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Prochiral

Chiral aluminium hydride for the asymmetric reduction of prochiral ketones... [Pg.49]

Aldehydes are "prochiral", thus addition of an organometallic reagent to an aldehydes may be stereoselective,... [Pg.92]

A highly diastereoselective alkcnylation of c/s-4-cyclopentene-l,3>diols has been achieved with 0-protected (Z)-l-iodo-l-octen-3-ols and palladium catalyst (S. Torii, 1989). The ( )-isomers yielded 1 1 mixtures of diastcrcomcric products. The (Z)-alkenylpalladium intermediate is thought to undergo sy/i-addition to the less crowded face of the prochiral cyclopentene followed by syn-elimination of a hydropalladium intermediate. [Pg.43]

In cases where Noyori s reagent (see p. 102f.) and other enantioselective reducing agents are not successful, (+)- or (—)-chlorodiisopinocampheylborane (Ipc BCl) may help. This reagent reduces prochiral aryl and tert-alkyl ketones with exceptionally high enantiomeric excesses (J. Chandrasekharan, 1985 H.C. Brown, 1986). The initially formed boron moiety is usually removed hy precipitation with diethanolamine. Ipc2BCl has, for example, been applied to synthesize polymer-supported chiral epoxides with 90% e.e. from Merrifield resins (T. Antonsson, 1989). [Pg.108]

Achiral molecules which can be converted to chiral molecules by the chemical change of one atom — substitution on an sp -atom or addition on an sp -atom — are called prochiral molecules (Y. Izumi, 1977). The atom involved is a prochiral centre. Pairs of atorns or groups... [Pg.359]

Analogous definitions and designations apply to molecules containing a chiral centre and a prochiral tetrahedral or trigonal centre. The plane containing the chiral and prochiral centres is called a diastereo-zeroplane (Y. Izumi, 1977). [Pg.360]

The prochiral meso form of 2-cyclopenlen-1,4-diol (101) reacts with the (Z)-alkenyl iodide 102 to give the 3-substituted cyclopentanone 103 with nearly complete diastereoselectivity (98 2)[92], The reaction is used for the synthesis of prostaglandin. The alkenyl iodide 102 must be in the Z form in order to obtain the high diastereoselectivity. The selectivity is low when the corresponding (Z)-alkenyl iodide is used[93]. [Pg.143]

In this example addition to the double bond of an alkene converted an achiral mol ecule to a chiral one The general term for a structural feature the alteration of which introduces a chirality center m a molecule is prochiral A chirality center is introduced when the double bond of propene reacts with a peroxy acid The double bond is a prochi ral structural unit and we speak of the top and bottom faces of the double bond as prochiral faces Because attack at one prochiral face gives the enantiomer of the com pound formed by attack at the other face we classify the relationship between the two faces as enantiotopic... [Pg.297]

The pro in prochiral means before or in advance of in roughly the same way as in proactive... [Pg.297]

We can view this reaction as the replacement of one or the other of the two methylene protons at C 2 of butane These protons are prochiral atoms and as the red and blue protons m the Newman projection indicate occupy mirror image environments... [Pg.299]

The double bond m 2 methyl(methylene)cyclohexane is prochiral The two faces however are not enantiotopic as they were for the alkenes we discussed m Section 7 9 In those earlier examples when addition to the double bond created a new chirality cen ter attack at one face gave one enantiomer attack at the other gave the other enantiomer In the case of 2 methyl(methylene)cyclohexane which already has one chirality center attack at opposite faces of the double bond gives two products that are diastereomers of each other Prochiral faces of this type are called diastereotopic... [Pg.309]

FIGURE 17 14 (a) Binding sites of enzyme discriminate between prochiral faces of substrate One prochiral face can bind to the enzyme better than the other (b) Reaction attaches fourth group to substrate producing only one enantiomer of chiral product... [Pg.735]

Prochiral (Section 7 9) The capacity of an achiral molecule to become chiral by replacement of an existing atom or group by a different one... [Pg.1291]

