Methylenetriphenylphosphoranes

The base catalyzed rearrangement of a monotosylated 1,2-diol on alumina, followed by immediate condensation of the sensitive ketone with methylenetriphenylphosphorane, gave the exo-methylene compound below (G. Btlchi, 1966B). 

A useful apphcation of phosphines for replacing a carbonyl function with a carbon—carbon double bond is the Wittig reaction (91). A tertiary phosphine, usually triphenylphosphine, treated with the appropriate alkyl halide which must include at least one a-hydrogen, yields the quaternary salt [1779A9-3] which is then dehydrohalogenated to form the Wittig reagent, methylenetriphenylphosphorane [19943-09-5] an yhde. 

The aldehyde group of laevulinic aldehyde reacted preferentially with the ester phosphorane (38), while the 2-acetyl groups of the benzofurans (39) were selectively methylenated with methylenetriphenylphosphorane. The aldehyde group was protected as the dimethylacetal in the synthesis of the steroidal a-methylene-aldehyde (40). 

The carbonyl group of the keto-acid (41) is remarkably unreactive towards methylenetriphenylphosphorane. Only 10% of unsaturated acid was obtained using a large excess of reagent in DMSO at 58 °C for several days. O... 

Optically pure quinic and shikimic acids have been synthesized starting from o-arabinose. The key steps involved treatment of the bis-tosylate (162) with 3 mol of methylenetriphenylphosphorane to give the ylide (163) which with formaldehyde gave the olefin (164) in 82% yield overall. 

The spectra of stabilized methylenetriphenylphosphoranes indicate that the Ph3P=C—C=0 and Ph3P=C—C=C—C=0 chromophores give maxima in the regions 275—305 and 350—400 nm, respectively. The... 

Methylenetriphenylphosphorane reacted with Zn N(SiMe3)2 2 in a multistep reaction (Scheme 78) to furnish initially the 1,3-dizincatacyclobutane 119, featuring two three-coordinate zinc atoms, and finally the cr-zincated phosphorus ylide 120.176... 

It however failed to react with methylenetriphenylphosphorane. Attempted partial hydrogenation of 65 using Lindlar s catalyst or 10% palladised charcoal led to none of the expected [13]annulenone e.g. 68. This may be due to the potential instability of the [13]annulenone which like its lower vinylogue cyclopentadienone 5 may undergo ready self-condensation. 

An alternative approach, in which the anomeric centre of the sugar is reacted with a carbon nucleophile, but the amino group is subsequently inserted at the other side or in both sides at the same time, is reported in Fig. 41 for the synthesis of a- and (3-homogalactonojirimycin.72 Reaction of 2,3,4,6-tetra-O-benzyl-p-D-galactopyranose with methylenetriphenylphosphorane generated an enitol on which the amino group was inserted as phtalimide by a double inversion process of the 5-OH, under Mitsunobu s conditions. 

Ketones. Treatment of the diketone (26) with methylenetriphenylphosphorane gave a high yield of 1,6-dimethylenecyclodecane.29 Diphenylcyclobutenedione reacts with ylides, e.g. (27), to yield substituted 4-methylene derivatives.30... 

Organometallics. Methylenetriphenylphosphoranes form stable 2 1 complexes (38)40 and 1 1 complexes (39)41 when treated with copper(i) or silver(i) chlorides. Stable adducts (40) can also be obtained from the reaction of methylenetrimethyl-phosphorane and metal trialkyls.42... 

A rather complex mixture of products is obtained from the reaction of benzyl-idenetriphenylphosphorane and CS2.48 The major product from the reaction of diphenyl disulphide with methylenetriphenylphosphorane is tris(phenylthio)-methane (44) and only a trace of the insertion product bis(phenylthio)methane is isolated.49 Presumably the salt (45) is deprotonated before it can react with the phenylthioate anion (Scheme 12). a-Thiocarbonyl-stabilized ylides (46) are obtained from the reaction of ylides with S-alkyl thiolcarboxylates.50... 

An acid- and base-sensitive siloxycarboxylic acid was treated with AW -carbonyldi-imidazole and the resulting imidazolide (51) transformed into the desired ylide using one equivalent of salt-free methylenetriphenylphosphorane in benzene, rather than two equivalents as usually recommended. Coupling, under neutral conditions, with two equivalents of aldehyde (52) gave a mixture of diastereomeric epoxythiolates (Scheme 15).68... 

Reaction of the ketones (93) with excess methylenetriphenylphosphorane gave, not only the expected methylene compounds, but also the diene (94) formed by elimina-... 

It is demonstrated that the formyl group in 35, prepared by silylformylation of 3-methyl-1-pentyne 34, reacts with methylenetriphenylphosphorane to give the corresponding 1,3-diene 307 (Equation (54)). This two-step transformation can be performed in one pot by carrying out the silylformylation in the presence of a stabilized Wittig reagent... 

The synthesis of phosphonium ylides by reaction of ( )-2-benzylideneoxazolidine-4,5-dione with methylenetriphenylphosphoranes has been reported12 these ylide phosphoranes have the structure PhCH2CONHCOCOCR=PPh3 with R = COOMe, COOEt and COPh. 

Pyrrolizid-l-one, obtained from the ethyl ester of L-proline (see Section II,E), was condensed with methylenetriphenylphosphorane to give 1-methylenepyrrolizidine, [a] 8 —33°, the IR spectrum of the latter compound was identical with that of the naturally occurring alkaloid. Notwithstanding the partial racemization of the base during... 

An intramolecular photocyclization catalyzed by copper(I) triflate provided a key step in a total synthesis of the ginseng sesquiterpenes a- and /J-panasinsene, (8) and (9). The unsaturated allylic alcohol (6) is cyclized by irradiation at 254 tun in the presence of CuOTf to a mixture of saturated alcohols, which is oxidized to the ketone 7. The ketone is inert to methylenetriphenylphosphorane, but can be converted into a 2 5 mixture of 8 and 9 by addition of mcthyllithium followed by dehydration.2... 

Another system, which is also allowed by IUPAC and is sometimes very convenient (but which should be avoided when official names are established by IUPAC and cited in Chemical Abstracts), is the so-called a -nomenclature, in which the term phospha indicates replacement of carbon by phosphorus, e.g. phosphacyclohexane = phosphorinane, and phosphabenzene = A3- phosphorin. Five-coordinate phosphorus compounds are called phos-phoranes. However, this name is also used for phosphorus ylides with a four-coordinate phosphorus and a more or less polar R3f—CX moiety or a d -p R3P=CX double bond, e.g. methylenetriphenylphosphorane = triphenylphosphorus methylene ylide or tri-phenylphosphonium methyl ylide, Ph3P=CH2 = Ph3P—CH2. 

A further illustration of the reaction of carbanionic species with o-hydroxybenzaldehydes is provided by the use of phosphorus ylides in coumarin synthesis. Thus, ethoxycarbonyl-methylenetriphenylphosphorane affords simple coumarins via the ester (380 R = H), whilst with o-hydroxyacetophenone a 4-methylcoumarin results (381 R = Me) (77S464), and 4-methylsulfinylmethylcoumarin (381 R = CH2SOMe) is obtained from o-hydroxy-a>-methylsulfinylacetophenone (Scheme 120) (72JHC175). 

---