Allylic phosphate esters

High y-selectivity has been observed for allylic diphenyl phosphate esters.26a O... 

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... 

Allylic halides are not as readily accessible as allylic alcohols or their ester derivatives. Thus, the requirement that allylic halides must be used as precursors for carbonyl addition reactions in conjunction with magnesium and other similar reductants is a severe restriction limiting the convenience of these routes to homoallylic alcohols. In this regard, samarium diiodide can be used to great advantage, because substrates other than allylic halides are suitable precursors for such transformations. For example, allylic phosphate esters have been reported to couple with carbonyl substrates in the presence of Smh (equation 15). Since esters and nitriles are unreactive under these conditions, the Smh-mediated process is likely to be more chemoselective than those promoted by magnesium or lithium. 

Allylation of all these species is apparently less selective (Scheme 69, entry a), and among the various thioacetals tested 1,3-dithianes proved to be the ones which lead to the highest 0 7 The use of HMPA as a cosolvent was shown to have no effect on the regioselectivity of the allylation. However, both exclusive 7-allylation and 7-methylation have been achieved by performing the reaction in the presence of copper(I) iodide-trimethyl phosphite complex (Scheme 69, entries a-e). The reaction is best achieved with allylic chlorides, bromides and phosphate esters and does not occur with acetates, although these compounds usually react with cuprates. In all cases where isomers could be formed with respect to the electrophile, the ratio of 5n2 5n2 products was found to be greater than 0.67 (Scheme 69, entries b-e).- Related reactions have already been described with allylic sulfides (Scheme 27, see Section 1.3.2.2.4). 62.iM... 

Dienes. The coupling of allylbarium reagents with allylic bis-12.2,2-trifluoroethyl)phosphates proceeds at a and a positions and is thus different from that of Grignard reagents (a,y cross coupling). Hence, little transposition occurs with the use of the allylic phosphate esters in these reactions. 

Kitagawa Y, Hashimoto S, lemura S, Yamamoto H, Nozaki H (1976) Novel nonenzymic heterolysis of an allyl phosphate ester by organoaluminum reagents. J Am Chem Soc 98 5030... 

Pd(Ph3P)2Cl2(Bu3SnH, benzene) or cobalt carbonyl. The palladium method cleaves allyl esters, propargyl phosphates, and propargyl carbamates as well. 

Although most of these early reactions were conducted with allylic acetates, reactions of allylic carbonates, trifluoroacetates, and phosphates also occur. Sodium diethylmalonate also reacts with allylic alcohols in the presence of the iridium-triphenylphosphite catalyst. However, the alcohol itself does not act as a leaving group. Instead, transesterification occurs with one equivalent of malonate nucleophile to form a more labile ester leaving group. 

Addition to linear 1,1-disubstituted allylic acetates is slower than addition to monosubstituted allylic esters. Additions to allylic trifluoroacetates or phosphates are faster than additions to allylic carbonates or acetates, and reactions of branched allylic esters are faster than additions to linear allylic esters. Aryl-, vinyl, alkynyl, and alkyl-substituted allylic esters readily undergo allylic substitution. Amines and stabilized enolates both react with these electrophiles in the presence of the catalyst generated from an iridium precursor and triphenylphosphite. 

Previous methods for the preparation of salts of geranyl diphosphate and other allylic isoprenoid diphosphates are based on condensation between the alcohol and inorganic phosphate by trichloroacetonitrile as originally reported by Cramer and modified by Popjak The reaction generates a complex mixture of organic and inorganic polyphosphates which must be separated by chromatography. The desired diphosphate ester has been prepared on small... 

A combination of rhodium complexes and phosphates promotes a highly regioselective allylic alkylation of unsym-metric allylic esters, where alkylation occurs at the more substituted allylic terminus of the esters (Equation (46)). As Evans and his co-workers reported, both the regio- and stereochemistry of the starting allylic esters are maintained in the allylic alkylated products (Equation (47)). Thus, the rhodium-catalyzed allylic alkylation takes place at the carbon substituted by a leaving group with net retention of configuration. A variety of carbon-centered... 

As described in many reviews, Trost and his co-workers have carried out a pioneering work on the molybdenum-and tungsten-catalyzed allylic alkylation of allylic esters regioselectivity of the reaction is often complementary to the palladium-catalyzed allylic alkylation. The first asymmetric version was disclosed by Pfaltz and Lloyd-Jones in 1995 (Equation (63)). They used a catalytic amount of a novel tungsten complex, prepared from [W(CO)3(MeCN)3] or [W(cycloheptatriene) (COIs] and optically active (diphenylphosphino)phenyloxazolines 57, for the allylic alkylation of 3-aryl-2-propenyl phosphate with dimethyl sodiomalonate to isolate the corresponding branched alkylated compounds as a major isomer with an excellent enantioselectivity (96% ee). Unexpectedly, 3-aryl-2-propenyl carbonates are shown to be unreactive. It is worth noting that an isostructural molybdenum complex does not promote the catalytic alkylation under the same reaction conditions. In contrast, Lloyd-Jones and Lehmann reported the stereocontrolled... 

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