Chiral linker. Part 3: Synthesis and evaluation of aryl substituted m-hydrobenzoins as solid supported open chain chiral auxiliaries for the diastereoselective reduction of α-keto esters
摘要:
Five partly novel aryl substituted m-hydrobenzoins were synthesized and the corresponding desymmetrized hydrobenzoin ethers evaluated as open chain chiral auxiliaries in the L-Selectride (R) mediated stereoselective reduction of phenylglyoxylates, resulting in de values of up to 91%. Two optimized auxiliary structures were immobilized on commercially available Wang-resin and applied as a reusable solid supported chiral auxiliary in the same type of reaction. (c) 2006 Elsevier Ltd. All rights reserved.
Preparation, characterization and use of 1,3-disulfonic acid imidazolium hydrogen sulfate as an efficient, halogen-free and reusable ionic liquid catalyst for the trimethylsilyl protection of hydroxyl groups and deprotection of the obtained trimethylsilanes
摘要:
Novel 1,3-disulfonic acid imidazolium hydrogen sulfate, a halogen-free ionic liquid, is a recyclable and eco-benign catalyst for the trimethylsilyl protection of hydroxyl groups at room temperature under solvent free conditions to afford trimethylsilanes in excellent yields (92-100%) and in very short reaction times (1-5 min). Deprotection of the resulting trimethylsilanes can also be achieved using the same catalyst in methanol. The catalyst was characterized by IR. H-1 NMR, C-13 NMR and MS studies. All the products were extensively characterized by IR, H-1 NMR, MS, and elemental and melting point analyses. This new method consistently has the advantages of excellent yields and short reaction times. Further, the catalyst can be recovered and reused for several times without loss of activity. The work-up of the reaction consists of a simple separation, followed by concentration of the crude product and purification. (C) 2012 Elsevier B.V. All rights reserved.
Preparation, characterization and use of 1,3-disulfonic acid imidazolium hydrogen sulfate as an efficient, halogen-free and reusable ionic liquid catalyst for the trimethylsilyl protection of hydroxyl groups and deprotection of the obtained trimethylsilanes
Novel 1,3-disulfonic acid imidazolium hydrogen sulfate, a halogen-free ionic liquid, is a recyclable and eco-benign catalyst for the trimethylsilyl protection of hydroxyl groups at room temperature under solvent free conditions to afford trimethylsilanes in excellent yields (92-100%) and in very short reaction times (1-5 min). Deprotection of the resulting trimethylsilanes can also be achieved using the same catalyst in methanol. The catalyst was characterized by IR. H-1 NMR, C-13 NMR and MS studies. All the products were extensively characterized by IR, H-1 NMR, MS, and elemental and melting point analyses. This new method consistently has the advantages of excellent yields and short reaction times. Further, the catalyst can be recovered and reused for several times without loss of activity. The work-up of the reaction consists of a simple separation, followed by concentration of the crude product and purification. (C) 2012 Elsevier B.V. All rights reserved.
Chiral linker. Part 3: Synthesis and evaluation of aryl substituted m-hydrobenzoins as solid supported open chain chiral auxiliaries for the diastereoselective reduction of α-keto esters
Five partly novel aryl substituted m-hydrobenzoins were synthesized and the corresponding desymmetrized hydrobenzoin ethers evaluated as open chain chiral auxiliaries in the L-Selectride (R) mediated stereoselective reduction of phenylglyoxylates, resulting in de values of up to 91%. Two optimized auxiliary structures were immobilized on commercially available Wang-resin and applied as a reusable solid supported chiral auxiliary in the same type of reaction. (c) 2006 Elsevier Ltd. All rights reserved.