The asymmetric hetero-Diels–Alder reaction and addition of allylic organometallics to 10-N,N-dicyclohexylsulphamoyl-(2R)-isobornyl glyoxylate
摘要:
The recent development of very effective chiral auxiliaries has led to the design of 10-N,N-dicyclohexylsulphamoyl-(R)-isoborneol, which is similar to Oppolzer's (2R)-bornane-10,2-sultam but less effective on account of a less rigid structure. 10-N,N-Dicyclohexylsulphamoyl-(R)-isobornyl glyoxylate was examined in Diels-Alder and organometallic addition reactions. The results obtained were compared with those achieved by application of N-glyoxyloyl-(2R)-bornane-10,2-sultam. (C) 1999 Elsevier Science Ltd. All rights reserved.
The synthesis of oximes and nitroalkanes bearing a chiral auxiliary unit: convenient substrates for the preparation of enantiomerically pure nitrile oxides
We report the synthesis of four new oximes and three nitroalkanes bearing a chiral unit. All these compounds were converted into nitrile oxides and subjected to 1,3-dipolar cycloaddition with 3-E-hexene, giving the corresponding 2-isoxazolines in fair yields but only with moderate stereoselectivities.
Diastereoselectivity in the hetero [4+2] cycloaddition of cyclopentadiene to N-benzyliminoacetyl derivatives of (2R)-bornane-10,2-sultam and other chiral secondary alcohols
Various protonated chiral glyoxyloyl-alpha -imino-N-benzyl hetero-dienophiles have been examined in the diastereoselective exo-cycloaddition to cyclopentadiene at -78 degreesC promoted by CF3CO2-BF3, a dissociated non-nucleophilic counter ion. The best pi -facial selectivities were observed with (2R)-bornane-10,2-sultam (76% d.e.) and (2R)-10-dicyclohexylsulfonamoyl-isoborneol (80% d.e.) as chiral auxiliaries. These conditions were found to be superior in terms of yields and selectivities as compared to analogous aza-dienophiles treated with simple Lewis acids or under thermal conditions. Absolute configurations were assigned on the basis of an X-ray analysis of the major cycloadduct (3 'S)-3a as well as by chiroptical comparison with the corresponding new amino alcohol (-)-(3S)-4a. Plausible transition states are briefly discussed on the basis of PM3 conformational calculations. (C) 2001 Elsevier Science Ltd. All rights reserved.
Diastereoselective allylation of chiral imines and a stereocontrolled route to 4-hydroxy-N-tosylpipecolic acid derivatives
作者:Anna Kulesza、Adam Mieczkowski、Janusz Jurczak
DOI:10.1016/s0957-4166(02)00542-6
日期:2002.9
We report an asymmetric route to non-proteogenic amino acids, based on Lewis acid-mediated diastereoselective additions of allyltrimethylsilane to iminoglyoxylic acid derivatives bearing ester or amide chiral auxiliaries. Reactions of allyltrimethylsilane with N-tosyl- and N-phenyliminoglyoxylates of (R)-8-phenylmenthol proceeded with excellent diastereoselectivity (d.e. 98%). In contrast, the reactions of N-benzyliminoglyoxylates occurred with low diastereoselectivities and in poor yields. We have applied our methodology to develop a short synthesis of (2S,4R)-4-hydroxypipecolic acid derivatives. (C) 2002 Published by Elsevier Science Ltd.
Asymmetric addition of titanium and sodium alkoxides to chiral imines
A novel method for the alkoxylation of imines was developed using alkoxytitanium(IV) derivatives as the alkoxy nucleophile donors. A rationale of the results obtained using stereochemical models is proposed. The differences in the stereochemical outcome of the reaction with the titanium species and sodium alkoxides were studied as well as the influence of chiral auxiliaries such as (2R)-bornano-10,2-sultam, (R)-8-phenylmenthol and 10-N,N-dicyclohexylsulphamoyl-(R)-isoborneol. (C) 2003 Elsevier Science Ltd. All rights reserved.
The Diastereoselective Barbier-Type Addition to Chiral<i>N</i>-Tosylimines
作者:Janusz Jurczak、Anna Kulesza
DOI:10.1055/s-2003-41453
日期:——
The Barbier approach was used for diastereoselective formation of allylamino acid derivatives. The stereochemical models for nucleophilic addition to N-tosylimines bearing various chiral auxiliaries such as (2R)-bomano-10,2-sultam, (R)-8-phenylmenthol, and 10-N,N-dicyclohexylsulfamoyl-(R)-isobomeol are proposed.