Synthesis of Functionalized Azomethine Ylides via the Rh(II)-Catalyzed Cyclization of .alpha.-Diazo Carbonyls onto Imino .pi.-Bonds
摘要:
alpha-Diazo carbonyl compounds containing an imino group in the gamma-position have been found to undergo a rhodium(II) acetate induced cyclization reaction to generate cyclic azomethine ylides. The reactive dipole undergoes a subsequent 1,3-dipolar cycloaddition with added dipolarophiles. The imino/oxime nitrogen lone pair of electrons must be properly oriented so as to interact with the rhodium carbenoid. Thus, acyclic oxime ethers which exist in the proper E-configuration readily undergo the tandem cyclization-cycloaddition reaction. In sharp contrast, the isomeric Z-oximino diazo carbonyl system does not cyclize to an azomethine ylide but rather intramolecularly inserts into the oximino C-H bond. Addition of a catalytic amount of rhodium(II) acetate to (E)-2-(diazoacetyl)benzaldehyde O-methyloxime in the presence of DMAD or N-phenylmaleimide affords a dipolar cycloadduct in high yield. When p-quinone was used as the dipolarophile, the initially formed cycloadduct was treated with acetic anhydride to give a compound containing the basic core dibenzo[a,d]cyclohepten-5,10-imine skeleton found in MK-801. Cyclic imines such as isoxazolines were particularly effective substrates for azomethine ylide formation. The rhodium(II) catalyzed reaction of 3-(4-diazo-3-oxobutyl)-5-phenyl-Delta(2)-isoxazoline with DMAD produced a 4:1 mixture of diastereomeric cycloadducts in good yield. Cyclization of the rhodium carbenoid did not occur with the aromatic isoxazole system and this is presumably due to the low basicity of the nitrogen lone pair of electrons.
Synthesis of Functionalized Azomethine Ylides via the Rh(II)-Catalyzed Cyclization of .alpha.-Diazo Carbonyls onto Imino .pi.-Bonds
摘要:
alpha-Diazo carbonyl compounds containing an imino group in the gamma-position have been found to undergo a rhodium(II) acetate induced cyclization reaction to generate cyclic azomethine ylides. The reactive dipole undergoes a subsequent 1,3-dipolar cycloaddition with added dipolarophiles. The imino/oxime nitrogen lone pair of electrons must be properly oriented so as to interact with the rhodium carbenoid. Thus, acyclic oxime ethers which exist in the proper E-configuration readily undergo the tandem cyclization-cycloaddition reaction. In sharp contrast, the isomeric Z-oximino diazo carbonyl system does not cyclize to an azomethine ylide but rather intramolecularly inserts into the oximino C-H bond. Addition of a catalytic amount of rhodium(II) acetate to (E)-2-(diazoacetyl)benzaldehyde O-methyloxime in the presence of DMAD or N-phenylmaleimide affords a dipolar cycloadduct in high yield. When p-quinone was used as the dipolarophile, the initially formed cycloadduct was treated with acetic anhydride to give a compound containing the basic core dibenzo[a,d]cyclohepten-5,10-imine skeleton found in MK-801. Cyclic imines such as isoxazolines were particularly effective substrates for azomethine ylide formation. The rhodium(II) catalyzed reaction of 3-(4-diazo-3-oxobutyl)-5-phenyl-Delta(2)-isoxazoline with DMAD produced a 4:1 mixture of diastereomeric cycloadducts in good yield. Cyclization of the rhodium carbenoid did not occur with the aromatic isoxazole system and this is presumably due to the low basicity of the nitrogen lone pair of electrons.
Model Studies Directed toward the Total Synthesis of (±)-Ribasine. A Tandem Cyclization−Cycloaddition Route Leading to the Core Skeleton
作者:Albert Padwa、Laura Precedo、Mark A. Semones
DOI:10.1021/jo990136j
日期:1999.5.1
A series of alpha-diazo-beta-(o-carbomethoxy)-substituted aryl ketones were prepared and employed as model systems for a synthetic approach toward the alkaloid ribasine. Six-membered ring carbonyl ylide dipoles were generated by treating the diazoketones with a rhodium(II) catalyst. The initially formed dipole was trapped using a variety of dipolarophiles including N-benzylidene methylamine. The Rh(II)-catalyzed behavior of ethyl 2-diazo-3-(2-formylphenyl)-3-oxo-propionate was also studied to probe the chemoselectivity of the reaction. The major products isolated are derived from bimolecular trapping of the carbonyl ylide dipole, as well as intramolecular C-H insertion of the rhodium carbenoid into the aldehydic hydrogen. Changing the catalyst from Rh(II) trifluoroacetate to Rh(II) acetate caused a significant alteration in product distribution. A study of the tandem cyclization-cycloaddition reaction of an o-allyl phenyl substituted diazoketone was also carried out. An unexpected low-temperature intramolecular dipolar cycloaddition of the diazo group across the neighboring pi-bond first occurred, followed by nitrogen extrusion to give products derived from a 1,3-biradical intermediate. By subjecting the diazoketone to the Rh(II) catalyst at 110 degrees C, it was possible to prepare the carbonyl ylide derived cycloadduct in high yield. This result provides good precedent for the future implementation of the cycloaddition strategy toward the synthesis of ribasine.
Synthesis of Functionalized Azomethine Ylides via the Rh(II)-Catalyzed Cyclization of .alpha.-Diazo Carbonyls onto Imino .pi.-Bonds
作者:Albert Padwa、Dennis C. Dean、Martin H. Osterhout、Laura Precedo、Mark A. Semones
DOI:10.1021/jo00097a042
日期:1994.9
alpha-Diazo carbonyl compounds containing an imino group in the gamma-position have been found to undergo a rhodium(II) acetate induced cyclization reaction to generate cyclic azomethine ylides. The reactive dipole undergoes a subsequent 1,3-dipolar cycloaddition with added dipolarophiles. The imino/oxime nitrogen lone pair of electrons must be properly oriented so as to interact with the rhodium carbenoid. Thus, acyclic oxime ethers which exist in the proper E-configuration readily undergo the tandem cyclization-cycloaddition reaction. In sharp contrast, the isomeric Z-oximino diazo carbonyl system does not cyclize to an azomethine ylide but rather intramolecularly inserts into the oximino C-H bond. Addition of a catalytic amount of rhodium(II) acetate to (E)-2-(diazoacetyl)benzaldehyde O-methyloxime in the presence of DMAD or N-phenylmaleimide affords a dipolar cycloadduct in high yield. When p-quinone was used as the dipolarophile, the initially formed cycloadduct was treated with acetic anhydride to give a compound containing the basic core dibenzo[a,d]cyclohepten-5,10-imine skeleton found in MK-801. Cyclic imines such as isoxazolines were particularly effective substrates for azomethine ylide formation. The rhodium(II) catalyzed reaction of 3-(4-diazo-3-oxobutyl)-5-phenyl-Delta(2)-isoxazoline with DMAD produced a 4:1 mixture of diastereomeric cycloadducts in good yield. Cyclization of the rhodium carbenoid did not occur with the aromatic isoxazole system and this is presumably due to the low basicity of the nitrogen lone pair of electrons.