Neier, Reinhard

1999, Rubin, Yves, Ganapathi, Padma, Franz, Andreas, An, Yi-Zhong, Qian, Wenyuan, Neier, Reinhard

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.

1996, Franz, Andreas, Eschler, Pierre Yves, Tharin, Manuel, Stoeckli-Evans, Helen, Neier, Reinhard

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.

1999, Rubin, Yves, Ganapathi, Padma S., Franz, Andreas, An, Yi-Zhong, Qian, Wenyuan, Neier, Reinhard

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.

1996, Franz, Andreas, Eschler, Pierre-Yves, Tharin, Manuel, Stoeckli-Evans, Helen, Neier, Reinhard

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.

1998, Neuschütz, Klaus, Velker, Jörg, Neier, Reinhard

Diels-Alder reactions and sigmatropic rearrangements are of paramount importance in synthesis. The tandem Diels-Alder/sigmatropic rearrangement processes combining these two powerful methods is presented in this review. Both possible sequences of this tandem process are discussed and several successful examples of the synthesis of natural products using the combination of these two reactions as key step demonstrate the utility of these processes.