Chemo- and stereoselectivity in the ring-openingreaction of epoxides with a reagent prepared from allylmagnesium halide and chlorotitanium triphenoxide is described. It has been proven that the allylating reagent can also be used for the reaction of epoxides bearing a tert-butyl ester, amide, or acetal moiety, and that the epoxide cleavage regioselectively takes place at the more substituted carbon
Photo-Organocatalytic Enantioselective Radical Cascade Reactions of Unactivated Olefins
作者:Pablo Bonilla、Yannick P. Rey、Catherine M. Holden、Paolo Melchiorre
DOI:10.1002/anie.201808183
日期:2018.9.24
Radical cascade processes are invaluable for their ability to rapidly construct complex chiral molecules from simple substrates. However, implementing catalytic asymmetric variants is difficult. Reported herein is a visible‐light‐mediated organocatalytic strategy that exploits the excited‐state reactivity of chiral iminium ions to trigger radical cascade reactions with high enantioselectivity. By combining
Intermolecular Heck Coupling with Hindered Alkenes Directed by Potassium Carboxylates
作者:Tucker R. Huffman、Yebin Wu、Alexis Emmerich、Ryan A. Shenvi
DOI:10.1002/anie.201813233
日期:2019.2.18
Pd0 -catalyzed Mizoroki-Heck reactions traditionally exhibit poor reactivity with polysubstituted, unbiased alkenes. Intermolecular reactions with simple, all-carbon tetrasubstituted alkenes are unprecedented. Herein we report that pendant carboxylic acids, combined with bulky monophospine ligands on palladium, can direct the arylation of tri- and tetrasubstituted olefins. Quaternary carbons are established
One-Pot Regio- and Stereoselective Cyclization of 1,2,<i>n</i>-Triols
作者:Tao Zheng、Radha S. Narayan、Jennifer M. Schomaker、Babak Borhan
DOI:10.1021/ja043002i
日期:2005.5.1
A simple and efficient process to cyclize triols containing a 1,2-diol functionality with a pendant hydroxyl group is presented. The one-pot procedure converts the 1,2-diol into an ortho ester in situ, which upon treatment with a Lewis acid generates a cyclic acetoxonium intermediate. This intermediate is subsequently trapped by the pendant hydroxyl group to generate a cyclic ether. The stereochemistry
3 undergo in the presence of trimethylsilyl chloride and catalytic amounts of FeCl 2 an intramolecular chloroamination (aminochlorination) reaction (Procedure 1). The corresponding oxazolidinones 2 and 4 are formed in moderate to excellent yields (47-99%). The same reagent combination can be employed to convert azides 6 of γ,δ-unsaturated carboxylic acids into the corresponding lactams 7. The latter