Non-destructive Cleavage ofN-Acylsultams Under Neutral Conditions: Preparation of Enantiomerically, Pure Fmoc-Protected ?-Amino Acids
作者:Wolfgang Oppolzer、Phillippe Lienard
DOI:10.1002/hlca.19920750812
日期:1992.12.16
Heating diastereoisomerically pure N-acylsultams 3 or 4 with allyl alcohol/Ti(OR)4 efficiently yields sultams 1 or 2 and allyl esters 5. Esters 5 are hydrolyzed under nonbasic conditions in the presence of Wilkinson's catalyst to give enantiomerically and diastereoisomerically pure carboxylic acids 7. A series of [(fluoren-9-yl)methoxy]-carbonyl-(Fmoc)-protected amino acids 14 were thus prepared from
用烯丙醇/ Ti(OR)4加热非对映异构纯N-酰基磺酰胺3或4,可有效产生阿磺胺1或2和烯丙基酯5。在威尔金森氏催化剂的存在下,在非碱性条件下将酯5水解,得到对映异构和非对映异构纯的羧酸7。因此,由N- [ N '-(Fmoc)氨基]酰基苏丹酰胺12制备了一系列[[芴-9-基)甲氧基]-羰基-(Fmoc)-保护的氨基酸14。
Stereoselective aldol condensations via boron enolates
作者:D. A. Evans、J. V. Nelson、E. Vogel、T. R. Taber
DOI:10.1021/ja00401a031
日期:1981.6
carboxylic acid derivatives with dialkylboryl triflates in the presence of a tertiary amine and the subsequent aldol condensations of these boron enolates was conducted. The stereochemistry of the enolates formed from acyclic ketones was found to be dependent on the structure of the ketone, the dialkylboryl triflate, and the tertiary amine. A mechanism for the enolization involving initial coordination of
Asymmetric aldol reaction of amide enolates bearing -2,5-disubstituted pyrrolidines as chiral auxiliaries
作者:Tsutomu Katsuki、Masaru Yamaguchi
DOI:10.1016/s0040-4039(00)98932-9
日期:——
Condensation of aldehydes with Zr enolate of chiral -propionyl--2,5-disubstituted pyrrolidine proceeded with high diastereo- and diastereoface-selection. Stereoselectivity in the reaction of the corresponding -acetyl compounds was also examined.
Enantioselective aldol condensations. 3. Erythro-selective condensations via zirconium enolates
作者:D. A. Evans、L. R. McGee
DOI:10.1021/ja00400a071
日期:1981.5
a twisted allene structure 8.'O The loss of activity with increase in temperature further suggests that 8 may rapidly racemize through an intermediate or transition state that can be represented by any of the three structures 6, 11, or 12 or a diradical. Finally, since concerted opening of optically active 8 to 9 should give an active hydrocarbon, 13 was allowed to react with potassium menthoxide in
Aldol reactions of α-(N,N-dibenzylamino) ethyl ketones
作者:Jane Betty Goh、Bharat R. Lagu、Julie Wurster、Dennis C. Liotta
DOI:10.1016/0040-4039(94)88066-2
日期:1994.8
Aldol reactions of the sodium enolates of α-(N,N-dibenzylamino) ethyl ketones proceed in a highly diastereoselective fashion and result in the formation of the all syn adduct. The observed stereoselectivities are most easily understood in the context of an open transition state.