Phosphoranes synthesis

Extension of the Phosphorane Route. Ample evidence of the versatihty of the phosphorane synthesis strategy is provided by the proliferation of penems that followed. Nucleophilic displacement of the acetate function of the acetoxy-azetidinone (51, R = OCOCH ) [28562-53-0] (86) provided azetidinones where R = SCOCH, SCSSC2H, and SCSOC2H, which on elaboration gave the penems (52, R = CH ) (87), (52, R = SC2H ) (88), (52, R = 0C2H ) (89). Similar treatment of 3-substituted (or disubstituted) acetoxyazetidinones allowed the synthesis of a number of 2-substituted- 6-alkyl-and 6,6-dialkylpenems (90). 

Metallobis(methylene)phosphorane, synthesis with phosphaalkenes, 19-20... 

Returning to the simplest variation of the three component phosphorane synthesis, about 20 new heterocyclic products were described using indoles,2-indoli-none, S-acetylindole, " carbazole ° and its derivatives, pyrazole and imidazol derivatives, their benzoanellated analogues and benzotriazoles " as the A -nucleophiles (Scheme 113). 

Surprisingly carbonyl-substituted carbanions of phosphonates, in which the negative charge is delocalized over two oxygen atoms, are much more nucleophilic than the corresponding phosphoranes. This effea has first been observed by Homer, and has often been utilized in the synthesis of acylated olefins (R.D. Clark, 1975). 

Synthesis. The first hiUy alkyl/aryl-substituted polymers were reported in 1980 via a condensation—polymeri2ation route. The method involves, first, the synthesis of organophosphine-containing alkyl or aryl substituents, followed by the ready oxidation of the phosphine to a phosphorane with leaving groups suitable for a 1,2-elimination reaction. This phosphorane is then thermally condensed to polymers in which all phosphoms atoms bear alkyl or aryl substituents. This condensation synthesis is depicted in Eigure 2 (5—7,64). 

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... 

Olefin synthesis Irom phosphorane ylides (e g 3) with aldehydes or ketones cis olelins predominate in aliphatic systems trans m coniugated olefins... 

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 formation of 27a-27e, 28, and 29 makes use of a chemistry developed by Akiba and coworkers in the 1990s for the synthesis and applications of cyclic lO-P-5 phosphoranes made of two Martin ligands. Methyl, benzyl and phenylth-... 

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). 

A mechanism for this reaction involving nucleophilic attack of the ylide on the cyanide group and formation of the P=N linkage via a four-centred intermediate was formulated. The structure of this phosphazene was confirmed by its synthesis from the vinyl azide, Ph(N3)C=CHPh, and triphenylphosphine. Phosphoranes stabilized by electron-withdrawing... 

The pentacoordinate intermediate is the analog of the tetrahedral intermediate, and stable phosphoranes are the analogs of ortho esters and related species in carbon chemistry. Ph3P(OPh)2 and P(OPh)5 were reported in 1959, and in 1958 a general synthesis of pentaalkoxy phosphoranes containing an unsaturated five-membered ring was reported. In 1964 a synthesis of pentaethoxyphosphorane was devised which led to the preparation of a number of saturated and unsaturated pentaalkoxy... 

If the acyl moiety is sensitive to acid and base the imidazolide method for synthesis of (acylmethylidene)phosphoranes is the method of choice, as shown by the following example, which represents a step on the way to the antibiotic methynolide ... 

This is an extremely useful reaction for the synthesis of alkenes. It involves the addition of a phosphonium ylid, e.g. (136), also known as a phosphorane, to the carbonyl group of an aldehyde or ketone the ylid is indeed a carbanion having an adjacent hetero atom. Such species are generated by the reaction of an alkyl halide, RR CHX (137), on a trialkyl- or triaryl-phosphine (138)—very often Ph3P—to yield a phosphonium salt (139), followed by abstraction of a proton from it by a very strong base, e.g. PhLi ... 

A solvent-free synthesis of benzo[b]furan derivatives 10-79, a class of compounds which is often found in physiologically active natural products, was described by Shanthan Rao and coworkers. These authors heated phosphorane 10-71 for 8 min in a microwave oven and obtained the benzo[b]furan 10-74 in 73% yield (Scheme 10.18) [25]. The sequence is initiated by an intramolecular Wittig reaction, providing alkyne 10-72 this underwent a subsequent Claisen rearrangement to give the intermediate 10-73. Also in this case, normal oil-bath heating gave much lower yields (5%) of the desired product the authors hypothesize that the micro-... 

Kelly, J.W., Robinson, RL., and Evans, S.A., The synthetic utility of dioxy-phosphoranes in organic synthesis, Phosph. Sulf, 26, 15, 1986. 

Table 4 Synthesis of some phosphoranes from tetrazolo[1,5-a]pyridines and its benzologues...

Ding et al. published a synthetic route to the related fully conjugated linearly fused triazoloquinazole 493 <2004EJO3872>. The synthesis started from the phosphorane 492 treatment of this compound with arylisocyanates (via the formation of a carbodiimide side-chain intermediate) gives rise to product 493 in excellent yield. 

Polyene synthesis. The Vedejs trienic phosphorane 1 (6,14-15) is useful for synthesis of bifunctional all-tram polyenes, since the mixture of (E)- and (Z)-... 

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