- Diastereoselective sulfa-Michael reactions controlled by a biomass-derived chiral auxiliary
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A family of chiral auxiliaries derived from the lignocellulosic biomass pyrolysis product levoglucosenone (LGO) has been screened in the sulfa-Michael reaction. When promoted by inorganic bases with potassium counterions, the auxiliary with geminal benzyl substituents showed diastereoselectivity up to 90:10 for a broad range of α,β-unsaturated esters.
- Klepp, Julian,Podversnik, Harald,Puschnig, Johannes,Wallace, Andrew,Greatrex, Ben W.
-
supporting information
p. 3894 - 3903
(2019/06/18)
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- Diastereoselective photocycloaddition reactions of 2-naphthalenecarboxylates and 2,3-naphthalenedicarboxylates with furans governed by chiral auxiliaries and hydrogen bonding interactions
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By using chiral auxiliaries and hydrogen bonding interactions, we have developed diastereoselective photocycloaddition of 2-naphthalenecarboxylates and 2,3-naphthalenedicarboxylates with furan derivatives. In photoreactions of (?)-menthyl 2-naphthalenecarboxylate with furan and 3-furanmethanol, respective maximum 48% and 40% diastereomeric excesses (d.e.) are observed. In photoreactions of di-8-phenyl-(?)-menthyl 2,3-naphthalenedicarboxylate with 3-furanmethanol, maximum 67% d.e. is obtained. Use of solvents of low polarity, low temperatures and low furan concentration leads to increased diastereoselectivities. Variable-temperature (VT) NMR and fluorescence quenching studies indicate that hydrogen bonding interactions between the carbonyl oxygen of naphthalenecarboxylic acid esters and the OH group in 3-furanmethanol take place in both the ground and excited states. The results of computational studies show that geometries of C2 symmetric naphthalenedicarboxylate reactants are important in governing the high diastereoselectivity in the photoreactions of 2,3-naphthalenedicarboxylates.
- Maeda, Hajime,Koshio, Norihiro,Tachibana, Yuko,Chiyonobu, Kazuhiko,Konishi, Gen-ichi,Mizuno, Kazuhiko
-
-
- Method for Highly Enantioselective Ligation of Two Chiral C(sp3) Stereocenters
-
A method is described for the joining of two α-lithiated C(sp3) stereocenters efficiently and with retention of configuration. The key step involves the effective removal of two electrons from a chiral organocuprate R2CuLi, by i-propyl 2,4-dinitrobenzoate to form a Cu(III) complex that undergoes at -90 °C accelerated reductive elimination enantioselectively and exclusively without the formation of free radicals.
- Bhimireddy, Eswar,Corey
-
supporting information
p. 11044 - 11047
(2017/08/22)
-
- Diastereoselective anodic hetero- and homo-coupling of menthol-, 8-methylmenthol- and 8-phenylmenthol-2-alkylmalonates
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Diastereoselective radical coupling was achieved with chiral auxiliaries. The radicals were generated by anodic decarboxylation of five malonic acid derivatives. These were prepared from benzyl malonates and four menthol auxiliaries. Coelectrolyses with 3,3-dimethylbutanoic acid in methanol at platinum electrodes in an undivided cell afforded hetero-coupling products in 22-69% yield with a diastereoselectivity ranging from 5 to 65% de. Electrolyses without a coacid led to diastereomeric homo-coupling products in 21-50% yield with ratios of diastereomers being 1.17:2.00:0.81 to 7.03:2.00. The stereochemistry of the new stereogenic centers was confirmed by X-ray structure analysis and 13C NMR data.
- Letzel, Matthias C.,Sch?fer, Hans J.,Fr?hlich, Roland
-
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- Synthesis of the Privileged 8-Arylmenthol Class by Radical Arylation of Isopulegol
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Hydrogen atom transfer (HAT) circumvents a disfavored Friedel-Crafts reaction in the derivatization of the inexpensive monoterpene isopulegol. A variety of readily prepared aryl and heteroaryl sulfonates undergo a formal hydroarylation to form 8-arylmenthols, privileged scaffolds for asymmetric synthesis, as typified by 8-phenylmenthol. High stereoselectivity is observed in related systems. This use of HAT significantly extends the chiral pool from the inexpensive monoterpene isopulegol.
- Crossley, Steven W. M.,Martinez, Ruben M.,Guevara-Zuluaga, Sebastián,Shenvi, Ryan A.
