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Tandem nucleophilic addition/Diels-Alder reaction of N-butadienyl N,O-ketene silyl acetals with C-60: Stereoselective formation of bicyclic octahydroquinoline-1,2,3,4-tetrahydrobuckminsterfullerenes and combined NMR spectroscopic and computational evaluation of the functionalization reactions
We have studied the reactivity of the N,O-ketene N-1,3-butadienyl-N-alkyl-O-silyl acetals 1a-e with C-60 proceeding through a tandem process to give the adducts 2a-e, The addition order of these tandem reactions has been evaluated. The initial nucleophilic Michael-like addition of the electron-rich N,O-ketene acetal moiety proceeds unusually fast at 25 degrees C, followed by an intramolecularly accelerated Diels-Alder step that is highly diastereoselective. The structures of compounds 2a-e were determined from the H-1 and C-13 NMR shifts and from II-II coupling patterns, while their stereochemistry was deduced from 2D T-ROESY NMR experiments. The proposed mechanism for the nucleophilic addition involves single electron transfer followed by radical anion-radical cation recombination. Computational investigations of the reaction pathways, transition states, and conformational energies have been carried out to corroborate the experimental data.
Preparation of N-alkylketene-N-butadienyl-N,O-silyl acetals
The synthesis of a series of dienamides 5a-j using Oppolzer's method is described. Using Rathke's method the ketene N,O-silyl acetals 6a-j can be obtained in good yield from the corresponding dienamides. The ketene acetals are obtained free of base and free of salts. They are stable and can be stored at - 20 degrees C. The new dienes are useful reagents for tandem reactions.
An Unexpected Tandem Reaction of N-Butadienyl-N-Alkylketene-N, O-Silylacetals
An Unexpected Tandem Reaction between N-Butadienyl-N-Alkylketene N,O-Trimethylsilylacetals of Propionamide and Activated Dienophiles like N-Phenylmaleimide or Acryloyl Chloride
Starting from the N-butadienyl-N-alkylpropionamides 1a-1c the corresponding N,O-trimethylsilylacetals could be obtained using the mixture of LDA and trimethylsilyl chloride in THF. The unexpected reaction sequence Diels-Alder reaction/acylation between the N-butadienyl-N-alkylketene N,O-trimethylsilylacetal of propionamide (2a-2b) and N-phenylmaleimide produced tricyclic products rac-5a -rac-5b and bicyclic products rac-6a - rac-6b with high diastereoselectivity. The reaction of the N,O-trimethylsilylacetals 2a and 2c with acryloyl chloride in a similar sequence gave the bicyclic products rac-8a and rac-8c. The stepwise synthesis of bicyclic systems of this general structure could only be successfully executed in 26% yield treating the Diels-Alder product rac-10 with LDA.
Tandem Nucleophilic Addition/Diels-Alder Reaction of N-Butadienyl N,O-Ketene Silyl Acetals with C60: Stereoselective Formation of Bicyclic Octahydroquinolino-1,2,3,4-Tetrahydrobuckminsterfullerenes and Combined NMR Spectroscopic and Computational Evaluation of the Functionalization Reactions
Abstract: We have studied the reactivity of the N,0-ketene N-l,3-butadienyl-N-alkyl-0-silyl acetals 1a-e with C60 proceeding through a tandem process to give the adducts 2a-e. The addition order of these tandem reactions has been evaluated. The initial nucleophilic Michael-like addition of the electron-rich N,O-ketene acetal moiety proceeds unusually fast at 25°C, followed by an intramolecularly accelerated Diels-Alder step that is highly diastereoselective. The structures of compounds 2a-e were determined from the 1H and 13C NMR shifts and from H - H coupling patterns, while their stereochemistry was deduced from 2D T-ROESY NMR experiments. The proposed mechanism for the nucleophilic addition involves single electron transfer followed by radical anion - radical cation recombination. Computational investigations of the reaction pathways, transition states, and conformational energies have been carried out to corroborate the experimental data.
The preparation and the cascade reactions of N-butadienyl-N-alkylketene N,O-tert-butyldimethylsilyl acetals
The preparation of N-butadienyl-N-alkylketene N,O-tert-butyldimethylsilyl acetals (11a-d) from readily available starting materials is described. The cascade Diels-Alder reaction followed by acylation of these ketene acetals yields bicyclic and tricyclic products 7, 13a,b and 14c,d with high diastereoselectivity. Copyright (C) 1996 Elsevier Science Ltd
The preparation and the cascade reactions of N-butadienyl-N-alkylketeneN,O-tert-butyldimethylsilyl acetals
The preparation of N-butadienyl-N-alkylketene N,O-tert-butyldimethylsilyl acetals (11a - d) from readily available starting materials is described. The cascade Diels-Alder reaction followed by acylation of these ketene acetals yields bicyclic and tricyclic products 7.13a,b and 14c,d with high diastereoselectivity.
Tandem cycloadditions of N,O-ketene N-1,3-butadienyl-N-alkyo-O-silylacetals with C-60: A straightforward stereoselective synthesis of bicyclic derivatives of 1,2,3,4-tetrahydrobuckminsterfullerene
We have studied the reactivity of the N,O-ketene N-1,3-butadienyl-N-alkyl-O-silylacetals 1a-e with C-60 which proceeds through a tandem process to give the adducts 2a-e with high diastereoselectivity. The addition order of these tandem reactions has been evaluated, The structures of compounds 2a-e were determined from the H-1 and C-13 NMR shifts and from the H-H coupling patterns, while the stereochemistry was deduced from 2D T-ROESY NMR experiments. The proposed mechanism for the Michael-type addition step is a single electron transfer, and the source of the C-60-attached proton is discussed.
Tandem reactions combining Diels-Alder reactions with sigmatropic rearrangements
The developpement of tandem reactions combining Diels-Alder reactions with sigmatropic rearrangements and their application in synthesis will be discussed. [Equation Omitted]. [on SciFinder(R)]
Preparation of N-Alkylketene-N-Butadienyl-N,O-Silyl Acetals
The synthesis of a series of dienamides 5a-j using Oppolzer’s method is described. Using Rathke’s method the ketene N,O-silyl acetals 6a-j can be obtained in good yield from the corresponding dienamines. The ketene acetals are obtained free of base and free of salts. They are stable and can be stored at -20°C. The new dienes are useful reagents for tandem reactions.