Circular Dichroism of Tricarbonyl(diene)iron Complexes. The Octant Rule Applied to Ketones Perturbed by Remote Fe(CO)3 Groups. Crystal Structure of (±)-Tricarbonyl[(1RS,4RS,5RS,6SR)-C5,6,C-η-(5,6,7,8-tetramethylidene-2-bicyclo[2.2.2]octanone)]iron

The preparation and the CD spectra of optically pure (+)-trans-μ-[(1R,4S,5S,6R,7R,8S)-C,5,6,C -η : C,7,8,C-η-(5,6,7,8-tetramethylidene-2-bicyclo [2.2.2]octanone)]bis(tricarbonyliron) ((+)- 7 ) and (+)-tricarbonyl[(1S,4S,5S,6R)-C-5,6,C-η-(5,6,7,8,-tetramethylidene-2-bicyclo[2.2.2]octanone)]iron ((+)- 8 ), and of its 3-deuterated derivatives (+)-trans-μ-[(1R,3R,4S,5S,6R,7R,8S)-C,5,6,C-η : C,7,8,C-η-5,6,7,8-tetramethylidene(3-D)-2-bicyclo[2.2.2]-(octanone)]bis(tricarbonyliron) ((+)- 11 ) and (+)-tricarbonyl[(1S,3R,4S,5S,6R)-C-5,6,C- η-(5,6,7,8-tetramethylidene(3-D)-2-bicyclo[2.2.2]octanone)]iron ((+)- 12 ) are reported. The chirality in (+)- 7 and (+)- 8 is due to the Fe(CO)₃ moieties uniquely. The signs of the Cotton effects observed for (+)- 7 and (+)- 8 obey the octant rule (ketone n→π*_CO transition). Optically pure (?)-3R-5,6,7,8-tetramethylidene(3-D)-2-bicyclo[2.2.2]octanone ((?)- 10 ) was prepared. Its CD spectrum showed an ‘anti-octant’ behaviour for the ketone n→π*_CO transition of the deuterium substituent. The CD spectra of the alcoholic derivatives (?)-trans-μ-[(1R,2R,4S, 5S,6R,7R,8S)-C,5,6,C-η : C,7,8,C- η-(5,6,7,8-tetramethylidene-2-bicyclo[2.2.2]octanol)]bis(tricarbonyliron) ((?)- 2 ) and (?)-tricarbonyl- [(1S,2R,4S,5S,6R)- C,5,6,C- η-(5,6,7,8-tetramethylidene-2-bicyclo[2.2.2]octanol)]iron ((?)- 3 ) and of the 3-denterated derivatives (?)- 5 and (?)- 6 are also reported. The CD spectra of the complexes (?)- 2 , (?)- 3 , (+)- 7 , and (+)- 8 were solvent and temperature dependent. The ‘endo’-configuration of the Fe(CO)₃ moiety in (±)- 8 was established by single-crystal X-ray diffraction.     

Synthese von optisch aktiven,natürlichen Carotinoiden und strukturell verwandten Naturprodukten. V. Synthese von (3R, 3′R)-, (3S, 3′S)- und (3R,3′S; meso)-Zeaxanthin durch asymmetrische Hydroborierung. Ein neuer Zugang zu Optisch aktiven Carotinoidbausteinen. Vorläufige Mitteilung

Synthesis of Optically Active Natural Carotenoids and Structurally Related Compounds. V. Synthesis of (3R, 3′R)-, (3S, 3′S)- and (3R,3′S; meso)-zeaxanthin by Asymmetric Hydroboration. A New Approach to Optically Active Carotenoid Building Units The synthesis of (3R, 3′R)-, (3S, 3′S)- and (3R,3′S; meso)-zeaxanthin ( 1 ), ( 19 ) and ( 21 ) is reported utilizing asymmetric hydroboration as the key reaction. Thus, safranol isopropenylmethylether ( 4 ) is hydroborated with (+)- and (?)-(IPC)₂BH to give the optically pure key intermediates 5 and 7 resp., which are transformed into the above-mentioned C₄₀-compounds.     

