With methylenephosphoranes

As shown for the aziridines, BETMIP (68) has proved to be useful in the synthesis of azepines (Scheme 118). Treatment with methylenephosphorane leads to a phosphonium salt which in turn is deprotonated with BuLi and cyclized with benzene-l,2-dialdehyde in a Wittig and aza-Wittig step to form benzazepine 326 (93JOC1987). 

A convenient, short-step synthesis of enantiomerically pure 2-methylenecyclopropyl-methanol has been achieved by treating optically pure epichlorohydrin with methylenephosphorane (equation 146)325. Vinyl ketones are cyclopropanated with ( )-1-... 

Reactions of Ketones with Methylenephosphoranes.—Intramolecular Wittig reactions have been used to prepare a variety of cyclic compounds including bicyclic alkenes (41) and cyclic imines. In a similar way both Wittig and phosphonate reactions can be used to synthesize many strained bicyclic alkenes (42), but fail with the most strained examples, e.g., (43). Intramolecular Wittig... 

This reaction may be visualized as proceeding by nucleophilic attack of tervalent phosphorus at the carbonyl group to give an intermediate such as (15). The structure of (16) was deduced from the fact that it was hydrolysed to the known phosphine oxide (17). Methylenephosphoranes (phosphorus ylides) may also be converted into monophosphazenes by reaction with benzonitrile ... 

The first silicon-organophosphorus betaine with a thiolate center (15a) was synthesized by the reaction of stable silanethione (14) with trimethyl-methylenephosphorane (Scheme 8) and characterized by multinuclear NMR spectroscopy.14 Compound 15a is formed under kinetic control and is transformed, under the thermodynamically controlled conditions, into the silaacenaphthene salt (16). The processes presented in this scheme reflect the competition of the basicity and nucleophilicity of phosphorus ylides. Betaine 15b prepared from less nucleophilic and less basic ylide with phenyl substituents at the phosphorus atom is much less resistant toward retro-decomposition compared to the alkyl analog. Its equilibrium concentration does not exceed 6%. 

Structure.—N.m.r. evidence has been presented which shows that the compounds generated by the reaction of butyl-lithium with methylphosphonium salts are not methylenephosphoranes, but lithium adducts of the ylides,14 and that they are planar18 (see Chapter 12). A carbonyl group separated by a benzene ring as in (12) has a weak stabilizing effect.16... 

Methylenation using diazomethane, 2 78 Methylene, 29 303-304 Methylene blue, astatination, 31 77 Methylenephosphoranes, reaction with hexafluoroacetone, 30 258... 

The Wittig reaction of 6-methoxy-4-methylbenzofuran-2-carbaldehyde with methoxy-methylenephosphorane gave a 2 1 mixture of (E)- and (Z)-6-methoxy-2-(/3-methoxyvinyl)-4-methylbenzofuran, which was used directly in a Diels-Alder reaction with dimethyl acetylenedicarboxylate, a key step in the route to polyfunctional dibenzofurans (70AJC2119). The di-O-methyl derivative (397) of the lichen natural product strepsilin was synthesized by this route (Scheme 106) (72AJC545). 

Leukotriene-B could be obtained starting with the aeetonide 88 of 2-deoxyribose 76). Wittig olefination of 88 with methoxycarbonyl-methylenephosphorane 67 and subsequent hydrogenation affords hydroxy ester 89. Tosylation of 89, cleavage of the protective group and treatment with K2C03 yields the epoxy ester 90. Benzoylation... 

Wittig reactions have been found in several cases when HFA reacts with substituted methylenephosphoranes 209,213,245,249), by analogy with the... 

Methylquinazolin-4(3//)-one is obtained m 75 % yield via an unusual methylenephosphorane extrusion process on heating salt 36 in acetonitrile under reflux with a catalytic amount of sodium hydrided ... 

Coupling of aromatic diazonium salts with stabilized methylenephosphoranes leads to arylazometh-ylenephosphoranes (equation 30). ... 

Reaction of simple ylides with dialkyldihalosilanes leads in a twofold transylidation to the formation of Si-bridged bisphosphoranes (equation 42), which can undergo consecutive reactions with excess starting materials leading to cyclic products. Bis(chlorodimethylsilyl)methane also reacts with dilithio-methylenetrimethylphosphorane to give a methylenephosphorane with an exocyclic ylide function (equation 43). 