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p. 2620 - 2623
(2016/06/15)
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- Diastereoselective Radical Hydroacylation of Alkylidenemalonates with Aliphatic Aldehydes Initiated by Photolysis of Hypervalent Iodine(III) Reagents
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Diastereoselective radical hydroacylation of chiral alkylidenemalonates with aliphatic aldehydes is realized by the combination of a hypervalent iodine(III) reagent and UV-light irradiation. The reaction is initiated by the photolysis of hypervalent iodine(III) reagents under mild, metal-free conditions, and is the first example of diastereoselective addition of acyl radicals to olefins to afford chiral ketones in a highly stereoselective fashion. The obtained optically active ketones are useful chiral synthons, as exemplified by the short formal synthesis of (-)-methyleneolactocin.
- Selvakumar, Sermadurai,Sakamoto, Ryu,Maruoka, Keiji
-
supporting information
p. 6552 - 6555
(2016/05/09)
-
- Asymmetric 1,2-Perfluoroalkyl Migration: Easy Access to Enantioenriched α-Hydroxy-α-perfluoroalkyl Esters
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This study has led to the development of a novel, highly efficient, 1,2-perfluoro-alkyl/-aryl migration process in reactions of hydrate of 1-perfluoro-alkyl/-aryl-1,2-diketones with alcohols, which are promoted by a Zn(II)/bisoxazoline and form α-perfluoro-alkyl/-aryl-substituted α-hydroxy esters. With (-)-8-phenylmenthol as the alcohol, the corresponding menthol esters are generated in high yields with excellent levels of diastereoselectivity. The mechanistic studies show that the benzilic ester-type rearrangement reaction takes place via an unusual 1,2-migration of electron-deficient trifluoromethyl group rather than the phenyl group. The overall process serves as a novel, efficient, and simple approach for the synthesis of highly enantioenriched, biologically relevant α-hydroxy-α-perfluoroalkyl carboxylic acid derivatives.
- Wang, Pan,Feng, Liang-Wen,Wang, Lijia,Li, Jun-Fang,Liao, Saihu,Tang, Yong
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p. 4626 - 4629
(2015/04/27)
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- C-selective and diastereoselective alkyl addition to β,γ-alkynyl-α-imino esters with zinc(II)ate complexes
-
Since umpolung α-imino esters contain three electrophilic centers, regioselective alkyl addition with traditional organometallic reagents has been a serious problem in the practical synthesis of versatile chiral α-amino acid derivatives. An unusual C-alkyl addition to α-imino esters using a Grignard reagent (RMgX)-derived zinc(II)ate was developed. Zinc(II)ate complexes consist of a Lewis acidic [MgX]+moiety, a nucleophilic [R3Zn]- moiety, and 2[MgX2]. Therefore, the ionically separated [R3Zn]- selectively attacks the imino carbon atom, which is most strongly activated by chelation of [MgX]+. In particular, chiral β,γ-alkynyl-α-imino esters can strongly promote highly regio- and diastereoselective C-alkylation because of structural considerations, and the corresponding optically active α-quaternary amino acid derivatives are obtained within 5 minutes in high to excellent yields.
- Hatano, Manabu,Yamashita, Kenji,Mizuno, Mai,Ito, Orie,Ishihara, Kazuaki
-
supporting information
p. 2707 - 2711
(2015/03/04)
-
- Stereoselective synthesis of trans-THF rings using an oxidative cyclisation-radical deoxygenation sequence: Application to the formal synthesis of trans-(2R,5R)-linalool oxide
-
An efficient stereoselective synthesis of cis-2,5-disubtituted tetrahydrofuran (THF) diols has been achieved using permanganate-mediated oxidative cyclisation of 1,5-diene precursors. The facial selectivity during the course of cyclisation was induced by incorporating conveniently accessible chiral auxiliaries such as (2R)-10,2-camphorsultam, (S)-4-benzyloxazolidin-2-one and (-)-8-phenylmenthol. The use of (2R)-10,2-camphorsultam furnished the desired THF product as a single isolated diastereoisomer. Conformational analyses are presented to rationalize the origin of facial selectivity and synthetic investigation towards successfully accomplished transformation of cis-2,5-disubstituted THF diols into corresponding trans-THF compounds is also described, leading to a stereoselective formal synthesis of trans-(2R,5R)-linalool oxide.
- Sheikh, Nadeem S.
