Development of an asymmetric approach to the 3,8-diazabicyclo[3.2.1]octane moiety of quinocarcin via intramolecular 1,3-dipolar cycloadditions of photochemically generated azomethine ylides
摘要:
Exploratory work culminating in an enantioselective approach to the DNA-reactive alkaloid quinocarcin (1) is detailed. The key step involves auxiliary-controlled dipolar cycloaddition between photochemically generated azomethine ylides such as 11 and Oppolzer's chiral acryloyl sultam (-)-32 to assemble the 6-exo-substituted 3,8-diazabicyclo[3.2.1]octane core of 1. The synthetic sequence begins with condensation of the benzylamines 3 and maleic anhydride to give the N-alkylated maleimides 6. Triazoline formation (MeN3) followed by photolytic (lambda > 3000 angstrom) extrusion of nitrogen leads to the corresponding aziridines 10. Upon irradiation at 2537 angstrom, these aziridines undergo electrocyclic ring-opening to give azomethine ylides 11, which can be trapped with (-)-32 to give the 6-exo-substituted cycloadduct 33 (diastereoselectivity, ds > 25:1). These results stand in sharp contrast to cycloadditions of 11 with (achiral and chiral) acrylate ester dipolarophiles as well as acrylonitrile, which proceed with no appreciable facial selectivity. The expected re-face selectivity of (-)-32 was confirmed in one case by X-ray crystallographic analysis of endo-adduct 35a. Removal (and recovery) of the chiral sultam auxiliary can be effected by titanium (IV)-mediated alcoholysis to give ester derivatives of the cycloadducts.
Development of an asymmetric approach to the 3,8-diazabicyclo[3.2.1]octane moiety of quinocarcin via intramolecular 1,3-dipolar cycloadditions of photochemically generated azomethine ylides
摘要:
Exploratory work culminating in an enantioselective approach to the DNA-reactive alkaloid quinocarcin (1) is detailed. The key step involves auxiliary-controlled dipolar cycloaddition between photochemically generated azomethine ylides such as 11 and Oppolzer's chiral acryloyl sultam (-)-32 to assemble the 6-exo-substituted 3,8-diazabicyclo[3.2.1]octane core of 1. The synthetic sequence begins with condensation of the benzylamines 3 and maleic anhydride to give the N-alkylated maleimides 6. Triazoline formation (MeN3) followed by photolytic (lambda > 3000 angstrom) extrusion of nitrogen leads to the corresponding aziridines 10. Upon irradiation at 2537 angstrom, these aziridines undergo electrocyclic ring-opening to give azomethine ylides 11, which can be trapped with (-)-32 to give the 6-exo-substituted cycloadduct 33 (diastereoselectivity, ds > 25:1). These results stand in sharp contrast to cycloadditions of 11 with (achiral and chiral) acrylate ester dipolarophiles as well as acrylonitrile, which proceed with no appreciable facial selectivity. The expected re-face selectivity of (-)-32 was confirmed in one case by X-ray crystallographic analysis of endo-adduct 35a. Removal (and recovery) of the chiral sultam auxiliary can be effected by titanium (IV)-mediated alcoholysis to give ester derivatives of the cycloadducts.
Microwave-induced One-pot Synthesis of N-carboxyalkyl Maleimides and Phthalimides†
作者:Harsha N. Borah、Romesh C. Boruah、Jagir S. Sandhu
DOI:10.1039/a707961c
日期:——
Maleic and phthalic anhydride condenses with amino acids and alkylamines under microwave irradiation to afford N-substituted maleimides and phthalimides in excellent yields.
Development of an asymmetric approach to the 3,8-diazabicyclo[3.2.1]octane moiety of quinocarcin via intramolecular 1,3-dipolar cycloadditions of photochemically generated azomethine ylides
作者:Philip Garner、Wen Bin Ho、Sunitha K. Grandhee、Wiley J. Youngs、Vance O. Kennedy
DOI:10.1021/jo00020a035
日期:1991.9
Exploratory work culminating in an enantioselective approach to the DNA-reactive alkaloid quinocarcin (1) is detailed. The key step involves auxiliary-controlled dipolar cycloaddition between photochemically generated azomethine ylides such as 11 and Oppolzer's chiral acryloyl sultam (-)-32 to assemble the 6-exo-substituted 3,8-diazabicyclo[3.2.1]octane core of 1. The synthetic sequence begins with condensation of the benzylamines 3 and maleic anhydride to give the N-alkylated maleimides 6. Triazoline formation (MeN3) followed by photolytic (lambda > 3000 angstrom) extrusion of nitrogen leads to the corresponding aziridines 10. Upon irradiation at 2537 angstrom, these aziridines undergo electrocyclic ring-opening to give azomethine ylides 11, which can be trapped with (-)-32 to give the 6-exo-substituted cycloadduct 33 (diastereoselectivity, ds > 25:1). These results stand in sharp contrast to cycloadditions of 11 with (achiral and chiral) acrylate ester dipolarophiles as well as acrylonitrile, which proceed with no appreciable facial selectivity. The expected re-face selectivity of (-)-32 was confirmed in one case by X-ray crystallographic analysis of endo-adduct 35a. Removal (and recovery) of the chiral sultam auxiliary can be effected by titanium (IV)-mediated alcoholysis to give ester derivatives of the cycloadducts.