Phosphoms ylides

Phosphoms ylides in synthesis and transformations of heterocycles 94MI4. 

Heating a-hydroxy amides 135 in xylene with the cumulated phosphoms ylide 134 gives the 2(3//)-oxazolones 140. The reaction proceeds via an addition-cyclization-intermolecular-Wittig olefination sequence, which imphes three different types of phosphorus ylides, 134,136, and 137, respectively, of increasing ylide activity (Fig. 5.33 Table 5.7, Figs. 5.34, 5.35). 

Phosphorus ylides, P=C compounds with a pentavalent phosphorus atom, can give phosphetanes as well as phosphaalkenes. By the reaction of a stabilized phosphoms ylide with activated alkenes, the phosphetane ring is formed via a zwitterionic betaine <1997HAC157>. 

This is an example of the Wittig reaction which occurs when a phosphoms ylide reacts with an aldehyde or a ketone. An ylide is a molecule in which there exists a natural state of charge separation. In this case, the ylide is... 

Also, the colorless selena-A -phosphinidene 8b has been obtained by addition of selenium to a phosphoms ylide (Scheme 13) in THF at room temperature <2002JA9706, 2003BCJ471>. 

The dithiole 108 was treated with tetrafluoroboric acid followed by triphenylphosphine to give the phosphonium salt 117 (Scheme 4) <1996JOC2877>. Treatment with triethylamine gave the phosphoms ylide 109 <1996JOG2877>. 

Keywords ketone, phosphoms ylide, Wittig reaetion, microwave irradiation, olefin... 

Highly stabilized phosphorus ylides are prepared from acetylenic esters, a carbon-based nucleophile, and triphenylphosphine in aqueous media." In acetone-water (2 1) solvent, the reaction proceeds via the conjugate addition of triphenylphosphine to dialkyl acetylenedicarboxy-lates the resulting vinyl triphenylphosphonium salts undergo Michael addition reaction with a carbon-nucleophile to give the corresponding highly stabilized phosphoms ylides. 

Wittig reaction (Section 19.11) The reaction of a phosphoms ylide with a ketone or aldehyde to yield an alkene. 

Looking for the catalytic systems, which may be easily deactivated and removed from the polymer, other nonionic base/alcohol-iiutiating systems have been examined. Phosphoms ylides, R3P = CMe2 (eqn [19]), show the activity similar to phosphazene bases in polymerization of D4. They are thermolabile and easy to remove from the polymer. Promising initiators are also stable (N-hetaryl)carbenes (eqn [20]) and guanidine derivatives. The MWs of the silicone polymers in case of carbenes can be regulated simply by varying the quantity of the alcohol co-initiator. 

The phosphoms-ylides based olefination reactions also find applications to halogenated dienes. For instance, the Homer—Wadsworth—Emmons methodology was successfully applied to (Z)-2-methyl-3-iodo-propenal and led efficiently to the expected y-pyrone-substituted ( ,Z)-1,3-diene (E/Z > 6 1), a key-synthon for a total synthesis of ( )-9,10-deoxytridachi(Mie [204],... 

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