Circular Dichroism of Planar,Exocyclic S-cis-Butadienes Remotely Perturbed

Optically pure 5,6-dimethylidenebicyclo[2.2.1]hept-2-yl derivatives have been prepared. The sign of the Cotton effects associated with lowest-energy transition of 2–(dicyanomethylidene)-((?)-(1S,4S)- 15 ), (E)-2-(methoxyimino)-((+)-(1S,4S)- 16 ), (Z)-2-(methoxyimino)-5,6-dimethylidenebicyclo[2.2.1]heptane ((?)(1S,4S)- 17 ), and 2,3,5-trimethylidenebicyclo[2.2.1]heptane ((?)-(1R,4S)- 18 ) is opposite to the chirality constituted by the coupling of the electric transition moments of the two homoconjugated π-chromophores (Kuhn-Kirkwood dipole-coupling mechanism). When the substituents at C(2) are not π-functions, no general rule can be retained for the chiroptical properties of the 5,6-dimethylidenebicyclo[2.2.1]hept-2-yl systems as shown for dimethyl acetal (?)-(1S,4S)- 19 , ethylene acetal (+)-(1R,4R)- 20 , exo and endo methyl ethers (+)-(1R,2S,4R)- 21 and (+)-(1R,2R,4R)- 22 , and for spirol[5,6-dimethylidenebicyclo[2.2.1]heptane-2.2'-oxiranes](?)-(1S,2S,4S)- 23 and (?)-(1S,2S,4S)- 24 .     

Synthese und Bestimmung des Chiralitätssinns von (+)-(R)-1-Azabicylo[3.3.1]nonan-2-on

Synthesis and Determination of the Chirality Sense of (+)-(R)-1-Azabicyclo[3.3.1]nonan-2-one Optically active (+)-(R)-1-azabicyclo[3.3.1]nonan-2-one ((+)- 1 ) of known absolute configuration is synthesized in the following way: Resolution of (±)-piperidin-3-ethanol ((±)- 2 ) by fractional recrystallization of its diastereoisomeric salts with (+)-3-bromocamphor-8-sulfonic acid from EtOH gave a less soluble salt that yielded(+)- 2 . The chirality sense of (+)- 2 was shown to be (R) by chemical correlation with the enantiomers of 3-oxocyclopentaneacetic acid ((±)- 8 ) of known absolute configuration. This correlation was effected by a Beckmann rearrangement of the oxime (R)-9 to the pyridone (S)- 10 followed by a direct reduction with LiAlH₄ to give the enantiomer (?)-(S)- 2 that was characterized as its benzyloxycarbonyl derivative (?)-(S)- 3 . The alcohol (+)-3 was converted via (+)- 4 into the nitrile (+)-5 which gave by hydrogenolysis and hydrolysis the (R)-configurated hydrochloride (+)- 6 which was cyclized to the bicyclic (5R)-lactam (+)- 1 in 67% yield by heating with 2 equiv. of dibutyltin(IV) oxide in toluene. The nonplanar amide function in (+)- 1 with the substituents at the N-atomarranged in a trigonal pyramid causes two rather intense Cotton effects at 242 (Δ?_max = +19.5) and 211 nm(Δ?_max = ?17.9) in the CD spectrum. If the molecules of (+)- 1 do exist mainly in the chair-twistboat conformation, the amide chromophore is pyramidally deformed in a sense defined by the absolute configuration at C(5). Therefore, the CD spectrum of the (5R)-lactam (+)- 1 can be used to test theories describing the chiroptical properties of distorted amides.     