Among chiral dialkylboranes, diisopinocampheylborane (8) is the most important and best-studied asymmetric hydroborating agent. It is obtained in both enantiomeric forms from naturally occurring a-pinene. Several procedures for its synthesis have been developed (151—153). The most convenient one, providing product of essentially 100% ee, involves the hydroboration of a-pinene with borane—dimethyl sulfide in tetrahydrofuran (154). Other chiral dialkylboranes derived from terpenes, eg, 2- and 3-carene (155), limonene (156), and longifolene (157,158), can also be prepared by controlled hydroboration. A more tedious approach to chiral dialkylboranes is based on the resolution of racemates. /n j -2,5-Dimethylborolane, which shows excellent enantioselectivity in the hydroboration of all principal classes of prochiral alkenes except 1,1-disubstituted terminal double bonds, has been... [Pg.311]

Asymmetric Hydroboration. Hydroboration—oxidation of (Z)-2-butene with diisopinocampheylborane was the first highly enantioselective asymmetric synthesis (496) the product was R(—)2-butanol in 87% ee. Since then several asymmetric hydroborating agents have been developed. Enantioselectivity in the hydroboration of significant classes of prochiral alkenes with representative asymmetric hydroborating agents is shown in Table 3. [Pg.322]

Table 3. Enantioselectivity in the Hydroboration of Prochiral Alkenes with Various Hydroborating Agents ... Table 3. Enantioselectivity in the Hydroboration of Prochiral Alkenes with Various Hydroborating Agents ...
An efficient general synthesis of a-chiral (Z)- and (H)-a1kenes ia high enantiomeric purity is based on the hydroboration of alkynes and 1-bromoaIkynes, respectively, with enantiomericaHy pure IpcR BH readily available by the hydroboration of prochiral alkenes with monoisopiaocampheylborane, followed by crystallization (519). [Pg.324]

In the earlier, longer approach to (Z)-and (E)-alkenes, ThxR BH was used iastead of IpcR BH. It is also possible to prepare a-chiral acetylenes and alkanes by this method (76,520). In a shorter synthesis of a-chiral alkynes, a prochiral disubstituted (Z)-a1kene is hydroborated with... [Pg.324]

Efficient enantioselective asymmetric hydrogenation of prochiral ketones and olefins has been accompHshed under mild reaction conditions at low (0.01— 0.001 mol %) catalyst concentrations using rhodium catalysts containing chiral ligands (140,141). Practical synthesis of several optically active natural... [Pg.180]

The strategy of the catalyst development was to use a rhodium complex similar to those of the Wilkinson hydrogenation but containing bulky chiral ligands in an attempt to direct the stereochemistry of the catalytic reaction to favor the desired L isomer of the product (17). Active and stereoselective catalysts have been found and used in commercial practice, although there is now a more economical route to L-dopa than through hydrogenation of the prochiral precursor. [Pg.165]

Fig. 4. Schematic representation of energy profiles for the pathways for the hydrogenation of a prochiral precursor to make L-dopa (19). The chiral... Fig. 4. Schematic representation of energy profiles for the pathways for the hydrogenation of a prochiral precursor to make L-dopa (19). The chiral...
The situation is different if the substrate is a prochiral or meso compound. Since these molecules have a center or plane of symmetry the binding of pro-S or pro-R forms is equivalent. The chirahty appears only as a result of the transformation. Hence, at least theoretically, the compound can be converted to one enantiomer quantitatively. [Pg.332]

It is generally beheved that selectivity of hydrolytic enzymes strongly depends on the proximity of the chiral center to the reacting carbonyl group, and only a few examples of successful resolutions exist for compounds that have the chiral center removed by more than three bonds. A noticeable exception to this rule is the enantioselective hydrolysis by Pseudomonasfluorescens Hpase (PEL) of racemic dithioacetal (5) that has a prochiral center four bonds away from the reactive carboxylate (24). The monoester (6) is obtained in 89% yield and 98% ee. [Pg.333]

Mono cylDiols. Enzymatic synthesis of chiral monoacyl diols can be carried out either by direct enzymatic acylation of prochiral diols or by hydrolysis of chemically synthesized dicarboxylates. [Pg.335]

A number of examples of monoacylated diols produced by enzymatic hydrolysis of prochiral carboxylates are presented in Table 3. PLE-catalyzed conversions of acycHc diesters strongly depend on the stmcture of the substituent and are usually poor for alkyl derivatives. Lipases are much less sensitive to the stmcture of the side chain the yields and selectivity of the hydrolysis of both alkyl (26) and aryl (24) derivatives are similar. The enzyme selectivity depends not only on the stmcture of the alcohol, but also on the nature of the acyl moiety (48). [Pg.335]

