Erythro and Threo

Sometimes the terms erythro and threo are used to specify fee relative configuration of two adjacent stereogenic centers. The terms are derived fom fee sugars erythrose and threose. The terms were originally defined such feat a Fischer projection formula in which two adjacent substituents were on the same side was fee erythro isomer and feat in whidi the substituents were on opposite sides was the threo isomer. 

Table 2. Dehydrofluorination of erythro- and threo-a-Bromo-a -fluorosucdtiic Acids by Sodium Deuteroxide in Deuterium Oxide [35]...

Eor the elimination of trimethylamine and water from the erythro- and threo-isomer of trimethyl-1,2-diphenylpropylammonium iodide 6 and 7 respectively, by treatment with sodium ethoxide, a stereospecific -elimination has been found to take place thus supporting a E2-mechanism. Erom the -isomer... 

The bromination products, dibromide in methylene chloride and methoxybromide in methanol, are a mixture of erythro- and threo-diastereoisomers, obtained in a ratio, Erythro/Threo = 70 / 30, which does not depend on the substituents or on the solvent. As expected, the reaction in the protic solvent is fiilly regioselective, i.e. methanol only traps the intermediate... 

For many open-chain compounds, prefixes are used that are derived from the names of the corresponding sugars and that describe the whole system rather than each chiral center separately. Two such common prefixes are erythro- and threo-, which are applied to systems containing two stereogenic carbons when two of the groups are the same and the third is different. The erythro pair has the identical Y Y Y Y... 

A study of the decomposition in basic media of the erythro- and threo-isomers of the /8-hydroxyphosphonate (169) showed that the first step in the phosphonate olefin synthesis is reversible and that the diastereo-isomers of (169) can also interconvert directly, presumably via the a-car-banion. 

In the synthesis shown in Scheme 13.15, racemates of both erythro- and threo-juvabione were synthesized by parallel routes. The isomeric intermediates were obtained in greater than 10 1 selectivity by choice of the E- or Z-silanes used for conjugate addition to cyclohexenone (Michael-Mukaiyama reaction). Further optimization of the stereoselectivity was achieved by the choice of the silyl substituents. The observed stereoselectivity is consistent with synclinal TSs for the addition of the crotyl silane reagents. 

Bardet, M. Robert, D. Lundquist, K. von Unge, S. Distribution of erythro and threo forms of different types of P-O-4 structures in aspen lignin by carbon-13 NMR using the 2D inadequate experiment. Magn. Reson. Chem. 1998, 36, 597-600. 

Doublet observed (ca. 0.1 ppm separation) due to the presence of erythro and threo diastereomers. 

During the asymmetric synthesis of erythro and threo a-substituted 3-amino esters, the dimethylbinaphthyl moiety (28 in Fig. 4.5) was removed using transfer hydrogenolysis. 

Double bonds present along a polymer chain are stereoisomeric centers, which may have a cis or trans configuration. Polymers of 1,3-dienes with 1,4 additions of the monomeric units contain double bonds along the chains and may contain up to two stereoisomeric tetrahedral centers. Stereoregular polymers can be cis or trans tactic, isotactic or syndiotactic, and diisotactic or disyndio-tactic if two stereoisomeric tetrahedral centers are present. In the latter case erythro and threo structures are defined depending on the relative configurations of two chiral carbon atoms.1... 

Selenosulfonylation of olefins in the presence of boron trifluoride etherate produces chiefly or exclusively M products arising from a stereospecific anti addition, from which vinyl sulfones can be obtained by stereospecific oxidation-elimination with m-chloroper-benzoic acid134. When the reaction is carried out on conjugated dienes, with the exception of isoprene, M 1,2-addition products are generally formed selectively from which, through the above-reported oxidation-elimination procedure, 2-(phenylsulfonyl)-l,3-dienes may be prepared (equation 123)135. Interestingly, the selenosulfonylation of butadiene gives quantitatively the 1,4-adduct at room temperature, but selectively 1,2-adducts at 0°C. Furthermore, while the addition to cyclic 1,3-dienes, such as cyclohexadiene and cycloheptadiene, is completely anti stereospecific, the addition to 2,4-hexadienes is nonstereospecific and affords mixtures of erythro and threo isomers. For both (E,E)- and ( ,Z)-2,4-hexadienes, the threo isomer prevails if the reaction is carried out at room temperature. 

From a historical standpoint, the Zimmerman-Traxler study on the stereochemical aspects of the Ivanov reaction is of considerable significance (22). Their investigation revealed that the magnesium enediolate 19a, upon condensation with benzaldehyde (Et2 O, reflux 5 hr), afforded the erythro and threo acids 20E and 20T, respectively, in a 24 76 ratio (eq. [13]). In the analysis of plausible transition states, both chair A and boat B geometries were considered. Zimmerman and Traxler concluded that the major diastereomer 20T could... 

