Allyl phosphates

Many examples of stereospecific allylation consistent with the above mechanism have been reported. As one example, the regioselective and highly diastereoselective allylation of the lactone 17 with the optically active allylic phosphate 16 proceeded with no appreciable racemization of the allylic part to give the lactones l8 and 19, and the reaction has been used for the synthesis of a polypropionate chain[26]. 

Allylation under basic conditions. Allylation can be carried out under basic conditions with allylic acetates and phosphates, and under neutral conditions with carbonates and vinyloxiranes. The allylations under neutral conditions are treated separately in Section 2.2.2.1 from those under basic conditions. However, in some cases, allylations of the same substrates are carried out under both basic and neutral conditions to give similar results. These reactions are treated together in this section for convenience. Allylic acetates are widely used for Pd-catalyzed allylation in the presence of bases tertiary amines or NaH are commonly used[6,7,4l]. As a base, basic alumina or ICF on alumina is conveniently used, because it is easy to remove by filtration after the reaction[42]. Allyl phosphates are more reactive than acetates. The allylation with 40 proceeds stepwise. At first allylic phosphate reacts with malonate and then allylic acetate reacts with amine to give 41(43]. 

Allylic phosphates are used for carbonylation in the presence of amines under pressure. Carbonylation of diethyl neryl phosphate (389) affords ethyl homonerate (390), maintaining the geometric integrity of the double bond[244]. The carbonylation of allyl phosphate in the presence of the imine 392 affords the /3-lactam 393. The reaction may be explained by the formation of the ketene 391 from the acyl phosphate, and its stereoselective (2 + 2] cycloaddition to the imine 392 to give the /3-lactam 393(247],... 

Scheme 30 represents the energy diagram for the photorearrangement shown in Scheme 29. Quenching of the triplet state of the sensitizer by the cis allyl phosphate, c/s-1, generates the triplet state, T , of the 1,2-biradical 2. The 1,2-biradical is trapped by the phosphorus atom to afford the triplet state, TP, of the spirophosphoranyl 1,3-biradical 3. Then, inter-system crossing generates the...

The Ag complex 121 in the presence of CuCl H O or CuCOTO CgHg catalyses the allylic alkylations of allyl phosphates by diaUcylzinc reagents with high enantiose-lectivity (Scheme 2.23). A copper complex 122 which is the precursor to the catalytic species was also isolated and structurally characterised (Figs. 2.21 and 2.22) [99]. 

Scheme 1.66 Cu-catalysed allylic alkylations of allylic phosphates with vinylalumi-num reagents in the presence of sulfur-containing diaminocarbene ligands.

Hoveyda and co-workers also tested optically active A-heterocyclic carbenes and their silver complexes in copper-catalyzed reactions of allylic phosphates with dialkylzincs.402 The ratios of Sn2 SN2 products were higher than 98 2 and the ee varied from 34% to 98%. 

Surprisingly, only a single application of a copper(I)-catalyzed cross-coupling of metallated allenyl species has been reported [44]. The CuBr-catalyzed coupling of allenylmagnesium bromide (82) with allyl phosphate 83 provided 6-butyldeca-l,2,5-triene (84) in high yield, as depicted in Eq. 14.8. 

The simple procedure for the carbonylation of allyl halides has been extended in the high yielding solid-liquid two-phase conversion of allyl phosphates into amides (60-80%) under the influence of a rhodium carbonyl cluster in the presence of primary or secondary amines (Scheme 8.8). A secondary product of the reaction is the allylamine, the concentration of which increases as the pressure of the carbon monoxide is reduced, such that it is the sole product (ca. 80%) in the absence of carbon monoxide [28],... 

Conversion of allyl phosphates into p,runsaturated amides (Table 8.10)... 

Scheme 2.S6. Copper(l)-catalyzed anti-S l substitution of allylic phosphates.

The O-substitution products of oximes can be readily cleaved to give the corresponding alcohols. The (Ph-Pybox) Ir catalyst worked well at low temperatures with allyl phosphates as substrates (Scheme 9.36) [40, 63]. The selectivities depended heavily on the base used for activation of the oxime with, again, the best results being obtained with Ba(0H)2-H20. Only arylallyl phosphates have been reported as substrates. 

Scheme 16 Synthesis of the allylic silane 89 by an 5 2 displacement of an allylic phosphate...

