, or with (2-pyridylmethyl)-, 4-[(ethoxycarbonyl)benzyl]-, (4-nitrobenzyl)-, and (meth-oxymethyl)triphenylphosphonium halogenide in the presence of KH in THF at room temperature gave 7-ethylene derivatives 386 (98MIP7). 

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