Total synthesis of 2-(β-D-ribofuranosyl)thiazole-4-carboxamide (Tiazofurin) and of precursors of ribo-C-nucleosides

(1R,2S,4R)-2-Cyano-7-oxabicyclo[2.2.1]hept-5-en-2-yl (1S′)-camphanate ( 5 ) was transformed into (?)-methyl 2,5-anhydro-3,4,6-O-tris[(tert-butyl)dimethylsilyl]-D -allonate ( 2 ), (+)-1,3-diphenyl-2-{2′,3′,5′-O-tris[(tert-butyl)dimethylsilyl]-β-D -ribofuranosyl}imidazolidine ( 3 ), and the benzamide 20 of 1-amino-2,5-anhydro-1-deoxy-3,4,6-O-tris-[((tert-butyl)dimethylsily)]-D -allitol. Compound 2 was converted efficiently into optically active tiazofurin ( 1 ).     

Isolierung von (2S, 4S)-(+)-γ-Hydroxynorvalin und (2S, 4R)-(−)-γ-Hydroxynorvalin aus Boletus satanas Lenz

We have isolated from the carpophores of Boletus satanas Lenz (Basidiomycetae) (2S,4S)-(+)-γ-hydroxynorvaline ( 1 ) and (2S,4R)-(?)-γ-hydroxynorvaline ( 2 ). The chirality of each diastereomer has been determined by chemical synthesis starting from optically active precursors and by application of different chiroptical methods. Gaschromatographic separation of the derived diastereomeric N-[(S)-α-methoxypropionyl]-lactones reveals that the optical purity of natural 2 is 88% whereas 1 exists as a partial racemate: (2S,4S): (2R,4R) = 3:2. Muscarine could not be detected in the carpophores of B. satanas, contrary to some literature data but basic substances of unknown structure are present in low concentration.     

Prostaglandin chemistry—V : Synthesis of new prostaglandin synthons; 4(R)-(+)- and 4(S)-(−)-t-butyldimethylsiloxycyclopent-2-en-1-one

Optically active prostaglandin intermediates, 4(R)-(+)- and 4(S)-(?)-hydroxycyclopent-2-en-1-one derivatives, were synthesized from 3(R),5(R)-diacetoxycyclopent-1-ene, 3(R)-acetoxy-5(R)-hydroxycyclopent-1-ene and 3(S),5(S)-dihydroxycyclopent-1-ene obtained by microbiological hydrolysis of 3,5-diacetoxycyclopent-1-ene. The absolute configurations of all these compounds were determined by the exciton chirality method and the induced CD method. The optical purities were determined by NMR measurements of the diastereomeric esters of a versatile optically pure acid, (+)-α-methoxy-α-trifluoromethylphenylacetic acid.     

Asymmetric radical cyclization of (2S,3S)-2,3-butanediyl, (2S,4S)-2,4-pentanediyl,and (2S,5S)-2,5-hexanediyl bis(4-vinylbenzoate)s as a model reaction for asymmetric cyclocopolymerization

The asymmetric cyclocopolymerization of bis(4-vinylbezoate) of a chiral diol with styrene is a promising method for the preparation of optically active polystyrene derivatives because of main-chain chirality. However, the mechanism for chirality induction from the chiral diol to the main chain is still unknown. To clarify the chirality induction mechanism, we carried out the radical cyclizations of (2S,3S)-2,3-butanediyl bis(4-vinylbenzoate), (2S,4S)-2,4-pentanediyl bis(4-vinylbenzoate), and (2S,5S)-2,5-hexanediyl bis(4-vinylbenzoate) with tri-n-butyltin hydride or allyltri-n-butyltin as a chain-transfer reagent as model reactions for asymmetric cyclocopolymerization. The absolute configuration was determined with single-crystal X-ray crystallography and a circular dichroism exciton chirality method. The distribution of the stereoisomer showed (R)-configuration selectivity (21–34% diastereomeric excess) in the intramolecular cyclization and an extremely low extent (<1%) of the (S,S)-cyclized product among the four stereoisomers. Therefore, chirality induction is caused by the selective inhibition of the (S,S)-racemo configuration. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4671–4681, 2004     

