Cis-racemates

The reaction is also stereospecific because different stereoisomers give stereochemically different products, e.g. CIS— racemic and transmeso. Because of this stereospecificity, the intermediate cannot be the free carbocation CH,CHBrCHCH,. The same carbocation would arise from either cis-or /rans-2-butene, and the product distribution from both reactants would be identical. 

J. N. Levy, and M. Stukus, Side chain selectivity and kinetics of penidllin G amidase in acylating a cis-racemic / -lactam intermediate in the synthesis of Loracarbef, New J. Chem. 1994, 38, 425 434. 

The residue was dissolved in anhydrous ether (1 L) and the resulting solution treated with gaseous hydrogen chloride to yield a white precipitate, containing about 70% cis-racemate and 30% tras-racemate of N-methyl-4-(3,4-dichlorophenyl)-l,2,3,4-tetrahydro-l-naphthalenamine hydrochloride. 

The HCI salt cis-racemate and trans-racemate of N-methyl-4-(3,4-dichlorophenyl)-l,2,3,4-tetrahydro-l-naphthalenamine hydrochloride, was dissolved in hot methanol (2 L). Upon addition of ether (1200 ml) and cooling overnight, cis-(lS)(lR)-N-methyl-4-(3,4-dichlorophenyl)-l,2,3,4-tetrahydro-l-naphthalenamine hydrochloride precipitated (47 g, melting point 290°-291°C). The supernatant was evaporated under vacuum to dryness and the residue triturated with acetone. The triturated residue (ca. 90% cis-racemate, 10% trans-racemate) was recrystallized from methanol ether (1 1) to yield another 20 g of the same product. The total yield of cis-(lS)(lR)-N-methyl-4-(3,4-dichlorophenyl)-l,2,3,4-tetrahydro-l-naphthalenamine hydrochloride was 67g, 68% yield melting point 289°-290°C. 

Early studies from the Pfizer laboratories had revealed that compounds from a series of mzn.s-l-amino-4-phenyl-tetralins possessed potent norepinephrine (NE) uptake blocking activity. The activity was highly specific for the (1/ , 4S)-enantiomer and was confined to the trans derivatives. The corresponding (IS, 4/ )-enantiomer was much less active and the diastereomeric cis racemates were inactive at blocking NE uptake. It was subsequently shown that many compounds from the diastereomeric cis senes were unexpectedly potent and selective inhibitors of serotonin (5-HT) uptake, thus differentiating these compounds from the trans compounds. One of these compounds, sertraline (5), was originally discovered as a racemic mixture. Resolution showed that the (+)-enantiomer was several times more selective for 5-HT uptake blocking activity than the (-)-isomer. The (+)-enantiomer was subsequently shown to possess the in vivo behavioral effects expected of a potent and selective 5-HT blocker. Thus, as opposed to... 

Dimethyl-l,4-dioxan-23 dione (Lactide) [cis-RSJiS-( ) 615-95-2, cis-RJi-( ) 95-96-5, cis-S,S-(-) 4511-42-6 7M 144.1. This is the cyclic dilactone of lactic acid. The )-cis-racemate has been distilled with b 142 /8mm the distillate which solidifies gives yellow needles on recrystaUisation from EtOH with m 128", from Et20 with m 129", or CHCI3 with m 126", Vmax 1720-1740 cm >. It hydrolyses in cold H2O. [Carothers et al. y Am Chem Soc 54 772 1932], A trans-form (probably has been reported... 

Yamazaki et al. resolved the Boc-protected cis racemate [78]. Treatment of the racemic c/s-2-ACPC with di-te/7-butyl dicarbonate resulted in the A-Boc-protected derivative, which was mixed with (-)-ephedrine. The resulting salt was fractionally crystallized from the ethyl acetate/diethyl ether solvent system. Treatment with sodium hydrogensulfate and removal of the Boc group with trifluoracetic acid (TFA) gave the (+)-(15,2/ ) enantiomer. 

Tacticity arises in these polymers from the relative orientation of the five membered rings in the polymer backbone as shown in structure (32). Thus, depending on the configuration of the adjacent double bond c/ -syndiotactic cis racemic, c ), cis isotactic cis meso, c ), trans syndiotactic trans racemic, t ) and /raw -isotactic trans meso, /m) dyads result. 

In the same way the cis racemate II of the presently most active pyrethroid known, the ester of cis-Z-cyhalothrinic acid and cyfluthrin-alcqhol is obtained [860, 861]. 

ROMP of 4-methylcyclopentene leads to the formation of a polymer with four different configurations, cis-meso, cis-racemic, trans-racemic, trans-meso stereochemical, owing to the relative positioning of the methyl substituents. ... 

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