Ether-directed diastereoselectivity in catalysed Overman rearrangement: comparative studies of metal catalysts
作者:Ieva Jaunzeme、Aigars Jirgensons
DOI:10.1016/j.tet.2008.03.099
日期:2008.6
Ether-directed diastereoselectivity in Overman rearrangement of delta-methoxy and delta-TBDMSO substituted allylic trichloroacetimidates has been explored using PtCl2, PtCl4, AuCl and AuCl3 catalysts in comparison with commonly used Pd(II) catalysts. For both substrates the use of PtCl2 catalyst gave notably improved anti/syn-ratio of 1,2-aminoalcohol derivatives (anti/syn=11:1 for 5-methoxy; 6:1 for delta-TBDMSO) compared to all metal catalysts known to promote Overman rearrangement. Formation of 2-trichloromethyloxazoline was observed as a dominant side reaction in the metal catalysed rearrangement of a-methoxy substituted allylic trichloroacetimidates considerably reducing the yield of the desired product. This side reaction was suppressed when delta-TBDMS-ether was used as a directing group. (C) 2008 Elsevier Ltd. All rights reserved.
Conformational Studies of Chiral .alpha.,.beta.-Unsaturated Aldehydes
作者:Benjamin W. Gung、Melinda S. Gerdeman、Rebecca A. Fouch、Mark A. Wolf
DOI:10.1021/jo00094a043
日期:1994.7
The conformational profiles for chiral alpha,beta-unsaturated aldehydes have been studied by a combination of ab initio MO methods and the variable-temperature MMR technique. The s-trans rotational isomer around the C-sp2-C-sp2 single bond is more stable than the s-cis conformer by similar to 500 cal/mol in chloroform. This difference is 950 cal/mol according to ab initio calculations at the MP2/6-31G* level of theory. The silyl ethers, 3a-d, prefer the C-O eclipsed form while the methyl ethers, 6a-d, favor the C-H eclipsed conformation for rotations around the C-sp3-C-sp2 bond.