In ring-closing metathesis (RCM) reactions of enynes, the substituents on the multiplebonds are quite important. Although RCM of an enyne having a monosubstituted alkene proceeds smoothly using the first-generation ruthenium-carbene complex 1a, that of an enyne having a disubstituted alkene and internal alkyne using 1a does not proceed. However, the second-generation ruthenium-carbene complex 1b or
Developing a Diastereoselective Intramolecular [4 + 3] Cycloaddition of Nitrogen-Stabilized Oxyallyl Cations Derived from <i>N</i>-Sulfonyl-Substituted Allenamides
作者:Andrew G. Lohse、Richard P. Hsung、Mitchell D. Leider、Sunil K. Ghosh
DOI:10.1021/jo200147h
日期:2011.5.6
Efforts toward achieving a practical and diastereoselective intramolecular [4 + 3] cycloaddition of nitrogen-stabilizedoxyallylcations with tethered dienes are described. Epoxidation of N-sulfonyl substituted allenamides with dimethyldioxirane (DMDO) generates nitrogen-stabilizedoxyallylcations that readily undergo stereoselective [4 + 3] cycloaddition with dienes. Selectivity is found to depend
(Alkylthio)alkynes as Addends in the Co(0) Catalyzed Intramolecular Pauson-Khand Reaction. Substituent Driven Enhancements of Annulation Efficiency and Stereoselectivity
作者:Brian L. Pagenkopf、David B. Belanger、Donogh J. R. O'Mahony、Tom Livinghouse
DOI:10.1055/s-2000-6301
日期:——
Compared to terminal alkynes, (methylthio)alkynes are generally superior substrates for the thermally promoted, Co2(CO)8 catalyzed Pauson-Khand reaction of enynes and allenynes, providing enones in higher yields and with enhanced diastereoselectivity. Improvements in yield dependent upon the use of 2,2,2-trifluoroethanol as co-solvent and an apparent preference for endo selectivity with (ethoxy)alkynes are also disclosed.
A cationic Fe−NO complex catalyses the cycloisomerization of cyclopropyl enyne to fused non-canonical cyclobutanes with up to four consecutive stereocenters with exclusive diastereoselectivity. Only Ag(+I) was found to show comparable activity, albeit significantly lower reactivity.