Absolute configuration activity

The same cannot be said about reactions with alkyl halides as substrates The conver Sion of optically active 2 octanol to the corresponding halide does involve a bond to the chirality center and so the optical purity and absolute configuration of the alkyl halide need to be independently established... 

X-ray analysis of an optically active oxaziridine substituted at nitrogen with the 1-phenylethyl group of known configuration led to the absolute configuration (+)-(2R,3R)-2-(5-l-phenylethyl)-3-(p-bromophenyl)oxaziridine of the dextrorotatory compound as expected, C-aryl and A-alkyl groups were trans to each other (79MI50800). 

Fragment B was synthesized in optically active form with the required absolute configuration through resolution of the epoxy acid C as shown below. 

Would you expect the 2-octanol formed by Sn2 hydrolysis of (-)-2-bromooctane to be optically active If so, what will be its absolute configuration and sign of rotation What about the 2-octanol formed by hydrolysis of racemic 2-bromooctane ... 

Discovery of Optically Active Molecules and Determination of Absolute Configuration... 

Raney cobalt is generally less effective than Raney nickel, but may be of use when the rupture of other bonds must be avoided. The important use of Raney nickel desulfurization for the structure determination of thiophenes and for the determination of the absolute configuration of optically active thiophene and benzene derivatives has been stressed earlier. 

The absolute configuration of the cycloaddition product obtained by the reaction of ketones with activated dienes catalyzed by (S)-t-Bu-BOX-Cu(II) (S)-21b points also to an intermediate in which the geometry around the central copper atom is square-planar similar to 26 above, and that the diene approaches the carbonyl functionality in an endo fashion. 

Thomson MOW Click Organic Intel active to assign absolute configurations using the Cahn-lngold-Prelog rules. 

The synthesis of key intermediate 12, in optically active form, commences with the resolution of racemic trans-2,3-epoxybutyric acid (27), a substance readily obtained by epoxidation of crotonic acid (26) (see Scheme 5). Treatment of racemic 27 with enantio-merically pure (S)-(-)-1 -a-napthylethylamine affords a 1 1 mixture of diastereomeric ammonium salts which can be resolved by recrystallization from absolute ethanol. Acidification of the resolved diastereomeric ammonium salts with methanesulfonic acid and extraction furnishes both epoxy acid enantiomers in eantiomerically pure form. Because the optical rotation and absolute configuration of one of the antipodes was known, the identity of enantiomerically pure epoxy acid, (+)-27, with the absolute configuration required for a synthesis of erythronolide B, could be confirmed. Sequential treatment of (+)-27 with ethyl chloroformate, excess sodium boro-hydride, and 2-methoxypropene with a trace of phosphorous oxychloride affords protected intermediate 28 in an overall yield of 76%. The action of ethyl chloroformate on carboxylic acid (+)-27 affords a mixed carbonic anhydride which is subsequently reduced by sodium borohydride to a primary alcohol. Protection of the primary hydroxyl group in the form of a mixed ketal is achieved easily with 2-methoxypropene and a catalytic amount of phosphorous oxychloride. 

Having retraced the efficient and elegant sequences of reactions that have led to the synthesi of key intermediates 11 and 12, we are now in a position to address their union and the completion of the total synthesis of erythronolide B. Taken together, intermediates 11 and 12 contain all of the carbon atoms of erythronolide B, and although both are available in optically active form of the required absolute configuration, racemic 11 and enantiomerically pure 12... 

Similar additions may be performed with the enamine 13. However, with 3-buten-2-one or methyl 2-propenoate Lewis acid catalysis is needed to activate the Michael acceptor chloro-trimethylsilane proved to be best suited for this purpose. A remarkable solvent effect is seen in these reactions. A change from THF to HMPA/toluene (1 1) results in a reversal of the absolute configuration of the product 14, presumably due to a ligand effect of HMPA235. 

Utilization of the Pfeiffer effect and outer-sphere complexation for the prediction of absolute configurations of optically active metal complexes. S. Kirschner and I. Bakkar, Coord. Chem. Rev., 1982,43, 325-335 (27). 

Thus, the enantiomeric contents in a pair of sulphoxides can be determined by the NMR chemical shifts in the methine or methylene protons in the two diastereomeric complexes which are stabilized by the hydrogen bond between the hydroxyl and the sulphinyl groups147-151 (Scheme 13). Similarly, the enantiomeric purity and absolute configurations of chiral sulphinate ester can be determined by measuring the H NMR shifts in the presence of the optically active alcohols152. 

Optically active 2,2,2-trifluorophenylethanol, when used as NMR solvent, causes enantiomeric spectral dissimilarities for chiral episulphoxides the relative field positions of non-equivalent NMR resonances are analyzed with respect to the absolute configuration of the solvated compounds220. 

In a similar way to the aminolysis of the P-N bond mentioned above (Scheme 9), alcoholysis of phosphinous amides leads to the alkyl esters of the respective phosphinous acids [30, 121]. This reaction occurs with inversion of the absolute configuration of the phosphorus atom, and has been used in a synthetic sequence leading to optically active tertiary phosphanes 22 [122] (Scheme 23). 

Another problem that required solving was the moderate yield obtained in the cyclopropanation reaction when only one equivalent of styrene was used. By increasing the amount of styrene up to its use as the reaction solvent, a noticeable effect on the selectivities was observed when laponite was used as the support [58]. The active role of the clay support was definitely estabhshed when the results in homogeneous and heterogeneous phases were compared (Table 9). These effects involved the reversal of the trans preference in solution to the cis preference with the laponite-supported catalyst in styrene, and also a reversal in the absolute configuration of the major cis enantiomer ob-... 

---