Cyanomethylenetriphenylphosphorane

[16640-68-9]  · C20H16NP  · Cyanomethylenetriphenylphosphorane  · (MW 301.33)

(phosphonium ylide, Wittig reagent)

Physical Data: mp 196-197 °C;1 IR;1 UV;2 1H NMR;3 31P NMR;4 pKa;4 rate of hydrolysis.2

Preparative Methods: may be generated by deprotonation of the corresponding phosphonium salt,5,6 by cyanation of Methylenetriphenylphosphorane with p-tolyl cyanate,1 or by the reaction of Acrylonitrile with (Methoxycarbonylmethylene)triphenylphosphorane (eq 1).7

Wittig Reactions.

Cyanomethylenetriphenylphosphorane, as a stabilized phosphonium ylide, has been reacted in Wittig reactions with a great variety of carbonyl compounds to give a,b-unsaturated nitriles with predominantly or exclusively (E) configuration at the newly formed alkenic bond (eq 2) (examples,1,8-15 special application to carbohydrates16-20). Besides aldehydes and ketones, activated esters,21,22 anhydrides,23,24 and imides25 have been used as carbonyl reactants.

A Wittig-type reaction is also involved if cyanomethylenetriphenylphosphorane is cleaved with elemental sulfur26 or selenium.27,28 The thio- or selenoaldehyde intermediate reacts with a second molecule of ylide to give 1,2-dicyanoethylene (eq 3).

Reactions with Other Electrophiles.

Various electrophilic compounds have been reacted with cyanomethylenetriphenylphosphorane, affording (in most cases) substituted derivatives of the original ylide, which can then be used in typical ylide reactions (eqs 4-11).

Borane is added with formation of an alkylidenetriphenylphosphorane-borane which, in contrast to analogous compounds, does not rearrange to the triphenylphosphane-monoalkylborane adduct (eq 4).29 Halogenation may be achieved by using t-Butyl Hypochlorite or elemental Bromine or Iodine, respectively (eq 5).30 The attack of alkylating reagents can occur at the ylide C-atom as well as at the N-atom (eq 6).1 The reaction with acylaziridines yields 3-pyrrolines, which result from intramolecular Wittig reaction of an initially formed cyano ylide (eq 7).31,32 The reaction with acid chlorides leads to the formation of 1-acyl-1-cyano ylides,33-35 which can be pyrolyzed to give 1-cyanoalkynes (eq 8). In the presence of both an aldehyde and an acid chloride, the cyano ylide reacts preferentially at the acid chloride.35 Isocyanates yield 1-cyano-1-carbamoylmethylenetriphenylphosphoranes (eq 9)5,36 and the reaction with Carbon Disulfide followed by an S-alkylation leads to the formation of 1-cyano-1-dithio carboxylic derivatives (eq 10).37 Addition of alkyne carboxylic esters to cyanomethylenetriphenylphosphorane yields 1-alkoxycarbonyl-1-(2-cyanoalkenyl) ylides, presumably via electrocyclic ring opening of an intermediate phosphacyclobutene (eq 11).38

Cyanomethylenetriphenylphosphorane may be deprotonated to give the corresponding ylide anion.39-41 This reacts with electrophiles to give a wide variety of 1-substituted cyano ylides, from which various nitriles are available via Wittig reaction or thermolysis (eq 12).39,40 Reaction with aliphatic aldehydes followed by addition of Chlorotrimethylsilane leads to the formation of 1-cyano-1-alkenyl ylides (eq 13), which are useful synthons for 2-cyano-1,3-dienes. Ring opening of epoxides by the ylide anion provides a route to g-hydroxynitriles, g-butyrolactones, or a-methylene-g-butyrolactones, depending on the subsequent treatment of the initially formed adduct (eq 13).40


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Hans Jürgen Bestmann & Reiner Zimmermann

University Erlangen-Nürnberg, Germany



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