A Tandem Cyclization-Onium Ylide Rearrangement-Cycloaddition Sequence for the Synthesis of Benzo-Substituted Cyclopentenones
摘要:
A new annulation sequence leading to benzo-substituted cyclopentenones is effected by treating o-alkynyl-substituted alpha-diazoacetophenones containing tethered heteroatoms with Rh(II) carboxylates. The reaction involves addition of the initially formed keto carbenoid onto the acetylenic pi-bond to give a rearranged vinyl carbenoid. Sulfonium ylide formation occurred both intra- and intermolecularly when the reaction was carried out in the presence of a sulfide. In the case where an ether oxygen was present on the backbone of the vinyl carbenoid, the resulting oxonium ylide underwent a [1,2]- or [2,3]-shift to give the rearranged product. These cyclic metallocarbenoids were also found to interact with a neighboring carbonyl or oximino pi-bond to produce carbonyl or azomethine ylides. The 1,3-dipoles generated in this manner were trapped with dimethyl acetylenedicarboxylate. The domino transformation was also performed intramolecularly by attaching a trapping agent directly to the carbonyl group. Incorporation of an amido carbonyl on the alkyne side chain was found to dramatically alter the course of the tandem annulation reaction. A novel rearranged cycloadduct was formed in high yield whose structure was elucidated by X-ray crystallography. The mechanism for its formation involves the opening of a transient intermediate oxabicyclo[2.2.1]heptane followed by a Wagner-Meerwein rearrangement.
Rhodium carbenoid mediated cyclizations of o-alkynyl-substituted .alpha.-diazoacetophenones
摘要:
o-Alkynyl-substituted alpha-diazoacetophenones undergo facile cyclization to indenone derivatives upon treatment with catalytic quantities of Rh(II) carboxylates. A variety of structural influences were encountered by varying the nature of the substituent group attached to the alkyne carbon atom. The cyclization reaction involves addition of a rhodium stabilized carbenoid onto the acetylenic pi-bond to generate a vinyl carbenoid. The vinyl carbenoid was found to undergo both CH and CC migration as well as delta-CH insertion into the alkyl backbone. Different catalysts were shown to result in significant variation in the product ratios for these reactions. Treatment of o-(5-(allyloxy)-1-pentynyl)-alpha-diazoacetophenone with rhodium(II) mandelate afforded 2-(2-propen-1-yl)-2-(1-oxo-1H-indenyl)-2,3,4,5-tetrahydrofuran in high yield. The formation of this compound involves initial formation of a vinyl carbenoid which reacts with the neighboring oxygen atom to give an oxonium ylide which subsequently undergoes a 2,3-sigmatropic rearrangement. When 2-ethynyl-alpha-diazoacetophenone is used, only products derived from 6-endo closure are observed. Substituted o-alkynyl alpha-diazoacetophenones give products derived from 5-exo cyclization. The mode of ring closure is controlled by both steric and electronic factors.
Rhodium carbenoid mediated cyclizations of o-alkynyl-substituted .alpha.-diazoacetophenones
作者:Albert Padwa、Keith E. Krumpe、Jamal M. Kassir
DOI:10.1021/jo00044a032
日期:1992.8
o-Alkynyl-substituted alpha-diazoacetophenones undergo facile cyclization to indenone derivatives upon treatment with catalytic quantities of Rh(II) carboxylates. A variety of structural influences were encountered by varying the nature of the substituent group attached to the alkyne carbon atom. The cyclization reaction involves addition of a rhodium stabilized carbenoid onto the acetylenic pi-bond to generate a vinyl carbenoid. The vinyl carbenoid was found to undergo both CH and CC migration as well as delta-CH insertion into the alkyl backbone. Different catalysts were shown to result in significant variation in the product ratios for these reactions. Treatment of o-(5-(allyloxy)-1-pentynyl)-alpha-diazoacetophenone with rhodium(II) mandelate afforded 2-(2-propen-1-yl)-2-(1-oxo-1H-indenyl)-2,3,4,5-tetrahydrofuran in high yield. The formation of this compound involves initial formation of a vinyl carbenoid which reacts with the neighboring oxygen atom to give an oxonium ylide which subsequently undergoes a 2,3-sigmatropic rearrangement. When 2-ethynyl-alpha-diazoacetophenone is used, only products derived from 6-endo closure are observed. Substituted o-alkynyl alpha-diazoacetophenones give products derived from 5-exo cyclization. The mode of ring closure is controlled by both steric and electronic factors.
A Tandem Cyclization-Onium Ylide Rearrangement-Cycloaddition Sequence for the Synthesis of Benzo-Substituted Cyclopentenones
作者:Albert Padwa、Jamal M. Kassir、Mark A. Semones、M. David Weingarten
DOI:10.1021/jo00106a014
日期:1995.1
A new annulation sequence leading to benzo-substituted cyclopentenones is effected by treating o-alkynyl-substituted alpha-diazoacetophenones containing tethered heteroatoms with Rh(II) carboxylates. The reaction involves addition of the initially formed keto carbenoid onto the acetylenic pi-bond to give a rearranged vinyl carbenoid. Sulfonium ylide formation occurred both intra- and intermolecularly when the reaction was carried out in the presence of a sulfide. In the case where an ether oxygen was present on the backbone of the vinyl carbenoid, the resulting oxonium ylide underwent a [1,2]- or [2,3]-shift to give the rearranged product. These cyclic metallocarbenoids were also found to interact with a neighboring carbonyl or oximino pi-bond to produce carbonyl or azomethine ylides. The 1,3-dipoles generated in this manner were trapped with dimethyl acetylenedicarboxylate. The domino transformation was also performed intramolecularly by attaching a trapping agent directly to the carbonyl group. Incorporation of an amido carbonyl on the alkyne side chain was found to dramatically alter the course of the tandem annulation reaction. A novel rearranged cycloadduct was formed in high yield whose structure was elucidated by X-ray crystallography. The mechanism for its formation involves the opening of a transient intermediate oxabicyclo[2.2.1]heptane followed by a Wagner-Meerwein rearrangement.