Erythro compounds

The erythro compound shows little or no kinetic isotope effect, but the threo compound has a moderate one, H/fcD 2-3-3-3, for both syn and anti processes. This suggests that an E2 process is involved. Eliminations from the cyclic bromides may produce trans alkenes by syn eliminations or by anti eliminations, if n 8 in(189). 

Chloro-2-butyl Tellurium Trichloride15 A 100 ml flask fitted with a magnetic stirrer is flushed with nitrogen, charged with 1.67 g (6.2 mmol) of freshly sublimed tellurium tetrachloride, 0.36 g (6.4 mmol) of (Z)-2-butcnc, and 20 ml of ethanol-free chloroform, and immersed in an ice bath. The mixture is stirred for 3 h, filtered, and the filtrate is evaporated yield 1.35 g (67%), mixture of threo (80%) and erythro (20%) isomers. The mixture is recrystallized to yield the pure threo compound m.p. 107°. The erythro compound was not obtained in an isomerically pure state. 

To a two-necked round-bottomed flask (50 mL) equipped with a magnetic stirrer, rubber septum and under a nitrogen atmosphere, add the erythro compound (1/ S,2S/ )-2-diphenylphosphinoyl-1-phenylbutan-1-ol (800 mg, 2.28 mmol, see Protocol 7) and dimethylformamide (25 mL). 

The erythro compound, ET, gave the erythro acetate, EA, with almost quantitative retention of optical activity. On the other hand, the optically active three tosylate, TT, gave racemic threo acetate, TA. The explanation for these striking results is given in terms of the different, bridged carbonium ions formed in each case ... 

Further supporting evidence is provided by the observation that, after the acetolysis has been allowed to go to 50 per cent completion, the remaining erythro compound, ET, is optically pure, while the remaining threo compound, TT, is racemized. This is considered as evidence also for the intermediate formation of an fintimate ion pair, since it is found that tlio reactions are not inhibited by even high concentrations of HOTs. Such a test is not very meaningful, however, since HOTs is extraordinarily little ionized in the low dielectric, acetic acid. 

Note, that because of the retention of configuration in the bromonium ion, the same erythro compound is obtained independently of the point of attachment of the entering Br ion. 

Modified T) -titanium compounds have been prepared from exocyclic dienes. The compound (123, n = 3) is an example it is prepared (equation 47) by addition of Bu MgCl to a solution of 1-vinylcyclopen-tene (122, n = 3) and (T) -C5H5)2TiCl, Its reaction with propanal takes place regiospecifically at the carbon atom belonging to the cycle, in 86% yield, affording the sole erythro compound (124, n = 3) (equation... 

In contrast to the erythro-compound 34 (OR = a-OEt), the reaction of the a-D-r/nw-enoside leads preferentially to alkylation at C-2 because of increased steric interaction between the nucleophile and the ra-located 6-acetoxymethyl group. All reactions proceed with clean inversion of configuration to furnish the C-branched sugars 39 and 4063. 

Studies of the optical rotatory dispersion of polyhydroxyalkyl-quinoxalines have been made. In methanol or in dimethylsulfoxide, negative Cotton effects centered at 315 nm are associated with R chirality at C-T. The same correlation holds for the O-acetyl derivatives of polyhydroxyalkylquinoxalines. Compounds with threo relationship at C-1 and C-2 (A,B,C) have higher amplitude Cotton effects than erythro compounds (D, E). Quinoxalines with threo relationship at C-1 and C-2 also have higher rotatory power at long wavelength. Acetylation destroys the difference between threo and erythro compounds. ... 

Sol 3. The syn character of pyrolytic eliminations has been demonstrated in many ways. For example, pyrolysis of erythro and threo isomers of 1-acetoxy-2-deutero-l,2-diphenylethane gave in each case frans-stilbene as a major product, but the stilbene from the erythro compound retained nearly all its deuterium, whereas the stilbene from the threo compound had lost most of its deuterium. Either the hydrogen or deuterium could be syn to the acetoxy group, but the preferred conformations are those in which the phenyl groups are as far removed from each other as possible. 

Amino-2-deoxytetritol derivatives were also synthesised from allylic alcohols via formation of the trichloroacetamidate (20). lodocyclisation of (20) to (21) led ultimately to the ( )-erythro compound (22) whilst thermal [3,3]-sigmatropic rearrangement of (20) to the allylic trichloroacetamide (23) prior to cycli-... 

Such hydroxylated fatty acids in the form of less polar derivatives, for example isopropylidene, TMS ether or methoxy compounds, have been used in conjunction with mass spectrometry to locate the positions of the original double bonds (see Chapter 7). Because the isopropylidene derivatives of threo and erythro compounds are separable by GC, the configuration of the original double bonds can also be established [572,985]. 

They can be separated into three groups on layers of silica gel G impregnated with 2% boric acid, i.e. saturated dihydroxy-, unsaturated dihydroxy (with a trans double bond in position 4) and trihydroxy bases, with chloroform-hexane-methanol (5 5 2 by volume) as the mobile phase [465]. When acidic hydrolysis procedures are utilised in the preparation of the bases, unnatural threo- somers of the unsaturated dihydroxy bases are found just below the natural erythro compounds on the TLC plate. Each of the fractions separated by TLC can be recovered from the adsorbent by elution with chloroform-methanol (2 1, v/v), but the eluate should be washed with one quarter the volume of water to remove boric acid which is also eluted. If need be, the bases can be further resolved by silver ion TLC [462] or by HPLC in the reversed-phase mode (reviewed elsewhere [168]). It is possible that HPLC in the adsorption or silver ion modes could also contribute to the problem of analysis, but these do not appear to have been tried. 

Kibby et al. studied the reactions of threo- and 3ianti elimination was the preferred mode over alumina and syn elimination over hydroxyapatite. Thomke and Noller determined the ratio of syn/anti ratio of elimination over various phosphates from the same reactants. " The ratio was calculated to be 85/15 with Ca3(P04)2, 70/30 with CaHP04 and Ba3(P04)2 and 45/55 with AIPO4. 

In this case threo-sphingosine appeared more effective than the erythro compound. The product of the reaction has not been unequivocally characterized. 

Malspeis and Hung [85] investigated the isomeric N-nitro-soephedrine (erythro compound) and N-nitrosopseudoephedrine (threo compound) ... 

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