- Asymmetric Wittig reaction of chiral arsonium ylides - I. Asymmetric olefination of 4-substituted cyclohexanones
-
Asymmetric Wittig-type olefination of 4-substituted cyclohexanones with chiral ligand-modified stable arsonium ylides has been examined. The 8-phenylmenthol-derived chiral arsonium ylide of 4 reacted with prochiral ketones 9a-d at -15°C to give the 4-substituted cyclohexylideneacetates 11a-d in 58-69% yield and in up to 80% diastereomeric excess (de).
- Dai, Wei-Min,Wu, Jinlong,Huang, Xian
-
-
Read Online
- Asymmetric Sommelet-Hauser rearrangement of N-benzylic ammonium salts
-
(Chemical Equation Presented) [2,3] over [1,2]: The asymmetric Sommelet-Hauser rearrangement of an ammonium salt derived from N-benzylic proline-derived or N-benzylic glycine (-)-8-phenylmenthol ester is shown to proceed with remarkably high levels of stereoselectivity. The method provides unique and efficient access to optically active α-aryl amino acid derivatives.
- Tayama, Eiji,Kimura, Hiroshi
-
p. 8869 - 8871
(2008/09/19)
-
- Exceptionally mild, high-yield synthesis of α-fluoro acrylates
-
Novel achiral and chiral alkyl α-(1,3-benzothiazol-2-ylsulfonyl)- α-fluoroacetates can be readily synthesized by metalation-fluorination of (1,3-benzothiazol-2-ylsulfonyl)acetates. DBU-mediated condensations of these fluorinated synthons with aldehydes proceed in a facile manner at 0 °C or at room temperature giving high yields of α-fluoro acrylates. Ketones are unreactive under these conditions. The presence of fluorine renders the synthon substantially more reactive compared to the unfluorinated analogue. Reactivity of α-(1,3-benzothiazol-2-ylsulfonyl)-α-fluoroacetate and the Horner-Wadsworth-Emmons reagent (EtO)2P(O)CHFCOOEt has also been compared.
- Zajc, Barbara,Kake, Shivani
-
p. 4457 - 4460
(2007/10/03)
-
- Asymmetric induction in Darzens condensation by means of (-)-8-phenylmenthyl and (-)-menthyl auxiliaries
-
Asymmetric Darzens condensation of benzaldehyde and various ketones has been investigated. The condensation of acetophenone, propiophenone and symmetric ketones with (-)-8-phenylmenthyl halogenoacetates 3a,b afforded the corresponding glycidic esters cis-12, cis-13 and 15-19 in 77-96% de, respectively, as the major products. Aza-Darzens condensation between N-benzylideneaniline and 3a occurred to give the trans-aziridine 21 as the major isomer in >85% de. The stereochemistry of the major diastereoisomers of cis-12 and 18 was confirmed by their conversion into the known optically active diols 22 and 24. The configuration of the major product of cis-12 was determined to be 2R,3R and that of 18 to be 2R. The geometric and disastereofacial selectivities were understandable in terms of the open-chain or non-chelated antiperiplanar transition state model in the initial aldol-type reaction.
- Takagi, Ryukichi,Kimura, Jyunji,Shinohara, Yoshihiro,Ohba, Yuko,Takezono, Kyoko,Hiraga, Yoshikazu,Kojima, Satoshi,Ohkata, Katsuo
-
p. 689 - 698
(2007/10/03)
-
- Remarkable examples of double diastereodifferentiation: Application to the eudistomin and eudistomidin alkaloids
-
Nucleophilic addition of chiral enolates 1 and ent-1 with chiral iminium ion 2a occur with total stereochemical control.
- Polniaszek, Richard P.,Bell, Stephanie J.
-
p. 575 - 578
(2007/10/02)
-
- Synthesis of an optically pure 3-unsubstituted β-lactam using an asymmetric reformatsky reaction and its conversion to cholesterol absorption inhibitors
-
Asymmetric induction by several chiral alcohols in the reaction of their bromoacetates with imines in the presence of activated Zn (Reformatsky reaction) was studied. Trans-2-phenlcyclohexanol and phenyl menthol gave β- lactam 9, obtained by cyclizing the diastereoisomeric β-aminoesters 8, in > 99%ee. The resulting chiral 3-unsubstituted azetidin-2-one 9 was converted to 3-substituted products 11, 12, and 13 which exhibit cholesterol absorption inhibitory activity.
- Shankar,Kirkup,McCombie,Clader,Ganguly
-
p. 4095 - 4098
(2007/10/03)
-
- High diastereofacial selectivity in the 1,3-dipolar cycloaddition of chiral azomethine ylides
-
Excellent diastereofacial and endo/exo stereoselectivities have been obtained in cycloaddition of the chiral azomethine ylide generated from 4-phenyloxazolidine acetic acid (-)-8-phenylmenthyl ester 1e.
- Deprez,Royer,Husson
-
p. 1189 - 1192
(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)
-
- ENANTIOSELECTIVE SYNTHESIS OF OPTICALLY PURE S-ISOSERINE
-
KF-promoted addition of nitromethane on (-)-8-phenylmethyl glyoxylate monohydrate affords, after one purification, optically pure (-)S isoserine in about 50percent yield.
- Solladie-Cavallo, A.,Khiar, N.
-
p. 2189 - 2192
(2007/10/02)
-
- ASYMMETRIC INDUCTION IN THE ENE REACTION OF GLYOXYLATE ESTERS OF 8-PHENYLMENTHOL
-
We recently communicated (J.K.Whitesell, A.Bhattacharya, D.A.Aguilar and K.Henke, J.Chem.Soc.Chem.Commun. 989 (1982)) a highly efficient and effective method for the control of absolute stereochemistry through asymmetric induction in the ene reaction the chiral glyoxylate 1 with alkenes.We now have accumulated sufficient information on this process in terms of both its mechanistic details as well as its scope and applicability to a variety of situations that warrants a more complete presentation of these reactions.
- Whitesell, James K.,Bhattacharya, Apurba,Buchanan, Charles M.,Chen, H. H.,Deyo, Don,et al.
-
p. 2993 - 3002
(2007/10/02)
-
- Further Synthesis of Optically Active Verrucarinic Acid
-
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
-
p. 1625 - 1629
(2007/10/02)
-