New chiral auxiliaries based on conformation control, a C2-symmetric 2,2-dimethylimidazolidine and 4-chiral, 2,2-dialkyloxazolidines. Synthesis and conformational analysis of acrylamide derivatives
作者:Shuji Kanemasa、Kenjiro Onimura
DOI:10.1016/s0040-4020(01)89439-4
日期:——
New chirality-controlling auxiliaries, a C2-symmetric 2,2-dimethylimidazolidine and 4-chiral 2,2-dialkyloxazolidines, are readily prepared from a C2-SYMMetriC 1,2-ethanediamine and naturally occurring alpha-amino acids, respectively. Conformational analysis of their N-acryloyl derivatives has been carried out on the basis of dynamic H-1 NMR spectroscopy and molecular mechanics calculations using MM2 program. Proper choice of the substituents at 2-, 4-, and 5-positions, in the oxazolidine cases, leads to the most effective chiral shielding of a diastereotopic acryloyl face.
3-Hydroxypyrroles and 1H-pyrrol-3(2H)-ones. Part 14.1,2 Pyrolysis of oxazolidinylmethylene derivatives of Meldrum's acid – synthesis of N-alkenyl-3-hydroxypyrroles and related reactions
作者:Abd El-Aal M. Gaber、Gordon A. Hunter、Hamish McNab
DOI:10.1039/b109788a
日期:2002.2.6
Flash vacuum pyrolysis (FVP) of the title compounds 14 and 17 at 600–625 °C (0.005 Torr) gives the N-alkenylpyrrolones 22 and 23 respectively. The mechanism is shown to involve hydrogen transfer and cyclisation of the methyleneketene intermediate (e.g.25) to a fused pyrrolone (e.g.28). This species fragments to create an azomethine ylide which provides the alkenyl substituent by a further hydrogen