8H-Anhydro-4-hydroxy-2-oxo-1,3-thiazinium Hydroxides as Mesoionic 1,4-Dipoles
摘要:
The previously unknown 8H-anhydro-4-hydroxy-2-oxo-1,3-thiazinium hydroxides (1) were prepared and their 1,4-dipolar cycloaddition behavior was examined. In most cases, elimination of the proton in the 8-position of the mesoionic ring was observed to occur unless extremely reactive dipolarophiles were used. The S,N-ketene acetals were converted to the corresponding alpha-diazo ketones for further study.
Intramolecular Cycloaddition of Isomunchnone Dipoles to Heteroaromatic .pi.-Systems
摘要:
A series of furanyl-, thienyl-, and indole-substituted diazo imides were prepared by treating the appropriate amides with diketene to give the N-acetoacylated imides. Exposure of the imides to standard diazo transfer conditions afforded the desired diazo imides. Treatment of these diazo imides bearing tethered heterocyclic rings with rhodium(II) acetate affords transient isomunchnone dipoles. The mesoionic dipoles are formed by cyclization of the rhodium carbenoid onto the neighboring amide carbonyl oxygen atom. The scope and limitations of the intramolecular 1,3-dipolar cycloaddition of the isomunchnones across a tethered furan and thiophene ring were studied. The facility of the internal cycloaddition is influenced by the length and nature of the tether connecting the dipole and dipolarophile functionalities. The reaction is critically dependent on conformational factors in the transition state. In addition, the first examples of intramolecular cycloaddition of isomunchnones to indole dipolarophiles are reported. Cycloadditions of this type generate highly functionalized polyheterocyclic systems with complete relative stereocontrol at the newly formed stereocenters.
Intramolecular Cycloaddition of Isomunchnone Dipoles to Heteroaromatic .pi.-Systems
作者:Albert Padwa、Donald L. Hertzog、William R. Nadler
DOI:10.1021/jo00102a037
日期:1994.11
A series of furanyl-, thienyl-, and indole-substituted diazo imides were prepared by treating the appropriate amides with diketene to give the N-acetoacylated imides. Exposure of the imides to standard diazo transfer conditions afforded the desired diazo imides. Treatment of these diazo imides bearing tethered heterocyclic rings with rhodium(II) acetate affords transient isomunchnone dipoles. The mesoionic dipoles are formed by cyclization of the rhodium carbenoid onto the neighboring amide carbonyl oxygen atom. The scope and limitations of the intramolecular 1,3-dipolar cycloaddition of the isomunchnones across a tethered furan and thiophene ring were studied. The facility of the internal cycloaddition is influenced by the length and nature of the tether connecting the dipole and dipolarophile functionalities. The reaction is critically dependent on conformational factors in the transition state. In addition, the first examples of intramolecular cycloaddition of isomunchnones to indole dipolarophiles are reported. Cycloadditions of this type generate highly functionalized polyheterocyclic systems with complete relative stereocontrol at the newly formed stereocenters.
8H-Anhydro-4-hydroxy-2-oxo-1,3-thiazinium Hydroxides as Mesoionic 1,4-Dipoles
作者:Albert Padwa、Steven J. Coats、Lazaros Hadjarapoglou
DOI:10.3987/com-93-s(b)16
日期:——
The previously unknown 8H-anhydro-4-hydroxy-2-oxo-1,3-thiazinium hydroxides (1) were prepared and their 1,4-dipolar cycloaddition behavior was examined. In most cases, elimination of the proton in the 8-position of the mesoionic ring was observed to occur unless extremely reactive dipolarophiles were used. The S,N-ketene acetals were converted to the corresponding alpha-diazo ketones for further study.