Phosphoranes of Special Interest

The ylide anion (48) reacts with a variety of electrophiles at the terminal carbanion site to form /S-keto-ylides, e.g. (49). 53 64 The reaction between the ylide derived from cyclobutyltriphenylphosphonium bromide and cyclobutanone gave a reasonable yield of bicyclobutylidene (50).68 

Ph3P=CHCOCH3 -52 Ph3P=CHCOCH, cllirH0 Ph3P=CHCOCH2CHOHCH3 

Michael additions occur between (diethoxyvinylidene)triphenylphosphorane and carbonyl compounds which have an a-CHa. The initial products eliminate EtOH to 

The (aziridin-l-ylimino)phosphoranes (57) react with ketens to give nitrile derivatives, presumably from an intermediate ketenimine by breaking the N—N bond and migration of the aziridinyl group.60 They also react with acyl halides and 

Semi-empirical molecular orbital calculations on the phosphorane (96) 

Allyl vinyl ethers have been prepared using the ylide (101) but only from non-enolizable carbonyl compounds. The ethers rearrange on heating to give a-allyl aldehydes, e.g. (102). 

Yoshida, S. Yoneda, Y. Murata, and H. Hashimoto, Tetrahedron Letters, 1971, 1523. Z. Yoshida, S. Yoneda, H. Hashimoto, and Y. Murata, Tetrahedron Letters, 1971 1527. 

Full details have appeared of the generation and use in synthesis of the chlorofluoromethylene-ylide (103). Fluoromethylenetriphenylphosphorane (104) has been prepared as shown and among other unusual ylides used in normal olelin synthesis are (105), (106), (107), (108), and (109). The latter gave acyclic phosphine oxides (110) in up to 50% yield. 

The seven-membered exocyclic phosphorane (111) with the fluorene-aldehyde (112) gave triphenylphosphine and the aldehyde (114) instead of the expected olefin. Compound (114) could have been formed as shown, the phosphorane functioning as a base to generate the anion (113). 

The product obtained from triphenylphosphine and perfluorocyclobutene has been shown by Jif-ray analysis to be the ylide (47). The same technique has 

The fluorenylidenephosphoranes (51), which had not previously been observed to react with ketones, reacted exothermically with the central carbonyls of the triones (52) and (53) to give the corresponding olefins. Photoelectron spectroscopy and X-ray analysis suggest that the phos-phorane (54) has 20% of ylene and 80% of ylide character, in agreement with previous calculations. Phosphorane (54) couples with benzaldehyde in 

The betaines (58) did not react with benzaldehyde even in refluxing DMSO, but with other electrophiles they reacted readily on the central nitrogen.  

Thermolysis of the tungsten-ylide complex (59) in cyclohexene gave the hydrocarbon (60), perhaps via the carbene QO.  

No evidence was found for the phenolic form (62) in the i.r. and n.m.r. spectra of the diphosphacyclohexadienone (61). The triboluminescence of the phosphorane Ph3P=C=PPha has been investigated.  

Cyclic phosphonium ylides have been reviewed. Ab initio calculations on methylenephosphorane, HaC PHg, show no barrier to rotation round the CP bond whether or not d-orbitals are included in the calculations. The energy changes when these orbitals are included are commensurate with p -d feedback. 

Details have appeared of the semi-empirical MO calculations on cyclopentadienylidenetriphenylphosphorane (66). A kinetic investigation of the reaction of this phosphorane with tetracyanoethylene in the presence 

The 3-phospholenium salt (70) with aromatic aldehydes and potassium t-butoxide in THF gave the trienes (71) in low yield, presumably via the intermediate phosphine oxides (72). The unsaturated lactones (74) were 

2-Aminopyridine adds to the j8-acylvinylphosphonium salt (80) to give the salt (81a) or (81b), which has been used successfully in olefin synthesis. The salts (82) with benzaldehyde and ethanolic ethoxide gave the olefins (83), which were isolated when and were phenyl, but otherwise gave the isomers (85) and/or the adduct (84) by reacting with a further molecule of aldehyde. 

Yoshina and I. Maeba, Chem. and Pharm Bull. Japan), 1971, 19, 1465. 

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In this chapter, we consider two aspects of carbon-phosphorus bond formation as they relate to pentacoordinated phosphorus species. The first aspect is the preparation of stable phosphorane species — compounds bearing five bonds to phosphorus with at least one of them being a C-P linkage. At present, this is an area of rather specialized interest, but one that has potential for broader applications. 

The most interesting properties of phosphoranes, i.e. their role as intermediates or transition states of nucleophilic addition reactions of four-coordinate phosphorus compounds and their intramolecular rearrangements according to BPR or TR, have already been fully considered. The synthetic potential of stable phosphoranes has been reviewed by Burger in great detail (B-79MI11702), and only some special aspects need be mentioned in this chapter. 

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