Phosphoranes bonding

Phosphonium hexafluorophosphate, benzotriazolyl-N-hydroxytris(dimethylamino)-in peptide synthesis, 5, 728 Phosphonium salts chromene synthesis from, 3, 753 reactions, 1, 531 Phosphonium salts, vinyl-in pyrrole synthesis, 4, 343 Phosphonium ylides in heterocyclic synthesis, 5, 165 Phosphoramide, triethylene-as pharmaceutical, 1, 157 Phosphoramide, triethylenethio-as pharmaceutical, 1, 157 Phosphorane, pentaphenyl-synthesis, 1, 532 Phosphoranes, 1, 527-537 Berry pseudorotation, 1, 529 bonding, 1, 528... 

The solvated phosphorane adds to the polarized carbonyl with the incipient C-21 methyl group pointing away from the bulk of the steroid nucleus. The newly formed carbon-carbon bond must then rotate in order for the tri-phenylphosphine group and oxygen atom to have the proper orientation for the elimination of triphenylphosphine oxide. This places the C-21 methyl in the CIS configuration. 

A one-pot synthesis of alkyl perfluoroalkyl ketones has been developed. Phosphoranes, generated in situ, are acylated with a perfluoroacyl anhydnde, and the resultmg phosphonium salts are hydrolyzed with alkali [4S (equation 48) Hydrolysis of a carbon-sulfur bond in 2-chloro-2,4,4-trifluoro-1,3-dithietane-S-trioxide, which can be obtained from 2,2,4,4-tetrachloro-l,3-dithietane by fluor-mation with antimony trifluoride followed by selective oxidations, opens the nng to produce 2-chloro-1,1,2-trifluorodimethyl sulfone [49] (equation 49)... 

The teal value of the Wittig reaction is that it yields a pure alkene of defined structure. The C=C bond in the product is always exactly where the OO group was in the reactant, and no alkene isomers (except E,Z isomers) are formed. For example, Wittig reaction of cyclohexanone with methylenetriphenyl-phosphorane yields only the single alkene product methylenecyclohexane. By contrast, addition of methylmagnesium bromide to cyclohexanone, followed by dehydration with POCI3, yields a roughly 9 1 mixture of two alkenes. 

The phosphonium salt (116) gave the phosphorane (117) with phenyl-lithium although it has hydrogen atoms attached to carbon bonded to phosphorus. ... 

The cage-like phosphonium salt (17) with phenyl-lithium in THF gave the phosphorane (18) which probably owes its great stability to the relief of strain in the ring structure on changing the bond angle at phosphorus to 90°. For the photolysis of (18) see Chapter 10, Section 1. 

B. Electrophilic Reactions.—Transesterification followed by rearrangement is a common route from simple phosphites to more complex phos-phonates. This has now been applied to the preparation of cyclic phos-phonates (85). Both phosphites (86) and phosphoranes (87) containing phosphorus-hydrogen bonds are obtained from the cyclic biphosphite (88) and butanol. ... 

Structure, Bonding and Ligand Reorganisation. - An X-ray analysis of the monocyclic phosphorane (2) reveals a tbp structure with the hydrogen in an axial position and an H-P bond length of... 

The tetraoxahydrospirophosphorane (57) has been isolated in 66% yield from the reaction of (55) with triethylammonium perfluor-opinacolate (56). Hexafluoroacetone inserts into the P-H bond of (57) to form (58) which may also be obtained from (59) as shown1 1. The 1H and 19F n.m.r. spectra of the phosphoranes reveal rapid pseudorotational processes and a time-averaged conformation of a flattened chair for the six-membered rings. 

The first phosphorane (74) with a a"phosphorus-silicon bond has been prepared (albeit in low, 20%,yield) by the reaction of (72) with bis(trimethylsilyl)magnesium (73)99. It has an unusually high phosphorus chemical shift but no 2L ray data are, as yet, available. 

P oxygen transfer, presumably via (9). The structure of (10) was confirmed by X.-ray analysis and hydrolysis to give (11). An X-ray analysis of isopropylidenetri(isopropyl)phosphorane (12) suggests that the ylide P-C bond is relatively longer, and that the... 

Phosphorane 343 is interesting from another point of view as it represents a formal trapping product of the species 345 resulting from cleavage of one C—CO bond in cyclopropenone claimed earlier (p. 56). 

The reaction of 34 with triethylethylidenephosphorane is more complex. According to the multinuclear NMR data, the reaction occurs at the 1 2 ratio of the reactants. The Sn-O bond is cleaved to give phosphonium phenoxide (38) and stannylene (37) in which the tin atom is also bound to the ylide carbon atom of phosphorane (Scheme 17).61 Metallation reactions of this type are well known.61,75... 

Veith and Huch58 have made a tin dimer containing a deuterium atom on one of the groups bonded to the tin atom (Figure 2). This unusual tin compound was obtained when the acid-base adduct formed between 1,3-di-tert-butyl-2,2-dimethyl-1,3,2,4X2-diazasilastannetidine with triphenylmethylene-l,l-d2 phosphorane was heated at 120 °C in toluene (equation 54). 

Carbon-phosphorus bond formation involving phosphorane intermediates... 

The present effort is intended to provide an update of the earlier edition, bringing to the chemist in concise form advances in the approaches to C-P bond formation previously discussed, as well as several other aspects of C-P bond formation. These latter aspects include the generation of organophosphorus compounds from elemental phosphorus (of particular industrial interest for purposes of cost containment) advances in the preparation of phosphoranes, including the use of transient oxophosphoranes as intermediates in organophosphorus compound syntheses and new approaches toward the preparation of compounds with aromatic and vinylic carbon-phosphorus bonds. 

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 fact that tetrazolo[l,5- ]pyridine reacts with phosphines - via ring opening to the valence bond isomer azide -to give a phosphorane has been long recognized. Some novel applications of this transformation have been published during the recent period. The fused tetrazoles subjected to this reaction, the resulting phosphoranes, and the literature sources are summarized in Table 4. 

Preparative details and extensive i.r., n.m.r., and mass spectra have been described for the phosphoranes (87).48 These phosphoranes have a TBP structure, and for (87a)—(87c) their n.m.r. spectra are temperature-independent, and indicate that the fluorines bonded to phosphorus are equivalent. The authors have suggested an explanation based on rapid intramolecular isomerization, and discussed the possibility that a facile TR pathway exists for this process.46 Octahedral adduct formation between (87) and fluoride ion or trimethylphosphine has also been described,46 as shown in (88). 

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... 

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