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p. 3941 - 3953
(2015/02/19)
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- Highly stereoselective cycloadditions of Danishefsky's diene to (-)-8-phenylmenthyl and (+)-8-phenylneomenthyl glyoxylate N-phenylethylimines
-
Enantiopure 4-oxo-pipecolic acid derivatives were obtained by double asymmetric induction aza-Diels-Alder reactions between chiral glyoxylate N-phenylethylimines and Danishefsky's diene mediated by zinc iodide. The key to success was the use of iminoacetates possessing two chiral auxiliaries, N-(S)- or N-(R)-1-phenylethyl and (-)-8-phenylmenthyl or (+)-8-phenylneomenthyl. Adducts were formed in good yields (78-81%), with complete regioselectivity and high diastereoselectivity (87-96%). The absolute configuration of the adducts formed was unequivocally assigned through NMR, specific optical rotation and X-ray data of appropriated derivatives. These cycloadducts can serve as precursors for bioactive piperidinic azasugars and pipecolic acid derivatives.
- García-Mera, Xerardo,Alves, Maria J.,Goth, Albertino,Do Vale, Maria Luísa,Rodríguez-Borges, José E.
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p. 2909 - 2919
(2013/04/10)
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- Lewis acid mediated asymmetric Diels-Alder reactions of chiral 2-phosphonoacrylates
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2-Phosphonoacrylates containing four chiral alcohol auxiliaries were efficiently prepared and evaluated in Lewis acid mediated Diels-Alder reactions. Under the activation of SnCl4, all reactions performed in CH 2Cl2 at -65 °C exclusively afforded the endo (endo-to-carboxylate) cycloadducts with dr's ranging from 50:50 to >99:1. The best facial selectivity was obtained from the substrate bearing a (-)-phenylmenthyl group, to give adducts as (dr >99:1) or almost as (dr = 99:1) single diastereomers. Detailed strategies for the structural elucidation of the cycloadducts as well as a rationalization of the observed stereoselectivity are described.
- Zhu, Jia-Liang,Chen, Po-Erh,Huang, Hue-Wen
-
-
- Double asymmetric induction as a mechanistic probe: The doubly diastereoselective conjugate addition of enantiopure lithium amides to enantiopure α,β-unsaturated esters and enantiopure α,β-unsaturated hydroxamates
-
The doubly diastereoselective conjugate addition of the antipodes of lithium N-benzyl-N-(α-methylbenzyl)amide to a range of enantiopure α,β-unsaturated esters [derived from Corey's 8-phenylmenthol chiral auxiliary] and enantiopure α,β-unsaturated hydroxamates [derived from our 'chiral Weinreb amide' auxiliary (S)-N-1-(1′-naphthyl)ethyl-O-tert- butylhydroxylamine] has been used as a mechanistic probe to determine the reactive conformations of these acceptors.
- Davies, Stephen G.,Lee, James A.,Roberts, Paul M.,Thomson, James E.,Yin, Jingda
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p. 6382 - 6403
(2011/09/19)
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- Stereoselective synthesis of polyhydroxylated pyrrolidines: a route to novel 3,5-bis(hydroxymethyl)pyrrolidines from 2-azabicyclo[2.2.1]hept-5-enes
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An efficient preparation of racemic and chiral 2-functionalized-3,5-bis(hydroxymethyl)pyrrolidines is described. The method uses 2-azabicyclo[2.2.1]hept-5-enes, readily obtained from glyoxylates of aliphatic amines and cyclopentadiene, as starting material. The hydroxylation of the double bond followed by the oxidative cleavage of the six-membered ring and in situ reduction of the dialdehyde intermediate gives the title pyrrolidines.
- Alves, M. José,García-Mera, Xerardo,Vale, M. Luisa C.,Santos, Teresa P.,Aguiar, Fábio R.,Rodríguez-Borges, José E.
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p. 7595 - 7597
(2007/10/03)
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- Enantioconvergent synthesis by sequential asymmetric Horner-Wadsworth-Emmons and palladium-catalyzed allylic substitution reactions
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A new method for enantioconvergent synthesis has been developed. The strategy relies on the combination of an asymmetric Horner-Wadsworth-Emmons (HWE) reaction and a palladium-catalyzed allylic substitution. Different α-oxygen-substituted, racemic aldehydes were initially transformed by asymmetric HWE reactions into mixtures of two major α,β-unsaturated esters, possessing opposite configurations at their allylic stereocenters as well as opposite alkene geometry. Subsequently, these isomeric mixtures of alkenes could be subjected to palladium-catalyzed allylic substitution reactions with carbon, nitrogen, and oxygen nucleophiles. In this latter step, the respective (E) and (Z) alkene substrate isomers were observed to react with opposite stereospecificity: the (E) alkene reacted with retention and the (Z) alkene with inversion of stereochemistry with respect to both the allylic stereocenter and the alkene geometry. Thus, a single γ-substituted ester was obtained as the overall product, in high isomeric purity. The method was applied to a synthesis of a subunit of the iejimalides, a group of cytotoxic macrolides.