Ylides with ambident character, like 1-formyl- or 1-acyl-methylenephosphoranes, may be attacked by alkylating reagents (the same is true for acylation) at the a-carbon or at the O atom. - Bromomethyl acetate C-alkylates acylmethylenetriphenylphosphoranes in a transylidation reaction (equation 55). Recently cyanomethylenetriphenylphosphorane has been successfully alkylated via its ylide anion, the substituted cyano ylides being accessible more readily in greater variety than previously (equation 56). ... 

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. 

Pretreatment of the monomethylenediphosphazene with sodium or n-butyl-lithium, followed by methyl iodide, resulted in the formation of a methylenephosphorane, (MePhN-PPh2=CH-PPhaMePh)+1. The same compound could also be converted into an imide by reaction with an aldehyde ... 

Miscellaneous Reactions of Methylenephosphoranes.—The synthesis of three-membered rings by means of phosphorus ylides has been reviewed and there have been several new reports of this type of reaction. Optically active a,p-un-saturated esters have been converted into cyclopropanes highly stereoselectively by reaction with isopropylidenetriphenylphosphorane as the key step in syntheses of both (li ,3 )-chrysanthemic acid methyl ester (53) and the (IR) cis-gem dibromovinyl analogue (54). The addition of reactive phosphonium ylides to functionalized 1,3-butadienylphosphonates provides a new synthesis of 2-cyclopen ten-1 -ylphosphonates (5 5). ... 

However, the information on fluorine-containing derivatives of these materials is very limited. P-F Phosphoranes 193 and 194, resulted from the fluorination of diphosphine disulfide 192 or from the reaction of 1-methyl-methylenephosphorane 191 with hydrogen fluoride, were among the first representatives of the fluorine-containing phospholanes. ... 

In another synthesis methylenephosphorane (137) was reacted with a-methoxyisobutyric acid chloride (138) to give the phosphorane 139 which was elongated to the alcohol 140 in a Wittig reaction with the aldehyde 141. Treatment with triphenylphosphine hydrobromide gave the Cis-phosphonium salt 142 and a Wittig reaction with the Cio-dialdehyde 20 provided 2,2 -diketospirilloxanthin (416) [16,17] (Scheme 32). 

Trimethylsilylmethylenephosphoranes have two different electrophilic sites (P, Si). Reaction of these species with methanol generates methoxytrimethyl-silane and methylenephosphoranes (51). Apparently silicon is a harder acceptor than tetrahedral phosphorus. 

At least three names are available for the compound H3P=CH2. These are phosphine methylene, methylene phosphonium ylid and phosphonium methylide moreover, the compound can be classed as a phosphorane The compound PhjP Rj may be called triphenylphosphonium methylide, tri-phenylphosphonium methanide or triphenyl-methylenephosphorane. The pyridine analogue, C5H5P, has been known variously as phosphobenzene, phosphabenzene, phosphorin, and most recently, phosphinine. The term phosphane for (1) in Table 1.4 and its derivatives is the most recent and the most systematic, but it is difficult to see how the more widespread and firmly rooted term phosphine will ever be replaced. In addition, adoption of the term phosphane would put it in line with such little-used terms as carborane for CH4, nitrane for NH3 and oxane for HjO. 

A new ylide, tris(4-methylphenyl-)benzoylmethylenephosphorane, has been synthesized and its properties and reactivity studied.The metallation of the donor-functionalized ylide ligand (2-methoxyphenyl)methylene-triphenylphosphor-ane with conujlexes of yttrium and lutetium gave unprecedented phosphoranylidene complexes.The reaction of triphenyl-methylenephosphorane with Mo(NAr)-(CHCMe3)[OCMe(CF3)2l2> (Ar = 2,6- Pr2QH3), produced an anionic alkylidyne complex (Scheme 103). ... 

A few examples of the reactions of a (trimethylsilyl)methylenephosphorane with carbonyl compounds have been reported. Reactions of the silylated phosphorus ylide 106 with a,/ -unsaturated aldehydes lead to the 1,3-dienylphosphonium salts 107 (Scheme 2.64) [170). These reactions show that the silyl group is eliminated faster than the phosphorus group. 

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