Related reactions, catalyzed by tetra-n-butylammonium fluoride (TBAF), have been reported (74). Under the influence of 5 to 10 mol % of TBAF (THF, -78°C), enolsilane 75 afforded the erythro and threo adducts 76E and 76T whose ratios were time dependent (5 min, E T =1 2 10.5 hr, E T =1 3) (74). The reaction of enolsilane 77 at various temperatures has also been reported (2). At -78 C (1 hr) complete kinetic erythro diastereoselection was observed under the conditions reported by Noyori (74), but at higher temperatures product equilibration was noted (2). It is significant that the kinetic aldol condensation of this tetraalkylammonium enolate exhibits complete erythro selection as noted for the analogous lithium derivative. 

The first asymmetric procedure consists of the addition of R2Zn to a mixture of aldehyde and enone in the presence of the chiral copper catalyst (Scheme 7.14) [38, 52]. For instance, the tandem addition of Me2Zn and propanal to 2-cyclohexenone in the presence of 1.2 mol% chiral catalyst (S, R, R)-1S gave, after oxidation of the alcohol 51, the diketone 52 in 81% yield and with an ee of 97%. The formation of erythro and threo isomers is due to poor stereocontrol in the aldol step. A variety of trans-2,3-disubstituted cyclohexanones are obtained in this regioselective and enantioselective three-component organozinc reagent coupling. 

Dihydroxyacetone was exposed to boiling aqueous pH 4.5 buffer the products resulting were considerably more complex than those attributable to simple dehydration. The yields of the twenty compounds isolated from the mixture ranged from 0.03 to 1.2%. The major products of this acidic reaction were 3-hydroxy-2,5-hexanedione, and erythro- and threo-3,4-dihydroxy-2,5-hexanedione. These apparent reduction products may have been formed by an aldol/retro-aldol/re-aldol sequence involving acetol. 

G. aabbitt In the same spectrum, you showed pairyof methylene signals and attributed the doubling to erythro and threo structures of the H-Cl units. Three units were pictured an ethylene unit in the center with H-Cl containing units on either end. It is possible that both ends can be erythro, or both ends can be threo, or be mixed. Yet, only doublets are obtained. It seems to me there should be more multiplicity in the methylene signals. 

These monomers produce a single disyndiotactic polymer characterized by alternating erythro and threo relationships between adjacent substituents, 18 or 19. In such a polymer it is not possible—unless one turns to selective isotopic labeling—to determine whether the erythro and threo relationship refers to the substituents A and B of the same monomer unit or to those of two successive monomeric units. 

The combination of cis-trans isomerism with iso-syndio and erythro-threo dispositions gives complex stractures as exemplified by the 1,4 polymers of 1-or 4-monosubstituted butadienes, such as 1,3-pentadiene (72, 73), and 2,4-pentadienoic acid (74, 75) and of 1,4-disubstituted butadienes, for example, sorbic acid (76). This last example is described in 32-35 (Scheme 6, rotated Fischer projection). Due to the presence of three elements of stereoisomerism for each monomer unit (two tertiary carbons and the double bond) these polymers have been classed as tritactic. Ignoring optical antipodes, eight stereoregular 1,4 structures are possible, four cis-tactic and four trans-tactic. In each series (cis, trans) we have two diisotactic and two disyndiotactic polymers characterized by the terms erythro and threo in accordance with the preceding explanation. It should be noted that here the erythro-threo relationship refers to adjacent substituents that belong to two successive monomer units. 

By the presence of cyclic monomer units obtained, for example, from cyclic olefins (benzofuran, indene, etc.) (58, 254). The erythro- and threo-diisotactic stractures (26, 27 or in a different representation 77, 78) are chiral. If B is equal to A (cyclobutene or analogous monomers) only the threo-diisotactic structure 27 is chiral. 

All four diisotactic polymers (cis and trans, erythro and threo) are chiral and possess optical activity. Each of the four disyndiotactic polymers possesses a mirror glide plane and is achiral. For symmetric 1,4-disubstituted 1,3-butadienes (R = R ), only the cis and transthreo-diisotactic structures are chiral. Each of the erythrodiisotactic and threodisyndiotactic polymers has a mirror glide plane. Each of the erythrodisyndiotactic polymers has a mirror glide plane. 

Little is known about the R/S isomerism (i.e., erythro and threo ditactic structures are possible) at the stereocenters that result from double-bond polymerization. Cycloheptene and higher cycloalkenes undergo only ROMP double-bond polymerization does not occur because the larger rings can accommodate the double bond without being highly strained. 

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