Synthese von optisch aktiven,natürlichen Carotinoiden und strukturell verwandten Naturprodukten. IX. Synthese von (3R)-Hydroxyechinenon, (3R, 3′R)- und (3R, 3′S)-Adonixanthin, (3R)-Adonirubin,deren optischen Antipoden und verwandten Verbindungen

Synthesis of Optically Active Natural Carotenoids and Structurally Related Compounds. IX. Synthesis of (3R)-Hydroxyechinenone, (3R, 3′R)- and (3R, 3′S)-Adonixanthin, (3R)-Adonirubin, Their Optical Antipodes and Related Compounds The synthesis of racemic and optically active hydroxyechinenone ( 12–14 ), adonixanthin ( 16–19 ), adonirubin ( 22–24 ), meso-astaxanthin ( 26 ) and their corresponding diosphenols 15, 20, 21, 25, 27, 28 , and 29 ) by Wittig reaction is reported, starting from suitable C₁₅-phosphonium salts and C₁₀-aldehydes.     

C45 und C50-Carotinoide. 6. Mitteilung. Synthese eines optisch aktiven cyclischen C20-Bausteins und von Decaprenoxanthin (= (2R, 6R, 2′R, 6′R)-2,2′-Bis(4-hydroxy-3-methylbut-2-enyl)-ϵ, ϵ-carotin)

C₄₅- and C₅₀-Carotenoids: Synthesis of an Optically Active Cyclic C₂₀-Building Block and of Decaprenoxanthin ( = (2R, 6R, 2′R, 6′R)-2,2′-Bis(4-hydroxy-3-methylbut-2-enyl)-?, ?-carotene) The synthesis of the optically active cyclic C₂₀-building block (R, R) -15 and of the optically active C₅₀-carotenoid (2R, 6R, 2′R, 6′R)-decaprenoxanthin ( 1 ) starting from (-)-β-pinene ((S)- 2 ) is reported.     

Synthese und Chiralität von (5R, 6R)-5,6-Dihydro-β, ψ-carotin-5,6-diol, (5R, 6R, 6′R)-5,6-Dihydro-β, ε-carotin-5,6-diol, (5S, 6R)-5,6-Epoxy-5,6-dihydro-β, ψ-carotin und (5S, 6R, 6′R)-5,6-Epoxy-5,6-dihydro-β,ε-carotin

Synthesis and Chirality of (5R, 6R)-5,6-Dihydro-β, ψ-carotene-5,6-diol, (5R, 6R, 6′R)-5,6-Dihydro-β, ε-carotene-5,6-diol, (5S, 6R)-5,6-Epoxy-5,6-dihydro-β,ψ-carotene and (5S, 6R, 6′R)-5,6-Epoxy-5,6-dihydro-β,ε-carotene Wittig-condensation of optically active azafrinal ( 1 ) with the phosphoranes 3 and 6 derived from all-(E)-ψ-ionol ( 2 ) and (+)-(R)-α-ionol ( 5 ) leads to the crystalline and optically active carotenoid diols 4 and 7 , respectively. The latter behave much more like carotene hydrocarbons despite the presence of two hydroxylfunctions. Conversion to the optically active epoxides 8 and 9 , respectively, is smoothly achieved by reaction with the sulfurane reagent of Martin [3]. These syntheses establish the absolute configurations of the title compounds since that of azafrin is known [2].     

