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221.
Shigeki Sano Yoko Kuroda Katsuyuki Saito Yukiko Ose Yoshimitsu Nagao 《Tetrahedron》2006,62(51):11881-11890
(Z)-α-Fluoro-α,β-unsaturated esters (Z)-7a-f were stereoselectively prepared by a tandem reduction-olefination of triethyl 2-acyl-2-fluoro-2-phosphonoacetates 6a-f with NaBH4 in EtOH. A concise synthesis of Cbz-Gly-Ψ[(Z)-CFC]-Gly (26) as a dipeptide isostere was achieved via the tandem reduction-olefination of the corresponding 2-acyl-2-fluoro-2-phosphonoacetate 20. 相似文献
222.
The difficulty as well as the significance of the direct generation of metal enolates of alpha-CF(3) ketones cannot be easily understood by chemists unfamiliar with F. In sharp contrast to the sunny side of non-F, hydrocarbon chemistry, F chemistry has long been overshadowed. Metal enolates of carbonyl compounds are synthetically important in C-C bond-forming reactions. However, the metal enolates of fluorinated carbonyl compounds have been severely limited to alpha-F metal enolates. Alpha-CF(3) metal enolates have generally been recognized as unstable and difficult to prepare because of the facile beta-M-F elimination. However, we have developed a direct generation and synthetic application of alpha-CF(3) metal enolates. Therefore, the present results regarding the direct generation and synthetic use of metal enolates of alpha-CF(3) ketones might be recognized as a real breakthrough for the general use of metal enolates in F chemistry. 相似文献
223.
Ono M Takara Y Egami M Uranaka K Yoshimitsu H Matsushita S Fujiwara Y Ikeda T Nohara T 《Chemical & pharmaceutical bulletin》2006,54(2):237-239
Two new steroidal alkaloid glycosides, esculeosides C and D, have been isolated from the ripe fruit of Cherry tomato [Lycopersicon esculentum var. cerasiforme (DUNAL) ALEF.], along with three known steroidal alkaloid glycosides, esculeoside A, esculeoiside B, and lycoperoside G. Their chemical structures were determined on the basis of spectroscopic data. 相似文献
224.
Nagao Y Miyamoto S Miyamoto M Takeshige H Hayashi K Sano S Shiro M Yamaguchi K Sei Y 《Journal of the American Chemical Society》2006,128(30):9722-9729
New chiral sulfoxides (R(S),S)-3, (S(S),S)-3, (R(S),S)-4, and (S(S),S)-4 and known chiral sulfoxides (R(S))-5, (R(S))-6, and (R(S))-7 were synthesized, and the stereochemistry of the new sulfoxides (R(S),S)-3 and (R(S),S)-4 was determined by X-ray crystallographic analysis. In their crystallographic structures, the intramolecular nonbonded S...O close contacts were recognized. Analyses of several sulfoxide complexes including rac-11 with N,N-dimethylacetamide (DMAC) or N-methyl-2-pyrrolidone (NMP) in a MeOH solution utilizing cold-spray ionization mass spectrometry provided, for the first time, direct information for intermolecular nonbonded S...O interactions between sulfoxides and amide (or lactam) in a solution. Highly diastereoselective and enantioselective Pummerer reactions based on the concept of intermolecular and intramolecular nonbonded S...O interactions were performed by treatment of several chiral sulfoxides (R(S), S)-3, (S(S), S)-3, (R(S), S)-4, (S(S), S)-4, (R(S))-5, (R(S))-6, and (R(S))-7 with acetic anhydride and trimethylsilyl triflate (TMSOTf) in DMAC, NMP, N,N-dimethylformamide, and N-formylpiperidine. Mechanistic studies on these facile stereoselective Pummerer reactions revealed the necessity for the amide/TMSOTf complex, such as 26 or 27, to be an efficient activation reagent for Ac(2)O and a trapping reagent for the released acetate ion, and that DMAC and NMP had a positive effect on this highly stereoselective chiral transfer reaction. 相似文献