- Pedersen,Hansen,Kane,Rein,Helquist,Norrby,Tanner
-
p. 9738 - 9742
(2007/10/03)
-
- Chiral auxiliaries for asymmetric radical cyclization reactions: application to the enantioselective synthesis of (+)-triptocallol.
-
[figure: see text] A series of epimeric 8-aryl menthyl derivatives 5a-d and 6a-l, prepared from the same chiral source (R)-pulegone, were employed as chiral auxiliaries in the asymmetric radical cyclization reactions of beta-keto esters mediated by Mn(OAc)3. Chiral precursors 8c and 8d provided the cyclization products 10c and 10d, respectively, as single isomers (dr > 99:1), whereas the cyclization of precursor 9k gave 13k with good stereoselectivity (dr = 24:1). Diastereomer 13e was employed as the key intermediate in the enantioselective synthesis of (+)-triptocallol in 90% ee.
- Yang,Xu,Bian
-
p. 111 - 114
(2007/10/03)
-
- Engineering Acyclic Stereocontrol in the Alkylation of Vinylglycine-Derived Dianions: Asymmetric Synthesis of Higher α-Vinyl Amino Acids
-
A generalizable synthesis of higher L-α-vinyl amino acids is presented. The strategy pursued here involves the introduction of the amino acid side chain via the alkylation of a chiral, vinylglycine-derived dianionic dienolate, bearing the (-)-8-(β-naphthyl)menthyl (d'Angelo) auxiliary. A model is presented that postulates a favored "exo-entended" conformation for this dienolate, leading to Cα-alkylation at the si face. The model invokes internal amidate chelation to control ester enolate geometry and soft-soft interactions between the polarizable β-naphthyl ring of the auxiliary and the extended π-system of the dienolate to shield the re face. Heats of formation for four conformers of this dianion were calculated for their semiempirical optimized geometries (PM3). The results support the notion that in these vinylglycine-derived dianionic dienolates, "exo" conformations are considerable lower in energy than their "endo" counterparts, with the "exo-entended" conformation being most favorable. In fact, the d'Angelo auxiliary gives a greater degree of acyclic stereocontrol in this system when compared with the (-)-8-phenylmenthyl (Corey) and trans-2-(β-naphthyl)-cyclohexyl auxiliaries, using isobutyl iodide and benzyl bromide as model electrophiles. These dianions are generated from the corresponding dehydrobutyrine esters via sequential deprotonation with LDA and n-BuLi (2 equiv). When alkylations are carried out at -78°C in THF-HMPA, they proceed in 65-81% yields, with both regiocontrol (deconjugative α-alkylation is preferred over γ-alkylation) and a great degree of acyclic stereocontrol [91:9 to ≥98:2 diastereomeric ratios (10 examples)]. The auxiliary may be recovered in high yield (generally 90%) using a modification of Gassman's "anhydrous hydroxide" conditions, in which considerably higher temperatures are employed. Among the side chains introduced directly are those of butyrine, leucine, ornithine, phenylalanine, aspartate, valine, and norvaline. The lysine side chain is elaborated via a 4-step sequence from the alkylation product obtained with 1-chloro-4-iodobutane as electrophile. Importantly, to our knowledge, this work represents the first asymmetric synthesis of L-α-vinyl analogues of m-tyrosine, ornithine, and lysine, known time-dependent inhibitors for amino acid decarboxylases.
- Berkowitz, David B.,McFadden, Jill M.,Sloss, Marianne K.
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p. 2907 - 2918
(2007/10/03)
-
- Synthesis and characterization of all stereoisomers of 8-phenylmenthol
-
New, improved and/or specific syntheses of the diastereoisomers of (-)-8-phenylmenthol are described. The configurations of these products, usable as chiral auxiliaries, were confirmed by X-ray diffractometry of their 3,5-dinitrobenzoates.
- Fernandez, Franco,Garcia-Mera, Xerardo,Lopez, Carmen,Rodriguez, Gonzalo,Rodriguez-Borges, Jose Enrique
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p. 4805 - 4815
(2007/10/03)
-
- Enantioselective synthesis of (7R,8R,8aR)- and (7S,8S,8aS)-7-hydroxy-8-indolizidinemethanol by 1,3-dipolar cycloaddition of 1-pyrroline N-oxide to chiral pentenoates
-
The 1,3-dipolar cycloadditions of pyrroline N-oxide (1) with (1R,2S)-trans-2-phenylcyclohexyl- and with (1R,2S,5R)-8-phenylmenthyl-pent-2-enoates (9 and 10) proceed with opposite diastereoselectivities. The two enantiomers of a new dihydroxyindolizidine, (+)-6 and (-)-6, were synthesized using 4 and 5, respectively, as the chiral auxiliary.