Photochemische Umsetzung von optisch aktiven 2-(1′-Methylallyl)anilinen mit Methanol

Photochemical Reaction of Optically Active 2-(1′-Methylallyl)anilines with Methanol It is shown that (?)-(S)-2-(1′-methylallyl)aniline ((?)-(S)- 4 ) on irradiation in methanol yields (?)-(2S, 3R)-2, 3-dimethylindoline ((?)-trans- 8 ), (?)-(1′R, 2′R)-2-(2′-methoxy-1′-methylpropyl)aniline ((?)-erythro- 9 ) as well as racemic (1′RS, 2′SR)-2-(2′-methoxy-1′-methylpropyl) aniline ((±)-threo- 9 ) in 27.1, 36.4 and 15.7% yield, respectively (see Scheme 3). By deamination and chemical correlation with (+)-(2R, 3R)-3-phenyl-2-butanol ((+)-erythro- 13 ; see Scheme 4) it was found that (?)-erythro- 9 has the same absolute configuration and optical purity as the starting material (?)-(S)- 4 . Comparable results are obtained when (?)-(S)-N-methyl-2-(1′-methylallyl)aniline ((?)-(S)- 7 ) is irradiated in methanol, i.e. the optically active indoline (+)-trans- 10 and the methanol addition product (?)-erythro- 11 along with its racemic threo-isomer are formed (cf. Scheme 3). These findings demonstrate that the methanol addition products arise from stereospecific, methanol-induced ring opening of intermediate, chiral trans, -(→(?)-erythro-compounds) and achiral cis-spiro [2.5]octa-4,6-dien-8-imines (→(±)-threo-compounds; see Schemes 1 and 2).     

C45- und C50-Carotinoide. 5. Mitteilung

C₄₅- and C₅₀-Carotenoids. Synthesis of an Optically Active Cyclic C₂₀-Building Block and of (2R,2′S)-3′,4′-Didehydro-1′,2′-dihydro-2-(4-hydroxy-3-methylbut-2-enyl)-2′-(3-methylbut-2-enyl)-β,ψ-caroten-1′-ol (= C. p. 473) The synthesis of the optically active C₂₀-building block (R)- 16 and of the optically active C₅₀-carotenoid C.p. 473 ( 1 ) starting from (?)-β-pinene is reported.     

Optisch aktive 4,5-Epoxy-4,5-dihydro-α-ionone und Synthese der stereoisomeren 4,5:4′,5′-Diepoxy-4,5,4′,5′-tetrahydro-ϵ,ϵ-carotine und der sterische Verlauf ihrer Hydrolyse

Optically Active 4,5-Epoxy-4,5-dihydro-α-ionones; Synthesis of the Stereoisomeric 4,5:4′,5′-Diepoxy-4,5,4′,5′-tetrahydro-?,?-carotenes and the Steric Course of their Hydrolysis We prove that epoxidation with peracid of α-ionone, contrary to a recently published statement, predominantly leads to the cis-epoxide. Acid hydrolysis affords a single 4,5-glycol whose structure, established by an X-ray analysis, shows that oxirane opening occurred with inversion at the least substituted position (C(4)). Stable cis-and trans-epoxides are prepared by epoxidation of the C₁₅-phosphonates derived from α-ionone. Both the racemic and optically active form are used for the synthesis of the 4,5:4′,5′-diepoxy-4,5,4′,5′-tetrahydro-?,?-carotenes having the following configuration in the end groups: meso-cis/cis, meso-trans/trans, rac-cis/trans, rac- and (6R, 6′ R)-cis/cis, rac- and (6R, 6′R)-trans/trans, rac- and (6R, 6′R)-cis/trans, and (6R, 6′ R)-cis/?. Acid hydrolysis of the cis/cis-epoxycarotenoids under relatively strong conditions occurs again with inversion at C(4)/C(4′) in case of the cis/cis-epoxycarotenoids, but at C(5)/C(5′) in case of the trans/trans-epoxycarotenoids. An independent synthesis of this 4,5,4′,5′-tetrahydro-?,?-carotene-4,5,4′,5′-tetrol is presented. The irregular results of the oxirane hydrolysis are explained by assumption of neighbouring effects of the lateral chain. 400-Mz-¹H-NMR data are given for each of the stereoisomeric sets. In the visible range of the CD spectra, the (6R, 6R′)-epoxycarotenoids compared with (6R, 6R′)-?,?-carotene exhibit an inversion of the Cotton effects.     

