A Highly cis-Selective Synthesis of 2-Ethynylaziridines by Intramolecular Amination of Chiral Bromoallenes: Improvement of Stereoselectivity Based on the Computational Investigation
摘要:
The base-mediated intramolecular amination of bromoallenes having an axial chirality is described. The treatment of (4S,aR)-4-alkyl-4-[N-(arylsulfonyl)amino]-1-bromobuta-1,2-dienes with NaH in DMF affords 2,3-cis-2-ethynylaziridines in good to excellent selectivity (2,3-cis:trans = 92:8-99:1). The reaction of (4S,aS)-bromoallenes with NaH/DMF also gives 2,3-cis-2-ethynylaziridines selectively (79:21-91:9). These experimental results have been rationalized by 133LYP density functional calculations together with the 6-31 +G(d) basis set and the Onsager solvation model. The transition structures for cis-aziridine formation of both (4S,aR)- and (4S,aS)-bromoallenes in DMF are favored over the corresponding trans transition structures by 4.35 and 1.41 kcal/mol, respectively. Furthermore, the calculations predicted that a less polar solvent gives higher cis selectivity for (4S,aS)-bromoallenes. In fact, improvement of the cis selectivity to 99:1 has been realized by using a less polar solvent such as THF. The cyclization of bromoallenes bearing a beta- or gamma-amino group also affords four- and five-membered azacycles in a highly cis-selective manner.
Flash vacuum pyrolysis of stabilised phosphorus ylides. Part 17.1 Preparation of aliphatic amino acid derived γ-alkoxycarbonylamino-β-oxo ylides and pyrolysis to give α,β-acetylenic γ-amino acid and GABA analogues
Convenient synthesis of chiral α,β-acetylenic γ-amino acid derivatives and γ-aminobutyric acid analogues via stabilized ylides
作者:R. Alan Aitken、Nzaira Karodia
DOI:10.1039/cc9960002079
日期:——
Twelve examples of protected acetylenic amino acids are readily prepared in a two-step procedure involving formation and flash vacuum pyrolysis of chiral aminoacyl phosphorus ylides.
Flash vacuum pyrolysis of stabilised phosphorus ylides. Part 17.1 Preparation of aliphatic amino acid derived γ-alkoxycarbonylamino-β-oxo ylides and pyrolysis to give α,β-acetylenic γ-amino acid and GABA analogues
作者:R. Alan Aitken、Nazira Karodia、Tracy Massil、Robert J. Young
DOI:10.1039/b110243e
日期:2002.2.6
A series of eleven α-aminoacyl stabilised phosphorus ylides 9â19 have been prepared by condensation of N-alkoxycarbonyl protected amino acids with Ph3PCHCO2Et using a carbodiimide peptide coupling reagent. Upon flash vacuum pyrolysis at 600 °C, these undergo extrusion of Ph3PO to give the corresponding α,β-acetylenic γ-amino esters 21â29, 33 and 34 in moderate yield. In two cases the terminal alkynes 30 and 31 are also formed. The β-aminoacyl ylide 20 from β-alanine
similarly gives the α,β-acetylenic δ-amino ester 35 upon pyrolysis. Regioselective addition of HBr to the triple bond of one acetylenic ester 25 was observed giving a mixture of E and Z
α-bromoacrylates 36. Hydrogenation of the N-Cbz acetylenic esters 21â23 and 33 results in N-deprotection and hydrogenation of the triple bond to afford the chiral GABA analogues 37â40 in 70 â>95% ee as determined by 19F NMR of their Mosher amides. Fully assigned 13C NMR spectra of all the ylides and acetylenic ester derivatives are presented.
A Highly <i>cis</i>-Selective Synthesis of 2-Ethynylaziridines by Intramolecular Amination of Chiral Bromoallenes: Improvement of Stereoselectivity Based on the Computational Investigation
The base-mediated intramolecular amination of bromoallenes having an axial chirality is described. The treatment of (4S,aR)-4-alkyl-4-[N-(arylsulfonyl)amino]-1-bromobuta-1,2-dienes with NaH in DMF affords 2,3-cis-2-ethynylaziridines in good to excellent selectivity (2,3-cis:trans = 92:8-99:1). The reaction of (4S,aS)-bromoallenes with NaH/DMF also gives 2,3-cis-2-ethynylaziridines selectively (79:21-91:9). These experimental results have been rationalized by 133LYP density functional calculations together with the 6-31 +G(d) basis set and the Onsager solvation model. The transition structures for cis-aziridine formation of both (4S,aR)- and (4S,aS)-bromoallenes in DMF are favored over the corresponding trans transition structures by 4.35 and 1.41 kcal/mol, respectively. Furthermore, the calculations predicted that a less polar solvent gives higher cis selectivity for (4S,aS)-bromoallenes. In fact, improvement of the cis selectivity to 99:1 has been realized by using a less polar solvent such as THF. The cyclization of bromoallenes bearing a beta- or gamma-amino group also affords four- and five-membered azacycles in a highly cis-selective manner.