- Cordero, Franca Maria,Faggi, Cristina,De Sarlo, Francesco,Brandi, Alberto
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p. 3595 - 3600
(2007/10/03)
-
- Diastereofacial selectivity in ketene [2+2] cycloaddition to endocyclic enecarbamates bearing a chiral auxiliary. Synthesis of the (-)-Geissman-Waiss lactone
-
The diastereofacial selectivity of enecarbamates bearing a chiral auxiliary was evaluated for the [2+2]cycloaddition with dichloroketenes. Diastereofacial selectivity ranged from zero (bornyl and menthyl) to 60% (Greene's auxiliary and 8-phenylmenthyl). Chromatography separation of the diastereomeric azacyclobutanones derived from the 8-phenylmenthyl enecarbamate permitted an enantiodivergent synthesis of the (-)-Geissman-Waiss lactone, a key intermediate in the synthesis of necine bases.
- Miranda, Paulo Cesar M. L.,Correia, Carlos Roque D.
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p. 7735 - 7738
(2007/10/03)
-
- Total synthesis of (-)-epibatidine using an asymmetric Diels-Alder reaction with a chiral n-acylnitroso dienophile
-
An asymmetric total synthesis of (-)-epibatidine (1), isolated from the skin of the Ecuadorian poison frog, Epipedobates tricolor, of the family Dendrobatidae, has been achieved by virtue of the development of asymmetric hereto Diels-Alder (D-A) cycloaddition with an N-acylnitroso dienophile bearing the optically active 8-arylmenthol as a chiral source. Thus, in situ oxidation of the hydroxamic acid ent-12f incorporating the (1S,2R,5S)-8-(2- naphthyl)menthyl auxiliary was performed using the Swern conditions to produce the acylnitroso dienophile, which reacted at once with 2-chloro-5- (1,5-cyclohexadienyl)pyridine (7) to provide the (1S,4R)-meta-aza cycloadduct 24 as a major diastereoisomer. The observed facial diastereoselectivity is consistent with a transition-state model with the naphthyl group in 'stacked' position and with the acylnitroso group in the s-cis conformation, wherein π attractive interaction between the naphthyl and nitrosocarbonyl groups may contribute to facial control. Compound 24 underwent hydrogenation followed by removal of the chiral auxiliary with LiH2NBH3 and reductive cleavage of the N-O bond with Mo(CO)6 to give the amino alcohol derivative 29, which was converted to (-)-epibatidine via bromination followed by cyclization.
- Aoyagi, Sakae,Tanaka, Ryuta,Naruse, Masaichi,Kibayashi, Chihiro
-
p. 8397 - 8406
(2007/10/03)
-
- Chiral auxiliary mediated pictet-spengler reactions: Asymmetric syntheses of (-)-laudanosine, (+)-glaucine and (-)-xylopinine
-
Cyclohexyl-based chiral auxiliaries can be used effectively in an asymmetric Pictet-Spengler synthesis of tetrahydroisoquinoline, aporphine and protoberbine alkaloids. Using this strategy, concise asymmetric syntheses of (-)-laudanosine, (+)-glaucine and (+)- xylopinine have been accomplished.
- Comins, Daniel L.,Thakker, Paresh M.,Baevsky, Matthew F.,Badawi, Mohamed M.
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p. 16327 - 16340
(2007/10/03)
-
- A diastereoselective radical cyclisation approach to pyroglutamates
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The 5-endo radical cyclisation of pyruvic acid derived dehydroalanines which contain chiral ester auxiliaries is reported. Cyclisation of the menthol ester derivative using Bu3SnH at 80°C proceeded with low diastereoselectivity (1.75:1) but the selectivity could be increased to 6:1 on cyclisation of the corresponding 8-phenylmenthyl ester at 20°C.
- Goodall, Karen,Parsons, Andrew F.
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p. 491 - 494
(2007/10/03)
-
- A simple preparation of (R)-(2-cyclopentenyl)acetic acid and (R)-(2-cyclohexenyl)acetic acid using β-diastereoselective radical cyclization in the presence of Lewis acid
-
The alkenyl radical generated from (-)-8-phenylmenthyl 7-iodo-2,6-heptadienoate smoothly cyclized to afford (R)-(2-cyclopentenyl)acetate with 88% de in 90% yield. (R)-(2-Cyclohexenyl)acetate was also obtained with 84% de in 72% yield under the same conditions. The presence of Lewis acid is essential for high diastereoselectivity and chemical yield.