The introduction of the allylic silane moiety required for the intermolec-ular Hosomi-Sakurai reaction is depicted in Scheme 16. Following the formation of the enol triflate 97, a Stille coupling provided excess to the allylic alcohol 98 [51]. The allylic alcohol (98) was endowed with a phosphate leaving group for the subsequent allylic substitution. Utilizing a trimethylsilyl cuprate as nucleophile for the 5 2 reaction, the allylic phosphate was converted into the allylic silane 89. A useful substrate-induced diastereoselectivity in favour of (14i )-89 was encountered at small scale but decreased significantly upon up-scaling. 

The synthesis of Abu[PO(OH)2]-peptides is also accomplished via the use of Fmoc-Abu-[PO(OAl)2]-OH (22) with the allyl phosphate ester being cleaved by Pd(0)-mediated treatment. Fmoc-Abu[PO(OAl)2]-OH (22)t101] is prepared from Schollkopfs (-)-bislactim ethyl ether 21f102] by a four-step procedure that involves initial treatment of the lithium salt of... 

Takemoto and his co-workers developed asymmetric allylic alkylation of allylic phosphates with (diphenyl-iminolglycinates as carbon-centered nucleophiles (Equation (56))/" " In this reaction system, use of optically active bidentate phosphites 142 bearing an (ethylthio)ethyl group as chiral ligands promotes the allylic alkylation, and chiral /3-substituted a-amino acids are obtained with an excellent enantioslectivity. 

Propargylic mesylates such as fluorine-substituted derivative 265 react with PhZnCl in the presence of Pd(PPh3)4 (5 mol%) in THF at 0°C within 2 h to provide the anti-Si 2 product in excellent yield and complete transfer of the stereochemistry leading to the allene 266 (Scheme 78). Copper(I) catalyzed allylic substitutions with functionalized diorganozincs proceed with high 8 2 selectivity. Thus, the reaction of the chiral allylic phosphate 267 with 3-carbethoxypropylzinc iodide in the presence of CuCN 2LiCl (2 equivalents) furnishes the awf/-Sjv2 substitution product 268 in 68% yield. By the addition of w-BuLi (1.2 equivalents) and TMSCl (1.5 equivalents), the bicyclic enone 269 is obtained in 75% yield and 93% ee (Scheme 79) . 

As reported (J. Org. Chem. 68 6197,2003) by Yoshjii Takemoto of Kyoto University, a-amino acids can be prepared in high enantiomeric and diastereomeric excess by Ir-mediated two-carbon homologation of allylic phosphates such as 9 with the protected glycine 10. Either diastereomer can be made dominant by varying the reaction conditions. 

BuySnAl(CjHs)2 (12, 339-341). Reaction of allylic phosphates with this reagent (1) and a Pd(0) catalyst affords allyltin compounds, which react with aldehydes to produce homoallylic alcohols in 65-85% yield. The reaction involves predominant inversion of stereochemistry.1... 

These results were obtained by performing the reactions in slightly different conditions than those used by Torii and coworkers. For instance, they reported the palladium-catalyzed cyclocarbonylation of allyl phosphate with imines in a stereoselective manner, depending on the imine used for the coupling, (Scheme 66), but they could not obtain any reaction product starting from allyl halides [161]. 

Scheme 66 Palladium-catalyzed cyclocarbonylation of allyl phosphate with imines...

The palladium-catalyzed carbonylation reaction of allyl diethyl phosphate, in the presence of imines, gives either cis- or rraws-3-vinyl-/J-lactams, in high yields and in a stereoselective fashion (equation 160)574,575. The reaction is a [2 + 2] cycloaddition process which occurs under simple and mild conditions and has significantly more potential than the reaction of imines with ketenes (due to the more forcing conditions that are usually required to form the ketene intermediates). This reaction, however, only proceeds in low yield if the allyl phosphate is replaced with allyl acetate576. 

Allyl phosphates, 506 Allylsilanes, 43, 71-72, 529, 575 Allyl sulfones, 512 Allyltitaniiun ate complexes, 376-377 Allyltri-n-butyltin, 15-16 Allyltrimethylsilane, 16-20, 532 Allyltrimethyltin, 20-21 Almusone, 51 Alpine Boranc, 429 Alumina, 22-24 Aluminum amalgam, 24-25 Aluminum ate complexes, 17 Aluminum chloride, 25-28, 100 Aluminum chloride-ethanethiol, 28-29 Aluminum isopropoxide, 29, 296 Amidoalkylation, 16-17 Amidomercuration, 317 Animation, 221 Amino acid esters, 360... 

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