From phosphoranes

Phosphazenes were also obtained from phosphoranes, Ph3P=CR2, with a wide range of R substituents including H, Me, C02Me, COPh, p-fluorenyl, and C02(CH2>2C02 . 

The most common method for the generation of the metal alkylidene species seems to be a-elimination from an intermediate dialkyl-metal species. This procedure gives the most active catalysts. Above we mentioned the addition of other carbene precursors, which leads to active catalysts. Other methods to generate the metal alkylidene species involve alkylidene transfer from phosphoranes [16] or ring-opening of cyclopropenes [17], In Chapter 16.4 we will describe a few compounds that are active by themselves as metathesis catalysts. 

Several 2-phenoxychromones have been prepared from phosphorane carbonates (464), the precursors of which are available from o-hydroxypropiophenone (Scheme 170). The action of heat on the ylide causes cyclization to a chromanone derivative, which loses phenoxide when R = H to give the chromandione (465), but loses triphenylphosphine oxide in other instances to give the 2-phenoxychromone (466) (81CC282, 474). 

Another attractive route to the synthesis of highly reactive tungsten carbene complexes involves alkylidene transfer from phosphoranes. Arylimido tungsten... 

A series of interesting derivatives was prepared21,69 starting from phosphoranes having maleimido, amido, and nitryl functions. These products were 2,4 3,5-di-0-benzylidene-l-deoxy-l-(2,5-dioxo-3-pyr-rolylidene)-D-ribitol (99a), its N-phenyl derivative (99b), 2,4-0-benzylidene-1 -deoxy- l-(2,5-dioxo-3-pyrrolylidene)-D-ribitol (99c), 4,6 5,7-di-0-benzylidene-2,3-dideoxy-D-nbo-hept-2-enonamide (100), 2,3-dideoxy-D-giuco-oct-2-enonamide 4,5,6,7,8-pentaacetate (101), 4,6 5,7-di-0 - benzylidene - 2,3 - dideoxy - D - ribo-hept-2-enononitrile (102), and 2,3-dideoxy-D-g(uco-oct-2-enononitrile 4,5,6,7,8-pentaacetate (103). Derivatives 99a-99c were prepared for use in the... 

Olefin synthesis from phosphorane ylides (e g 3) with aldehydes or Ketones c predominate m aliphatic systems trans m conjugated olefins... 

Phosphonic esters from phosphoranes. The facile transformation of phosphoranes... 

Allenic Esters and Dienoates. - The Wittig approach to allenes from phosphoranes and ketenes or equivalents thereof has been... 

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