New Regiospecific Catalytic Approaches to 4,5-Dihydroisoxazoles and 2,5-Dihydroisoxazoles from O-Propargylic Hydroxylamines
作者:David Knight、Anthony Proctor、John Clough
DOI:10.1055/s-0029-1219365
日期:2010.3
Unprotected O-propargylic hydroxylamines undergo generally essentially quantitative cyclisations when exposed briefly to silver nitrate adsorbed onto silica gel to give 4,5-dihydroisoxazoles [2-isoxazolines], while N-protected derivatives give the corresponding 2,5-dihydroisoxazoles [3-isoxazolines] in similarly excellent yields, given that an appropriate functionality on nitrogen is used.
A facile method for the synthesis of O-alkylatedhydroximides through the acid-catalyzed alkylation of hydroximides by using benzylicalcohols as alkylating agents is described for the first time. The obtained O-propargylated products offered easy access to 2,5- and 4,5-dihydroisoxazoles.
Thermally-induced skeletal rearrangement of (Z)-O-propargylic α,β-unsaturated aldoximes to multisubstituted pyridine oxides
作者:Itaru Nakamura、Dong Zhang、Masahiro Terada
DOI:10.1016/j.tetlet.2011.09.107
日期:2011.11
(Z)-Propargylic oxime ethers derived from alpha,beta-unsaturated aldehydes were converted to the corresponding 2,3,6-trisubstituted pyridine oxides in moderate to acceptable yields with high regioselectivity. The reaction proceeds via a tandem thermal [2,3] rearrangement, 4 pi electrocyclization, and ring expansion. (C) 2011 Elsevier Ltd. All rights reserved.
Copper-Catalyzed Skeletal Rearrangement of O-Propargylic Aryloximes into Four-Membered Cyclic Nitrones - Chirality Transfer and Mechanistic Insight
Copper-catalyzed skeletal rearrangement of O-propargylic aryloximes (E)-1 were carried out to afford the corresponding four-membered cyclic nitrones 2 in good to excellent yields. The optimal reactions conditions of the highly regioselective reactions involved the use of [CuCl(cod)](2) in acetonitrile at 70 degrees C. In the case of (Z)-1, however, the reaction proceeded in the absence of the copper catalysts to afford the identical compound 2 in good yields. Furthermore, the reactions were also carried out using chiral substrates (R)-1 in the presence of Cu catalysts to afford (R)-2 with good levels of chirality transfer.