Ketophosphonates rearrangement

The vinyl phosphate-P-ketophosphonate rearrangement has also been explored with substituted cyclohexenones. The treatment of enones with LDA under conditions of kinetic control and subsequent reaction with diethyl chlorophosphate gives a single dienyl phosphate. On treatment with an additional equivalent of LDA, a single phosphonate is formed, the regioisomer with a C-P bond at the a -position of the resulting a,P-unsaturated ketone. The respective phosphonates are isolated in an average yield of 70% (Scheme 7.38). ... 

The vinyl phosphate-P-ketophosphonate rearrangement can be used to prepare a-phosphono-lactones in high yields (68-78%, Scheme 7.39). 5o gy variable-temperature P-NMR study it has been shown that abstraction of a proton from the vinyl phosphate is the slow step in the rearrangement and that, once this anion is formed, tlie rearrangement to the phosphonolactone is facile. 

To explore the viability of chiral auxiliaries in the vinyl phosphate-p-ketophosphonate rearrangement, a series of vinyl phosphates derived from ephedrine, pseudoephedrine, (lR,2S,5R)-(-)-menthol, (15,25,35,57 )-(-i-)-isopinocampheol, (5)-(-)-2-methylbutanol, binaphtol, and (2R,4R)- or (25,45)-pentane-2,4-diol have been examined. (5)-(-)-2-methylbutanol and 2,4-pentane-2,4-diol derivatives appear as the most attractive chiral auxiliaries. 

The Beckmann rearrangement of oxime mesylates initiated by TiCU has been applied to the preparation of 1,2-dehydro-1-aminoalkylphosphonates, e.g. 201, through trapping of the intermediate with triethyl phosphite. Oximes of a-ketophosphonates are often difficult to reduce to the corresponding 1-aminoalk-... 

The thermal rearrangement of diarylcyclobutenones 353 gives the naphthol derivatives 354 (equation 169) . The cyclobutane derivatives 355 undergo a retro-Diels-Alder reaction and rearrangement to produce naphthol 356 (equation 170) . The formation of cyclobutene intermediate 358 was assumed for the transformation of trans-a-diazo-fi-ketophosphonates 357 into naphthols 359 (equation 171). ... 

Several routes to P-ketophosphonates that rely on electrophilic phosphorus reagents have been developed. One of the most important involves the rearrangement of vinyl phosphates to P-kclophosphonales. Thus, when camphor is treated sequentially with LDA and diethyl chlorophosphate at low temperature, the vinyl phosphate is produced quantitatively. When this product... 

The reaction of the sodium salt of. V-phenylhydroxylamine with diethyl allenylphosphonate in THE in the presence of (TjCOgLi gives, by Michael addition and Cope rearrangement, y-(ortho-aminoaryl)-P-ketophosphonates, which are easily converted into diethyl 2-indolylmethylphospho-nates in high yields (Scheme 7.118). 28 29... 

Gallant, P, D Haenens, L., van derEyken, E., and Vandewalle, M., Photoinduced Wolff rearrangement of a-diazo-P-ketophosphonates. A novel entry into substituted phosphonoacetates, Synth. Commun., 14, 163, 1984. 

Diethyl enol phosphate 47 rearranges to p-ketophosphonates 49 upon treatment with LDA.34 This reaction probably proceeds via cleavage with LDA to give an enolate phosphonium ion pair 48 which then interacts to give the anion under equilibrium conditions.34 The reaction mixture is quenched with acetic acid. The enol phosphate 47 is prepared by Perkow reactions from the corresponding a-halocyclohexanone.34... 

Dialkyl end phosphate of lactone 58 undergoes rearrangement to p-ketophosphonate 59 upon treatment with LDA at-100 °C. The enol phosphate of lactone 57 is made by (1) treatment of lactones with LDA to give the lithium enolate, (2) O-phosphorylation of the enolate with dialkyl chlorophosphoridate in THF-HMPA under kinetic conditions, or (3) a one step conversion without isolation of the intermediate enol... 

The synthesis of (-h )-polyoxamic acid (435), the unusual amino acid component of polyoxin B, incorporates backbone assembly via a Homer- Emmons olefination of L-tartrate-derived aldehyde 430 with (i )-lactate-derived jS-ketophosphonate 914 [101] (Scheme 122). The key introduction of the chiral amine stereocenter is accomplished by a trifluoroacetimidate rearrangement, outlined in Scheme 60 (Section 1.4.7.2). 

The reaction of several a-diazoketones with ethyl vinyl ether under various conditions has been examined. In the presence of metal salts [Rh2(OAc)4, Pd(OAc)2, CuCl] ethoxy dihydrofurans are produced. The initial product of this reaction sequence is a cyclopropyl ketone which suffers from a spontaneous rearrangement to the dihydrofuran <96CJC2401>. An efficient synthesis of 3-acylfurans is achieved by Ag(I)/Celite mediated cycloaddition of dicarbonyl compounds with vinyl sulfide (<97TL5671> see also <97TL2095>). A two-step synthesis of 2-substituted 4-furanmethanol compounds was reported. The method involves a Homer-Wadsworth-Emmons reaction between 3-ketophosphonates and l,3-diacetoxy-2-... 

RJi (II) catalyzed conversion of 2-diazo-jd-ketophosphonates 166 via a Wolff rearrangement in toluene under reflux was suggested to give ketenes 167, which simultaneously via the intramolecular nucleophilic attack of the ether-oxygen followed by migration of the silyl group to afibrd the ketene... 

The benzoylphosphonate (168) underwent cyclisation and deoxygenation in the presence of excess trimethyl phosphite to give the corresponding benzofuran (170). ° The reaction pathway involved the phosphite attack on the initially formed, tricyclic dioxaphospholane intermediate (169) with the subsequent loss of two molecules of trimethyl phosphite. In the absence of the additional molecule of P(OMe)3, the initially formed (169) underwent a loss of trimethyl phosphite and a subsequent rearrangement to the p-ketophosphonate (171) (Scheme 59). 

The jS-ketophosphonate 1,4-dianion (16), obtained by tin-lithium exchange at -78 C is a direct homoenolate, electrophiles adding exclusively at the terminal site. On warming to 0 C, the dianion rearranges to the 1,3-isomer, becoming the bis-enolate. In view of the known transformations of /8-ketophosphonates, the stannane (17) becomes a precursor for both a - and jS -substituted a,jS-unsaturated ketones (Scheme 13). 

A catalytic enantioselective Claisen rearrangement of enolphosphonates to a-ketophosphonate derivatives (Scheme 6) ° and a chelate Claisen rearrangement for the stereoselective synthesis of / -substituted y,5-unsaturated ammo acids" have been reported (Scheme 7). 

Yamamoto et al. have successfully developed the first copper-catalysed enantioselective Claisen rearrangement of enolphosphonates (353). A number of desired a-ketophosphonates (354) have been obtained in excellent yields and stereoselectivities (Scheme 120). ... 

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