Electrophilic cyclization of N-alkenylamides using a chloramine-T/I2 system
摘要:
A new protocol for the cyclization of N-alkenylamides using chloramine-T and iodine is described. When N-alkenylsulfonamides are treated with chloramine-T and iodine, three- to six-membered N-heterocycles are obtained with complete stereoselectivity. The method is compatible with the cyclization of the allylbenzamide or allylbenzthioamide to afford an oxazoline or thiazoline derivative, respectively. Mechanistic studies indicate that the chloramine-T/I-2 system functions as an effective iodonium species. (c) 2006 Elsevier Ltd. All rights reserved.
作者:Tietze, Lutz F.、Bratz, Matthias、Pretor, Martina
DOI:——
日期:——
Correlation between Functionality Preference of Ru Carbenes and <i>exo</i>/<i>endo</i> Product Selectivity for Clarifying the Mechanism of Ring-Closing Enyne Metathesis
Functionality preferences of metathesis Ru carbenes to various alkenes and alkynes with electronic and steric diversity were determined by using time-dependent fluorescence quenching. The functionality preferences depend not only on the properties of multiple bonds but also on the ligands on Ru. There was a good correlation between functionality preference and the metathesis reaction outcome. The correlation between functionality preference and exo/endo product ratio offers a solution to resolve the mechanistic issue related with alkene- vs alkyne-initiated pathway in ring-closing enyne metathesis. The correlation indicates the preference is likely to dictate the reaction pathway and eventually the outcome of the reaction. The Ru catalyst favoring alkyne over alkene provides more endo product, indicating that the reaction mainly initiates at the alkyne. By changing the substitution pattern, the preference can be reversed to give an exclusive exo product.
Mild Conditions for Pd-Catalyzed Carboamination of <i>N</i>-Protected Hex-4-enylamines and 1-, 3-, and 4-Substituted Pent-4-enylamines. Scope, Limitations, and Mechanism of Pyrrolidine Formation
作者:Myra Beaudoin Bertrand、Joshua D. Neukom、John P. Wolfe
DOI:10.1021/jo801631v
日期:2008.11.21
with aryl bromides leads to greatly increased tolerance of functional groups and alkene substitution. Substrates derived from (E)- or (Z)-hex-4-enylamines are stereospecifically converted to 2,1'-disubstituted pyrrolidine products that result from suprafacial addition of the nitrogen atom and the aryl group across the alkene. Transformations of 4-substituted pent-4-enylamine derivatives proceed in high
A new protocol for the cyclization of N-alkenylamides using chloramine-T and iodine is described. When N-alkenylsulfonamides are treated with chloramine-T and iodine, three- to six-membered N-heterocycles are obtained with complete stereoselectivity. The method is compatible with the cyclization of the allylbenzamide or allylbenzthioamide to afford an oxazoline or thiazoline derivative, respectively. Mechanistic studies indicate that the chloramine-T/I-2 system functions as an effective iodonium species. (c) 2006 Elsevier Ltd. All rights reserved.