In contrast to the hydrolysis of prochiral esters performed in aqueous solutions, the enzymatic acylation of prochiral diols is usually carried out in an inert organic solvent such as hexane, ether, toluene, or ethyl acetate. In order to increase the reaction rate and the degree of conversion, activated esters such as vinyl carboxylates are often used as acylating agents. The vinyl alcohol formed as a result of transesterification tautomerizes to acetaldehyde, making the reaction practically irreversible. The presence of a bulky substituent in the 2-position helps the enzyme to discriminate between enantiotopic faces as a result the enzymatic acylation of prochiral 2-benzoxy-l,3-propanediol (34) proceeds with excellent selectivity (ee > 96%) (49). In the case of the 2-methyl substituted diol (33) the selectivity is only moderate (50). [Pg.336]


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1.3- Dienes, prochiral

3- hydroxyglutaronitrile, prochiral

Acetophenone derivatives, prochiral

And prochiral centers

Asymmetric Hydrogenation of Prochiral Allylic Alcohols

Asymmetric Hydrogenation of Prochiral Olefins

Asymmetric Hydrogenation of Prochiral Olefins by Rhodium-DuPhos Catalysts

Asymmetric Reduction of Prochiral Ketimines

Asymmetric Reduction of Prochiral Ketones Catalyzed by Oxazaborolidines

Asymmetric allylation prochiral nucleophiles

Asymmetric oxidation of prochiral sulfides

Asymmetric reactions prochiral nucleophiles

Asymmetric reduction of a prochiral ketone (chloroacetophenone)

