Triflic Anhydride Mediated Cyclization of 5-Hydroxy-Substituted Pyrrolidinones for the Preparation of α-Trifluoromethylsulfonamido Furans
作者:Albert Padwa、Paitoon Rashatasakhon、Mickea Rose
DOI:10.1021/jo0341970
日期:2003.6.1
(Tf(2)O) in pyridine resulted in the formation of various substituted sulfonamidofurans. The suggested mechanism involves initial formation of an iminium ion which is subsequently transformed into a transient imino triflate. Cyclization of the highly electrophilic imine onto the oxygen atom of the adjacent carbonyl group generates an imino dihydrofuran intermediate. This species reacts further with
Tandem Polar/Radical Crossover Sequences for the Formation of Fused and Bridged Bicyclic Nitrogen Heterocycles Involving Radical Ionic Chain Reactions, and Alkene Radical Cation Intermediates, Performed under Reducing Conditions: Scope and Limitations
anion contact ion pairs which are trappedintramolecularly in a tandem polar/radical crossover sequence involving radical ionic chain reactions by allylic and propargylic amines. The substitution pattern of the alkene radical cation dictates the cyclization mode, and this may be engineered to form fused ring systems by an initial exo-mode nucleophilic cyclization or bridged bicyclic systems when the nucleophilic
Zinc carbenoid-mediated chain extension of β-keto amides
作者:Ramona Hilgenkamp、Charles K Zercher
DOI:10.1016/s0040-4020(01)00879-1
日期:2001.10
The reaction of β-keto amides with ethyl(iodomethyl)zinc provides access to a wide variety of γ-keto amides, including primary, secondary, and tertiary amides. Although the reaction of α-substituted β-keto amides are in many cases unsatisfactory, the method can be applied to a broad spectrum of substrates that possess imide and olefinic functionality.
Generation and Trapping of Alkene Radical Cations under Nonoxidizing Conditions: Formation of Six-Membered Rings by <i>E</i><i>xo</i>- and <i>E</i><i>ndo</i>-Mode Cyclizations
作者:David Crich、Santhosh Neelamkavil
DOI:10.1021/ol026204x
日期:2002.7.1
[reaction: see text] It is demonstrated that alkene radicalcations generated by the radical ionic fragmentation of beta-(phosphatoxy)alkylradicals undergo efficient nucleophilic capture by amines in either the 6-exo or 6-endo modes, leading to six-membered nitrogen heterocycles. Suitable placement of an alkene enables the juxtaposition of a radical cyclization resulting in the formation of both the