- Nishida,Hayashi,Yamaura,Yanaginuma,Yonemitsu,Nishida,Kawahara
-
p. 269 - 272
(2007/10/02)
-
- Diastereoselectivity in the Preparation of β-Silyl Esters from αβ-Unsaturated Esters and Amides Attachhed to Chiral Auxiliaries
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The conjugate addition of the phenyldimethylsilyl-cuprate reagent to cinnamate and crotonate esters and amides 1 of various known chiral auxiliaries, a-e, is diastereoselective.The sense of diastereoselectivity of silyl-cuprate addition to the esters 1b-d, 8 and 9 is different from established precedent based on carbon-cuprates, but is normal for silyl-cuprate addition to the amide 1a, the imines 1e and 21, and the oxazolidine 6.The chiral auxiliary e gives the best results of those tested, and the silicon-containing group can be removed from the chiral auxiliary using alkoxide ion in aprotic media, making available β-silyl esters 27-29 of high enantiomeric excess, with recovery of the chiral auxiliary 30.
- Fleming, Ian,Kindon, Nicolas D.
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p. 303 - 316
(2007/10/02)
-
- DIASTEREOSELECTIVE REDUCTION OF AN α-KETO-ESTER DERIVED FROM (-)-8-PHENYLMENTHOL: A 4-step synthesis of R-Halostachine analogue
-
An efficient (80percent total yield) 4-step synthesis of 94percent e.e.R-(-)-Halostachine analogue is described.The method offers the possibility to introduce various substituents onto the aromatic ring and various alkyl groups on the amine.A one-step and high yield (ca.100percent) conversion of esters into amides is presented.
- Solladie-Cavallo, Arlette,Bencheqroun, Mohamed
-
p. 1165 - 1171
(2007/10/02)
-
- Asymmetric Synthesis of 2-Alkyl(Aryl)-2,3-dihydro-4-pyridones by Addition of Grignard Reagents to Chiral 1-Acyl-4-methoxypyridinium Salts
-
Grignard addition to a chiral 1-acyl-4-methoxypyridinium salt provides synthetically useful 2-alkyl(aryl)-2,3-dihydro-4-pyridones in high diastereomeric excess.
- Comins, Daniel L.,Goehring, R. Richard,Joseph, Sajan P.,O'Connor, Sean
-
p. 2574 - 2576
(2007/10/02)
-
- PREPARATION OF THREE DIASTEREOISOMERS OF 2-(1-METHYL-1-PHENYLETHYL)-5-METHYLCYCLOHEXAN-1-OL FROM (R)-(+)-PULEGONE
-
New isolation of (1R,2S,5R)-(-)-2-(1-methyl-1-phenylethyl)-5-methylcyclohexan-1-ol ((-)-8-phenylmenthol, Ia), prepared from (R)-(+)-pulegone, is described.The method consists in the preparation of phenylcarbamate of Ia and its transesterification with ethanol.Further two diastereoisomers of (-)-8-phenylmenthol were isolated: the (1S,2R,5R)-isomer IIa and the (1R,2R,5R)-isomer IIIa.Compounds Ia, IIa and IIIa were converted into their respective glyoxylates Ic, IIc and IIIc.
- Cervinka, Otakar,Svatos, Ales,Masojidkova, Milena
-
p. 491 - 498
(2007/10/02)
-
- Synthesis of (2S,3R)-3-Amino-2-hydroxy-5-methylhexanoic Acid: Bridging Effect of KF
-
Natural (2S,3R)-3-amino-2-hydroxy-5-methylhexanoic acid is synthesized in 53-55percent yield (referred to (-)-8-phenylmenthol used as chiral auxiliary) by condensation of 1-nitro-3-methylbutane on (-)-8-phenylmenthol glyoxylate hydrate using KF as a mild base.With a large excess of KF in THF it has been possible to increase the diastereoselectivity of the nitro aldol condensation (up to I/II/III/IV = 77/13/10/0).
- Solladie-Cavallo, A.,Khiar, N.
-
p. 4750 - 4754
(2007/10/02)
-
- Improved Asymmetric Synthesis of 8-Arylmenthols
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A two-step synthesis of a set of arylmenthones 3 from R(+)-pulegone 2 via their silylenoethers 4 is proposed leading in high yields to 8-arylmenthols 1.
- Potin, Dominique,Dumas, Francoise,Maddaluno, Jacques
-
p. 2805 - 2813
(2007/10/02)
-
- Methylenecyclopropanes, XI. - Asymmetric Nickel(0)-Catalyzed Cycloadditions of Methylenecyclopropanes with Chiral Derivatives of Acrylic Acid
-
The nickel(0)-catalyzed codimerisation of methylenecyclopropane 1a or 2,2-dimethylmethylenecyclopropane (1b) with the chiral derivatives of acrylic acid 2a-2f leads to the optically active 3-methylenecyclopentanecarboxylic esters 3a, 3c-3f, 4a, and 4c, or amides 3b and 4b in good yields.The diastereomeric excess accesible depends on the steric demand of the chiral auxiliaries, de values up to 98percent can be achieved.Some improvements of the preparation of optically pure auxiliaries are also described.