Asymmetric reduction prochiral ketones

Asymmetrization of Prochiral Compounds

Asymmetrization of Prochiral Dicarboxylates Single-Step Process

Carboxylic esters prochiral

Cascade enantioselective reduction, prochiral

Chirality and prochirality

Chirality prochiral center

Chirality prochiral substrates

Chirality prochirality

Citrate prochiral centers

Citrate, prochirality

Citric acid prochirality

Configuration prochiral

Cyclohexanone prochiral 4-substituted

Definition of a Prochiral Object

Deprotonation prochiral substrates

Desymmetrization prochiral diester

Diacetates, prochiral

Diacetates, prochiral desymmetrization

Dialkoxysilanes, prochiral

Diols, desymmetrization prochiral

Enamides prochiral

Enantioselective Hydrogenation of Prochiral Substrates

Enantioselective hydrogenations of prochiral olefins

Enantioselective prochiral enol carbonates

Enantioselectivity reduction of prochiral ketones

Enolates prochiral

Enones prochiral. conjugate addition reactions

Enzyme prochiral centers

Enzyme prochiral substrate, binding

Enzyme resolution, prochiral diester

Ethers prochiral ketoxime

For prochiral elements

From prochiral substrates

Hydrogen atoms, prochiral pairs

Hydrogenation of prochiral olefins

Hydrogenation prochiral olefins

Imines prochiral

Ketenes, prochiral

Ketones prochiral aryl alkyl

Ketones prochiral, reduction

Lipases prochiral compounds

Nerol, prochiral allylic alcohol

Nitroalkenes prochiral

Nitrogen ligands prochiral

Nucleophilic prochiral carbonyl compound

Olefin complexes containing prochiral

Olefinic substrates, prochiral

Olefins, prochiral

Phosphates prochiral

Phosphine oxides prochiral

Phosphorus prochiral

Plane sites prochiral

Pro-S prochirality center

Prochiral Environments

Prochiral Molecules Interacting with Chiral Surfaces

Prochiral Molecules, Enantiotopic Groups and Faces

Prochiral Substituents at the Radical Center

Prochiral acetophenone

Prochiral acyclic

Prochiral acylated diols

Prochiral alcohols

Prochiral alkenes

Prochiral alkenes dioxirane epoxidation

Prochiral alkenes, asymmetric hydrosilylation

Prochiral alkenes, epoxidation

Prochiral alkenes/olefins

Prochiral allylic alcohols

Prochiral anhydrides

Prochiral aromatic molecule

Prochiral asymmetric hydrogenation

Prochiral asymmetrization

Prochiral atoms

Prochiral carbon

Prochiral carbonyl compounds

Prochiral carbonyl groups

Prochiral carbonyl groups asymmetric addition

Prochiral carbonyls

Prochiral carboxylic acid

Prochiral centers

Prochiral centers, definition

Prochiral centre

Prochiral chromium complexes

Prochiral compound

Prochiral compounds Michael addition

Prochiral compounds alkylations

Prochiral compounds allylations

Prochiral compounds amination

Prochiral compounds ketones, asymmetric reductive

Prochiral compounds reduction

Prochiral compounds, asymmetric

Prochiral compounds, asymmetric desymmetrization

Prochiral cyclic

Prochiral definition

Prochiral desymmetrization

Prochiral diaryl ketones

Prochiral dicarboxylates

Prochiral dicarboxylic acid diesters

Prochiral dicarboxylic acid esters

Prochiral diester malonates

Prochiral diesters

Prochiral dihydrosilanes

Prochiral diketones

Prochiral diol

Prochiral diol asymmetrization

Prochiral diol diacetates

Prochiral diol, stereoselective oxidation

Prochiral diols oxidation

Prochiral diols, enantioselective acylation

Prochiral electrophiles

Prochiral enolate

Prochiral enolate equivalents

Prochiral esters

Prochiral face

Prochiral glutarates

Prochiral groups

Prochiral guest

Prochiral heteroaromatics

Prochiral imine

Prochiral imines, asymmetric hydrosilylation

Prochiral ketone, oxazaborolidine

Prochiral ketone, oxazaborolidine reduction

Prochiral ketones

Prochiral ketones chiral alchohols from

Prochiral ketones reduction with yeast

Prochiral ketones with cofactor

Prochiral ketones, asymmetric

Prochiral ketones, asymmetric hydrosilylation

Prochiral malonates

Prochiral model substrates

Prochiral molecule

Prochiral molecules interaction with chiral

Prochiral monomers

Prochiral naphthalene rings

Prochiral naphthalene rings asymmetric additions

Prochiral nitroalkanes

Prochiral non-equivalence

Prochiral nucleophiles

Prochiral nucleophiles enantioselective allylation

Prochiral nucleophiles, allylation

Prochiral nucleophiles, nucleophilic substitution

Prochiral nucleophiles, nucleophilic substitution asymmetric allylation

Prochiral nucleophilic addition

Prochiral nucleophilic addition reactions

Prochiral olefins stereoselective olefin

Prochiral oximes

Prochiral oxoamide

Prochiral phosphorus centers

Prochiral precursors

Prochiral propanediol acetate hydrolysis

Prochiral protons, assignment

Prochiral radicals

Prochiral reagent

Prochiral relationships

Prochiral stereoselective acylation

Prochiral stereospecificity

Prochiral structure

Prochiral substances

Prochiral substrates, asymmetric

Prochiral substrates, reactions

Prochiral sulfides asymmetric oxidation

Prochiral sulfides described

Prochiral sulfides enantioselective oxidation

Prochiral surfaces

Prochiral synthesis

Prochiral systems

Prochiral unsaturated carboxylic acid

Prochirality

Prochirality

Prochirality assignment

Prochirality centre

Prochirality naturally occurring molecules and

Prochirality re descriptor for

Prochirality si descriptor for

Prochirality, defined

Prochirality, definition

Prochirality: terminology

Prochirality’center

Re prochirality

Reaction of prochiral substrates

Reactions of solvate dihydrides with prochiral substrates

Reactions with Prochiral Carbonyl Compounds

Reactions with Prochiral Ketenes to give Dissymmetric Allenes

Reduction of Labeled Prochiral Carbonyl Compounds and Oximes

Reduction of prochiral ketones

Reduction prochiral aryl alkyl

Si prochirality

Stereochemistry prochiral centers

Stereochemistry prochiral groups

Stereospecificity prochiral centers

Substitution reactions prochiral nucleophiles

Substrate, prochiral

Substrate, prochiral desymmetrization

Sulfides prochiral

Trigonal prochiral centers

Yeast prochiral ketone

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