Mammalian Alkaloids: Configurations of Optically Active Salsoline- and 3′,4′-Dideoxynorlaudanosoline-1-carboxylic Acids

Synthesis of the optical isomers of (±)-methyl 6,7-dimethyl-3′,4′-dideoxynorlaudanosoline-1-carboxylate ((±)- 2 ) was accomplished by reaction of (±)- 2 with (+)-(R)-1-phenylethyl isocyanate, separation of the urea diastereoisomers (?)- 4A and (+)- 4B , and alcoholysis of the ureas in refluxing BuOH. Optically active isoquinoline-carboxylates 2A , B and hydantoins 8A , B isolated were characterized. The absolute configuration of the reaction products was established by X-ray analysis of the optically active hydantoin (+)- 8A . Hydrolysis of the methyl isoquinolinecarboxylates 2A , B with 48% HBr soln. at reflux afforded the desired optically active 3′,4′-dideoxynorlaudanosoline-1-carboxylic acids 1A , B required for enzyme-inhibition studies. Details of the X-ray diffraction analysis of (+)-methyl salsoline-1-carboxylate hydrobromide ((+)- 11A ·HBr) prepared earlier are included. CD spectra of (+)-(S)-methyl 6,7-dimethyl-3′,4′-dideoxynorlaudanosoline-1-carboxylate hydrobromide ((+)- 2A . HBr) and (?)-(R)-methyl salsoline-1-carboxylate hydrochloride ((?)- 11B ·HCl) confirmed the assignment of their (S)- and (R)-configurations, respectively.     

C45- und C50-Carotinoide. 4. Mitteilung. Synthese von optisch aktiven cyclischen C20-Bausteinen und von (2R,2′R)-2,2′-Bis(4-hydroxy-3-methyl-2-butenyl)-β,β-carotin ( = C.p. 450)

C₄₅- and C₅₀-Carotenoids: Synthesis of Optically Active Cyclic C₂₀-Building Blocks and of (2R,2′R)-2,2′-Bis(4-hydroxy-3-methyl-2-butenyl)-β,β-carotene ( = C.p. 450) The synthesis of the optically active C₂₀-building blocks (R)- 26 and (R)- 39 and of the optically active cyclic C₅₀-carotenoid C.p. 450 ( 3 ) starting from (?)-β-pinene is reported.     

The Circular Dichroism of 5,6-Dimethylidene-2-bicyclo[2.2.n]alky Esters. Chiral Exciton Coupling between Benzoate and Exocyclic s-cis-Butadiene Chromophores

The optically pure aryl-substituted 5,6-dimethylidene-2-bicyclo[2.2.1]heptyl benzoates 12–21 were prepared; their UV absorption and CD spectra are reported. The (?)-(1S,2S)-esters 17–21 with carbonyl groups in endo-position exhibit typical excitonsplit Cotton effects whereas the corresponding (?)-(1S,2R)-esters 12 - 16 with carbonyl groups in exo-position do not present such effects. The chiral exciton coupling between the exocyclic diene and a remote p-substituted benzoate chromophore can be used for unambiguous assignment of the absolute configuration of 5,6-dimethylidene-2-endo-bicyclo[2.2.1]heptyl derivatives. The method is applied to establish the absolute configuration of 5,6-dimethylidene-2-exo and -2-endo-bicyclo[2.2.2.]octyl p-bromobenzoates (?)- 24 and (?)- 25 .     

