Stereo and electronic effects in the rhodium(II)-mediated synthesis of polycyclic lactones and lactams from .alpha.-diazo ester and amide precursors
摘要:
The rhodium(II) carboxylate catalyzed decomposition of several alpha-diazo esters and amides has been studied. A series of 5-keto-1-diazo acetates were prepared by acylation of alpha-hydroxy ketones using the (p-toluenesulfonyl)hydrazone of glyoxylic acid chloride. Treatment of these compounds with Rh(II) acetate afforded products derived from carbenoid insertion into solvent. When the hydrogen atom of the diazo carbon was replaced with an electron-withdrawing substituent, smooth cyclization occurred to produce a carbonyl ylide dipole which was subsequently trapped with different dipolarophiles. A series of N-alkyl-2-diazo-3-oxobutylamides, when treated with a catalytic quantity of rhodium(II) acetate, gave furo[3,4-c]furans in good yield. The reaction proceeds via addition of a rhodium-stabilized carbenoid onto the acetylenic pi-bond to give a vinyl carbenoid which subsequently cyclizes onto the neighboring carbonyl group to produce the furan ring. N-Alkynyl-substituted 2-diazoacetamides were also found to cyclize onto the tethered alkyne unit. The resulting rhodium carbenoid can undergo intramolecular and bimolecular cyclopropanation depending on both electronic and conformational factors. Rotamer population of the starting diazoamide was also found to influence product distribution.
Stereo and electronic effects in the rhodium(II)-mediated synthesis of polycyclic lactones and lactams from .alpha.-diazo ester and amide precursors
摘要:
The rhodium(II) carboxylate catalyzed decomposition of several alpha-diazo esters and amides has been studied. A series of 5-keto-1-diazo acetates were prepared by acylation of alpha-hydroxy ketones using the (p-toluenesulfonyl)hydrazone of glyoxylic acid chloride. Treatment of these compounds with Rh(II) acetate afforded products derived from carbenoid insertion into solvent. When the hydrogen atom of the diazo carbon was replaced with an electron-withdrawing substituent, smooth cyclization occurred to produce a carbonyl ylide dipole which was subsequently trapped with different dipolarophiles. A series of N-alkyl-2-diazo-3-oxobutylamides, when treated with a catalytic quantity of rhodium(II) acetate, gave furo[3,4-c]furans in good yield. The reaction proceeds via addition of a rhodium-stabilized carbenoid onto the acetylenic pi-bond to give a vinyl carbenoid which subsequently cyclizes onto the neighboring carbonyl group to produce the furan ring. N-Alkynyl-substituted 2-diazoacetamides were also found to cyclize onto the tethered alkyne unit. The resulting rhodium carbenoid can undergo intramolecular and bimolecular cyclopropanation depending on both electronic and conformational factors. Rotamer population of the starting diazoamide was also found to influence product distribution.
Tandem cyclization-cycloaddition reaction of rhodium carbenoids. Studies dealing with intramolecular cycloadditions
作者:Albert Padwa、Susan F. Hornbuckle、Glen E. Fryxell、Zhijia J. Zhang
DOI:10.1021/jo00047a032
日期:1992.10
A series of 5-alkenyl-1-diazo-2,5-pentanediones, when treated with a catalytic quantity of rhodium(II) acetate, were found to give cycloadducts derived from the intramolecular trapping of a carbonyl ylide intermediate. Tethers of three or four methylenes readily enter into intramolecular cycloaddition, while longer and shorter tethers were reluctant to do so. Alkenes attached to the formally cationic terminus of the carbonyl ylide readily undergo internal cycloaddition if the tether allows for a relatively strain-free transition state. The internal cycloaddition reaction does not occur when the olefinic side chain is attached by means of an ester functionality. Bimolecular trapping experiments established that carbonyl ylide formation occurred, but the dipole does not undergo intramolecular cycloaddition. The inability of these alpha-diazo keto esters to undergo internal cycloaddition is related to conformational factors. The equilibrium between the two possible conformations of the dipole lies predominantly on the side of the Z-isomer. In this orientation, intramolecular dipolar cycloaddition cannot occur, and instead the dipole collapses by means of a proton transfer to give an enol ether.
Stereo and electronic effects in the rhodium(II)-mediated synthesis of polycyclic lactones and lactams from .alpha.-diazo ester and amide precursors
作者:Albert Padwa、Dennis C. Dean、David J. Fairfax、Simon L. Xu
DOI:10.1021/jo00069a030
日期:1993.8
The rhodium(II) carboxylate catalyzed decomposition of several alpha-diazo esters and amides has been studied. A series of 5-keto-1-diazo acetates were prepared by acylation of alpha-hydroxy ketones using the (p-toluenesulfonyl)hydrazone of glyoxylic acid chloride. Treatment of these compounds with Rh(II) acetate afforded products derived from carbenoid insertion into solvent. When the hydrogen atom of the diazo carbon was replaced with an electron-withdrawing substituent, smooth cyclization occurred to produce a carbonyl ylide dipole which was subsequently trapped with different dipolarophiles. A series of N-alkyl-2-diazo-3-oxobutylamides, when treated with a catalytic quantity of rhodium(II) acetate, gave furo[3,4-c]furans in good yield. The reaction proceeds via addition of a rhodium-stabilized carbenoid onto the acetylenic pi-bond to give a vinyl carbenoid which subsequently cyclizes onto the neighboring carbonyl group to produce the furan ring. N-Alkynyl-substituted 2-diazoacetamides were also found to cyclize onto the tethered alkyne unit. The resulting rhodium carbenoid can undergo intramolecular and bimolecular cyclopropanation depending on both electronic and conformational factors. Rotamer population of the starting diazoamide was also found to influence product distribution.