Allyl carbonates optically active

Allylsilanes are available by treatment of allyl acetates and allyl carbonates with silyl cuprates17-18, with antarafacial stereochemistry being observed for displacement of tertiary allyl acetates19. This reaction provides a useful asymmetric synthesis of allylsilanes using esters and carbamates derived from optically active secondary alcohols antarafacial stereochemistry is observed for the esters, and suprafacial stereochemistry for the carbamates20,21. 

An efficient chemoenzymatic route for the synthesis of optically active substituted indolines has been recently developed (Scheme 7.27), and also the alkoxycarbonyla-tion process is more efficient than the acylation reaction. Different lipases have been tested in the alkoxycarbonylation of these secondary amines, GALA being found to be the best biocatalyst for 2-substituted-indolines, and CALB for 3-methylindoline. The combination of lipases with a variety of allyl carbonates and TBME as solvent has allowed the isolation of the carbamate and amine derivatives in a high level of enantiopurity [51]. 

Allyl p-tolyl sulphoxide 535 reacts with sodium methoxide in methanol by initial prototropic isomerization and subsequent addition of methanol to give 536 (equation 333). Protic solvents are photochemically incorporated by the open chain olefinic bond of trans methyl )S-styryl sulphoxide 537 in a Markovnikov regiospecificity (equation 334). Mercaptanes and thiophenols add to vinyl sulphoxides in a similar manner (compare also Reference 604 and Section IV.B.3) to give fi-alkylthio(arylthio)ethyl sulphoxides 538 (equation 335). Addition of deuteriated thio-phenol (PhSD) to optically active p-tolyl vinyl sulphoxide is accompanied by a low asymmetric a-induction not exceeding 10% (equation 336) . Addition of amines to vinyl sulphoxides proceeds in the same way giving )S-aminoethyl sulphoxides in good to quantitative yields depending on the substituents at the vinyl moiety When optically active p-tolyl vinyl sulphoxides are used in this reaction, diastereoisomeric mixtures are always formed and asymmetric induction at the p- and a-carbon atoms is 80 20 (R = H, R = Me) and 1.8 1 (R = Me, R = H), respectively (equation 337) ... 

The idea of Hoveyda with co-workers to employ their peptide ligands (e.g., 295) as chiral inductors in allylic substitutions with dialkylzincs turned out to be very rewarding.399-401 As a result of meticulous screening of numerous optically active ligands, copper salts, and substrates under various conditions, they achieved excellent results for aliphatic alkenes. Particularly, allylic substitution products with tertiary 297 and quaternary 299 carbon centers were obtained regioselectively and with 78-96% ee (Scheme 151).401... 

The advantages of the carbon tetrahalide-organophosphine-alcohol reaction to prepare halides are simplicity of experimental procedure good yields relatively mild, essentially neutral reaction conditions absence of allylic rearrangements. The reaction proceeds with inversion of configuration and is a useful simple device for converting optically active alcohols to chiral halides in high optical purity.12-22... 

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. 

In 2002, Trost and his co-workers reported a stereospecific ruthenium-catalyzed allylic alkylation reaction (Equation (58)). Treatment of an optically active allylic carbonate with carbon-centered nucleophiles in the presence of a ruthenium complex gives the corresponding allylic alkylated compounds with enantiomeric purity being completely maintained. Additionally, the regioselectivity is revealed not to be highly dependent on the nature of the starting carbonates. 

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... 

Regio- and diastereoselective rhodium-catalyzed tandem allylic alkylation of 71 with stabilized carbon and heteroatom nucleophiles 72 followed by the PK annulation by the same catalyst was described by Evans and co-workers. Alkylation of an optically active allylic alcohol carbonate 71 proceeds in a regio- and stereospecific manner successfully at 30 °C by 7r-acidic Rh(i) catalysts (Equation (41)). The resultant product then undergoes the PKR with the aid of the pre-existing catalyst under GO pressure at elevated temperature. ... 

Finally, the hybridization of the carbon atom also has a marked effect on its willingness to attach to the transition metal. Allyl or benzyl halides undergo oxidative addition faster than aromatic or vinyl halides. The least reactive are alkyl halides which require the use of nickel(O)9 complexes or highly active catalyst systems.10 If we start from an optically active substrate, then the oxidative addition usually proceeds in a stereoselective manner. 

The inclusion of the allyl moiety in an appropriate ring system led to the formation of a new, chiral quaternary carbon center (3.13.), By the use of optically active starting material, Mori and co-workers were able to control the stereochemistry of the new chiral centre (N.B. the chirality of the first centre was also set by a palladium catalysed reaction, the Tsuji-Trost allylation).17... 

An elegant example of a stereo relay in a nonrigid system employed a chiral vinyl lactone 430 For the relay to be completely successful (i) the ionization of the vinyl lactone must occur from one conformation, (ii) the intermediate ir-allylpalladium complex must retain its stereochemistry, and (iii) the nucleophile must attack regioselectively at the carbon of the allyl system distal to the incipient carboxylate. This distal transfer of chirality was achieved as shown in equation (346). This same process has been utilized in a synthesis of an optically active vitamin E side chain from D-glucose.431... 

Attempts to address the difficulty associated with the distance of the chirality in the Pd ligand to the site of C—C bond formation have been most fruitful. New chiral phosphine ligands containing an optically active functional group remote from the phosphines have been very effective, providing optical yields up to 52% in the case where the new chiral center is one carbon removed from the allyl ligand437 (c/. 10% optical parity obtained previously 434 equation 355). 

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