Synthesen von (1R)-cis-3-(2′,2′-Dihalovinyl)-2, 2-dimethylcyclopropan-carbonsäuren via Favorskii-Umlagerung von optisch aktiven Cyclobutanonen

Syntheses of (1R)-cis-3-(2′,2′-Dihalovinyl)-2,2-dimethylcyclopropane Carboxylic Acids via Favorskii-rearrangement of Optically Active Cyclobutanones The cis-cyclobutanones 7 are resolved by means of optically active amine salts of their sodium hydrogen sulfite adducts. The desired (1R)-cis-carboxylic acids 9 are obtained from the (+)-cis-cyclobutanones 7 via Favorskii-rearrangement and HX-elimination. The recycling of undesired (?)-cis-cyclobutanones 7 is carried out in good yield by their racemization, thus rendering the total synthesis 1 + 2 → 9 chirally economic.     

Über die Stereoselektivität der α-Alkylierung von (1R, 2S) (+)-cis-2-hydroxy-cyclohexancarbonsäureäthylester

The Stereoselectivity of the α-Alkylation of (+)-(1R, 2S)-cis-Ethyl-2-hydroxy-cyclohexanecarboxylate In continuation of our work on the stereoselectivity of the α-alkylation of β-hydroxyesters [1] [2], we studied this reaction with the title compound (+)- 2 . The latter was prepared through reduction of 1 with baker's yeast. Alkylation of the dianion of (+)- 2 furnished (?)- 4 in 72% chemical yield (Scheme 1) and with a stereoselectivity of 95%. Analogously, (?)- 7 was prepared with similar yields. Oxidation of (?)- 4 and (?)- 7 respectively furnished the ketones (?)- 6 (Scheme 3) and (?)- 8 (Scheme 4) respectively, each with about 76% enantiomeric excess (NMR.). It is noteworthy that yeast reduction of rac- 6 (Scheme 3) is completely enantioselective with respect to substrate and product and gives optically pure (?)- 4 in 10% yield, which was converted into optically pure (?)- 6 (Scheme 3). The alkylation of the dianionic intermediate shows a higher stereoselectivity (95%) from the pseudoequatorial side than that of 1-acetyl- or 1-cyano-4-t-butyl-cyclohexane (71% and 85%) [9] or that of ethyl 2-methyl-cyclohexanecarboxylate (82%). The stereochemical outcome of the above alkylation is comparable with that found in open chain examples [1] [2]. Finally (+)-(1R, 2S)- 2 was also alkylated with Wichterle's reagent to give (?)-(1S, 2S)- 9 in 64% yield. The latter was transformed into (?)-(S)- 10 and further into (?)-(S)- 11 (Scheme 5). (?)-(S)- 10 and (?)-(S)- 11 showed an e.e. of 76–78% (see also [11]). Comparison of these results with those in [11] confirmed our former stereochemical assignment concerning the alkylation step.     

Optically active imidazole-containing polymers

In order to investigate the stereospecificity of enzyme-catalyzed reactions, an optically active copolymer of 4(5)-vinylimidazole and 2,5(S)-dimethyl-1-hepten-3-one was synthesized, and its effects on the solvolytic rates, in ethanol-water, of the p-nitrophenyl and 4-carboxy-2-nitrophenyl esters of 3(R)- and 3(S)-methylpentanoic acid and of the commercially available N-carbobenzoxy-(R)- and (S)-phenylalanine p-nitrophenyl esters were investigated. The optically active comonomer was prepared by thermal decomposition of solid (+)-1-piperidino-2,5(S)-dimethylheptan-3-one hydrochloride, which was obtained from the reaction of 2(S)-methylbutyllithium with 3-piperidino-2-methylpropionitrile. The 3(R)-methylpentanoic acid was prepared in 92% optical purity from L -alloisoleucine via diazotization in concentrated hydrobromic acid and subsequent reductive debromination with zinc amalgam in dilute hydrochloric acid. In the optically active copolymer-catalyzed solvolyses of the optically active esters performed at pH values of 6–8 no significant differences between the solvolytic rates of (R) and (S) isomers of substrates were observed. Poly-L -histidine was also employed as a catalyst for the solvolyses of these substrates. At pH 6.0 in ethanol–water the latter catalyst also failed to exhibit specificity towards (R) and (S) substrates.