- Binger, Paul,Brinkmann, Axel,Roefke, Petra,Schaefer, Bernd
-
p. 739 - 750
(2007/10/02)
-
- THE RACEMIC FORM AND THE TWO ENANTIOMERS OF 4-METHYL-1-NONANOL, A SEX ATTRACTANT OF THE YELLOW MEALWORM, Tenebrio molitor L.
-
The racemic form of 4-methyl-1-nonanol, (R)(S)-1, a sex attractant secreted by the female of the yellow mealworm, has been synthesized in 31 percent overall yield from commercially available methyl 2-octynoate, 2.Almost enantiomerically pure (R)- and (S)-1 have been stereospecifically synthesized in 21.3 and 23.9 percent overall yields, respectively, starting from methyl hydrogen (R)-3-methylglutarate, (R)-3.A precursor for (S)-1, i.e. (S)-3-methyloctanoic acid, (S)-4, has been also prepared in 84 percent yield and over 96 percent enantiomeric purity by the BF3-mediated 1,4-addition of n-pentylcopper to (-)-8-phenylmenthyl crotonate, 15, followed by saponification.The enantiomeric purities of methyl (R)-3-methyloctanoate, (R)-7, and (S)-3-methyl-1-octanol, (S)-8, have been determined by converting these compounds into (R)- and (S)-3-methyloctanoic acid, (R)-4 and (S)-4, respectively, followed by GLC analysis of the corresponding 1-(1-naphthyl)ethylamides obtained from nearly optically pure (R)-1-(1-naphthyl)ethylamine.
- Carpita, Adriano,Magistris, Elisabetta De,Rossi, Renzo
-
-
- Asymmetric Two-Fold Michael Reaction. Synthesis of Optically Active 4-Substituted 1-Decalones from Trimethylsilyl Enol Ether of 1-Acetylcyclohexene
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Acrylates having a chiral auxiliary react with the trimethylsilyl enol ether of 1-acetylcyclohexene in the presence of Et2AlCl to give 4-substituted 1-decalones with 0-70percent diastereoselectivity.The absolute stereostructure of the decalones have been determined by applying the exciton chirality method to the dibenzoate derivative.
- Hagiwara, Hisahiro,Akama, Tsutomu,Okano, Akihiro,Uda, Hisashi
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p. 2149 - 2152
(2007/10/02)
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- STUDIES ON THE REACTION OF α-IMINO ESTERS WITH ORGANOMETALLIC COMPOUNDS
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Benzylzinc reagent reacted with α-amino ester ( 2 ) at the α-carbon exclusively, though other organometallic reagents such as Mg, Al, Cu, Ti, and B derivatives reacted at the nitrogen atom.Use of the (S)-amine as a chiral auxiliary of 2 created the R chirality at the imino carbon.Very high chiral induction was realized in the reaction of prenylzinc reagent with α-imino 8-(-)phenylmenthyl ester ( 10 ).The reaction of 2 with heteroatom substituted allylic organometallic compounds ( 15 ) gave the corresponding α-heteroatom substituted amino acid derivatives ( 16 ).Here again, the allylic zinc reagent gave the adduct in higher yield than the corresponding Ti, Al, and B reagents.
- Yamamoto, Yoshinori,Ito, Wataru
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p. 5415 - 5424
(2007/10/02)
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- Asymmetric -Wittig Rearrangement Involving a Chiral Ester Enolate Terminus. A Chiral Synthesis of erythro-α-Hydroxy-β-alkyl Carboxylic Acid Derivatives
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The title rearrangement of the (E-2-alkenyloxy)acetic esters derived from (-)-8-phenylmenthol has been shown to afford the corresponding 3-alkyl-2-hydroxy-4-pentenoic ester with an extremly high level of diastereoface selection (95-97percent de) along with a high erythro selectivity (90-93percent).
- Takahashi, Osamu,Mikami, Koichi,Nakai, Takeshi
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- Preparation of Pure (-)-(1R,2S,5R)-2-(1-Methyl-1-phenylethyl)-5-methylcyclohexanol in Larger Amounts
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A method is described for the separation of (-)-(1R,2S,5R)-2-(1-methyl-1-phenylethyl)-5-methylcyclohexanol (1; 8-phenylmenthol) in preparative amounts in the form of its chloroacetate 3 from the accompanying diastereomer 2, which is formed according to Corey's synthesis.
