Complex induced proximity effects: .beta.-lithiations of carboxamides
摘要:
The R*,S* and the R*,R* diastereomers of N,N-diisopropyl-2,3-dideuterio-2-methyl-3-phenylpropanamide (5,6) have been used to investigate the diastereoselectivity of the beta-lithiation of N,N-diisopropyl-2-methyl-3-phenylpropanamide (4). The beta-lithiation of 4 is highly diastereoselective with the beta-proton that is in the same relative position as the beta-proton of diastereomer 6 being preferentially removed. The beta-lithio species derived from 4 is shown to be a pyramidal, organolithium reagent based on C-13 NMR. Lithiation of the R*,S* and the R*,R* diastereomers of N,N-diisopropyl-2-methyl-3-(phenylthio)butanamide (7, 8) and N,N-diisopropyl-2,3-dimethyl-4-pentenamide (9, 10) occur at the beta-position. Lithiation of the R*,S* and R*,R* diastereomers of N,N-diisopropyl-2-methyl-3-phenylbutanamide (11, 12) occurs at the beta-position for 11 and at the alpha-position for 12. A conformational model is shown to correlate with these observations. The beta-lithio species formed do not react diastereospecifically.
Synthesis of (E)-α,β-Unsaturated Amides with High Selectivity by Using Samarium Diiodide
摘要:
Stereoselective beta -elimination of 2-chloro-3-hydroxyamides 1 is achieved by using samarium diiodide to yield alpha,beta -unsaturated amides 2, in which the C=C bond is di- tri-, or tetrasubstituted. The starting compounds a are easily prepared by reaction of the corresponding lithium enolates of alpha -chloroamides with aldehydes or ketones at -78 degreesC. The influence of the reaction conditions and the structure of the starting compounds on the stereoselectivity of the beta -elimination reaction is also discussed.
Undirected Arene and Chelate-Assisted Olefin C-H Bond Activation: [Rh<sup>III</sup>Cp*]-Catalyzed Dehydrogenative Alkene-Arene Coupling as a New Pathway for the Selective Synthesis of Highly Substituted<i>Z</i>Olefins
作者:Joanna Wencel-Delord、Corinna Nimphius、Frederic W. Patureau、Frank Glorius
DOI:10.1002/asia.201101018
日期:2012.6
Undirected/Directed Cross‐Coupling: A new dehydrogenative RhIII‐catalyzed cross‐coupling reaction between bromoarenes bearing no directing group and vinylic substrates substituted by a chelating group is reported. An original reaction mechanism enables the use of internal alkenes in a Z‐selective coupling. The application of 1,3‐disubstituted or 1,2‐homodisubstituted arenes leads to the formation of highly functionalized
Stereospecific Cyclopropanation of Highly Substituted C−C Double Bonds Promoted by CrCl<sub>2</sub>. Stereoselective Synthesis of Cyclopropanecarboxamides and Cyclopropyl Ketones
作者:José M. Concellón、Humberto Rodríguez-Solla、Carmen Méjica、Elena G. Blanco
DOI:10.1021/ol070896d
日期:2007.8.1
(Z)-alpha,beta-enamides in which the C-C double bond is di-, tri-, or tetrasubstituted. In all cases the process is completely stereospecific and only a single diastereoisomer is obtained. In addition, cyclopropyl ketones were readily prepared by reaction of the cyclopropanecarboxamides (derived from morpholine) obtained with a range of organolithium compounds. A mechanism has been proposed to explain the cyclopropanation
CrCl<sub>2</sub>-Promoted Stereospecific and Stereoselective Alkyl- and Silylcyclopropanation of α,β-Unsaturated Amides
作者:José M. Concellón、Humberto Rodríguez-Solla、Carmen Méjica、Elena G. Blanco、Santiago García-Granda、M. Rosario Díaz
DOI:10.1021/jo800103t
日期:2008.5.1
An efficient chromium-promoted alkyl- or silylcyclopropanation of α,β-unsaturated amides is described. These reactions can be carried out on (E)- or (Z)-α,β-enamides in which the C−C double bond is di-, or trisubstituted. This process takes place with totalstereospecificity and the new stereogenic center is generated with high or total stereoselectivity. Some synthetic applications of the obtained
visible photosensitizers for energytransfer to alkenes. On this basis, the E→Z photoisomerization reactions of alkenes with various functional groups under blue light irradiation were performed with moderate to high selectivity. The mechanistic studies suggested that the reactions involved energytransfer (EnT) from the photo-excited copper acetylide to the alkene via the singlet excited state.