- Herzog, Heinz,Scharf, Hans-Dieter
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p. 420 - 421
(2007/10/02)
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- Interactivity of Chiral Catalysts and Chiral Auxiliaries in the Cycloaddition of Activated Dienes with Aldehydes: A Synthesis of L-Glucose
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Eu(fod)3 and Eu(hfc)3 catalyze the cycloaddition of a variety of aldehydes with oxygenated highly substituted butadienes.With achiral dienes, (+)-Eu(hfc)3 shows only modest enantiofacial selectivities.Similarly, modest selectivities were observed in the reactions of several chiral dienes with aldehydes in the presence of the achiral Eu(fod)3.However, the combination of chiral dienes with chiral (+)-Eu(hfc)3 catalyst exhibited striking interactivities, resulting in some instances in diastereofacial excesses of 95 percent.Of the systems examined, only those dienes whose intrinsic facial selectivities are small and opposite in direction to that of the (+)-Eu(hfc)3 catalyst exhibit useful interactivity of the two chiral components.Thus, the diastereomeric excesses observed here do not arise from strictly numerical factoring of componental preferences (simple double diastereoselectivity) but are a consequence of a "specific interactivity", inherent in the process itself.Application of these findings to the synthesis of optically pure substituted pyrans, L-glycolipids, and L-glucose is described.
- Bednarski, Mark,Danishefsky, Samuel
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p. 7060 - 7067
(2007/10/02)
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- ENANTIOSELECTIVE SYNTHESIS OF (+)-CITREOVIRAL USING ASYMMETRIC HYDROXYLATION OF TIGLATE ESTERS
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A microbial metabolite (+)-citreoviral has been synthesized enantio- and stereo-selectively using newly developed asymmetric hydroxylation of tiglate esters for the construction of the key chiral building block.
- Hatakeyama, Susumi,Matsui, Yumiko,Suzuki, Masahiro,Sakurai, Kuniya,Takano, Seiichi
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p. 6485 - 6488
(2007/10/02)
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- Further Synthesis of Optically Active Verrucarinic Acid
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Two new syntheses of verrucarinic acid ((2S,3R)-2,5-dihydroxy-3-methylpentanoic acid) and its derivatives, suitably protected for the further conversion to macrocyclic trichothecenes, are described.The first one makes use of a diastereoselective alkylation of a (-)-(S)-malic acid ester and the regioselective reduction of one carboxyl function to a methyl group.The second approach involves a stereoselective addition of an allylsilane to a chiral glyoxylate.
- Grossen, Peter,Herold, Peter,Mohr, Peter,Tamm, Christoph
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p. 1625 - 1629
(2007/10/02)
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- High Asymmetric Induction in Conjugate Additions of RCu*BF3 to Chiral Enoates
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1,4-Additions of PhCu*BF3, n-BuCu*BF3 and MeCu*BF3 to the trans-8-phenylmenthyl enoates 1 proceeded with high chiral induction.Saponification of the resulting esters 2 gave the corresponding enantiomerically pure β-substituted alkanoic acids 3 and the recovered (-)-8-phenylmenthol in good overall yields.Analogous additions to the cis-crotonate 1 led preferentially to the acids 3 enantiomeric to those obtained from the trans-crotonate 1, although with lower selectivity.A stereochemical model is proposed consistent with the observed results (Scheme 2, Table).
- Opplzer, Wolfgang,Loeher, Heinz J.
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p. 2808 - 2811
(2007/10/02)
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- High Asymmetric Induction in Lewis Acid-Promoted Intramolecular Ene-Type Reactions: A Diastereo- and Enantioselective Synthesis of (+)-α-Alolokainic Acid
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The monocyclic amino diacid (+)-α-allokainic acid 1 has been prepared enantioselectively from the ester of cis-β-chloroacrylic acid and (-)-8-phenylmenthol by a series of four synthetic operations in over 15percent yield.The crucial step is the intramolecular 'ene-type' reaction of the (Z)-diene 4 which on treatment with a mild Lewis acid undergoes a highly accelerated, dia- and enantiostereoselective cyclization to give the pyrrolidines 6 and 7 in a ratio of 95:5 (Scheme 3).Subsequent ester hydrolysis regenerates the auxiliary chiral alcohol.Similar cyclization of the (E)-diene 5 furnished a 15:85 mixture of 6 and 7 showing an efficient reversal of the optical induction by variation of the enoate geometry.
- Oppolzer, Wolfgang,Robbiani, Christian,Baettig, Kurt
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p. 2015 - 2018
(2007/10/02)
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